[KEYCLOAK-16341] Make the new stream-based methods in server-spi user interfaces default instead of the collection-based versions.

- this ensures that providing implementation for the collection-based methods is enough, which preserves
   backwards compatibility with older custom implementations.
 - alternative interfaces now allow new implementations to focus on the stream variants of the query methods.

federation/ldap/src/main/java/org/keycloak/storage/ldap/LDAPStorageProvider.java

@@ -92,7 +92,7 @@ public class LDAPStorageProvider implements UserStorageProvider,
         CredentialAuthentication,
         UserLookupProvider,
         UserRegistrationProvider,
-        UserQueryProvider,
+        UserQueryProvider.Streams,
         ImportedUserValidation {
     private static final Logger logger = Logger.getLogger(LDAPStorageProvider.class);
 

federation/ldap/src/main/java/org/keycloak/storage/ldap/ReadonlyLDAPUserModelDelegate.java

@@ -32,7 +32,7 @@ import org.keycloak.storage.ReadOnlyException;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class ReadonlyLDAPUserModelDelegate extends UserModelDelegate implements UserModel {
+public class ReadonlyLDAPUserModelDelegate extends UserModelDelegate {
 
     public ReadonlyLDAPUserModelDelegate(UserModel delegate) {
         super(delegate);

model/infinispan/src/main/java/org/keycloak/models/cache/infinispan/GroupAdapter.java

@@ -36,7 +36,7 @@ import java.util.stream.Stream;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class GroupAdapter implements GroupModel {
+public class GroupAdapter implements GroupModel.Streams {
 
     protected final CachedGroup cached;
     protected final RealmCacheSession cacheSession;

model/infinispan/src/main/java/org/keycloak/models/cache/infinispan/UserAdapter.java

@@ -42,7 +42,7 @@ import java.util.stream.Stream;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class UserAdapter implements CachedUserModel {
+public class UserAdapter implements CachedUserModel.Streams {
 
     private final Supplier<UserModel> modelSupplier;
     protected final CachedUser cached;

model/infinispan/src/main/java/org/keycloak/models/cache/infinispan/UserCacheSession.java

@@ -71,7 +71,7 @@ import java.util.stream.Stream;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class UserCacheSession implements UserCache {
+public class UserCacheSession implements UserCache.Streams {
     protected static final Logger logger = Logger.getLogger(UserCacheSession.class);
     protected UserCacheManager cache;
     protected KeycloakSession session;

model/jpa/src/main/java/org/keycloak/models/jpa/GroupAdapter.java

@@ -31,12 +31,10 @@ import org.keycloak.models.utils.RoleUtils;
 import javax.persistence.EntityManager;
 import javax.persistence.TypedQuery;
 import java.util.ArrayList;
-import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
 import java.util.stream.Stream;
 import javax.persistence.LockModeType;
 
@@ -46,7 +44,7 @@ import static org.keycloak.utils.StreamsUtil.closing;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class GroupAdapter implements GroupModel , JpaModel<GroupEntity> {
+public class GroupAdapter implements GroupModel.Streams , JpaModel<GroupEntity> {
 
     protected GroupEntity group;
     protected EntityManager em;

model/jpa/src/main/java/org/keycloak/models/jpa/JpaUserProvider.java

@@ -82,7 +82,7 @@ import static org.keycloak.utils.StreamsUtil.closing;
  * @version $Revision: 1 $
  */
 @SuppressWarnings("JpaQueryApiInspection")
-public class JpaUserProvider implements UserProvider, UserCredentialStore {
+public class JpaUserProvider implements UserProvider.Streams, UserCredentialStore {
 
     private static final String EMAIL = "email";
     private static final String EMAIL_VERIFIED = "emailVerified";

model/jpa/src/main/java/org/keycloak/models/jpa/UserAdapter.java

@@ -53,7 +53,7 @@ import static org.keycloak.utils.StreamsUtil.closing;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class UserAdapter implements UserModel, JpaModel<UserEntity> {
+public class UserAdapter implements UserModel.Streams, JpaModel<UserEntity> {
 
     protected UserEntity user;
     protected EntityManager em;

model/jpa/src/main/java/org/keycloak/storage/jpa/JpaUserFederatedStorageProvider.java

@@ -70,7 +70,7 @@ import static org.keycloak.utils.StreamsUtil.closing;
  * @version $Revision: 1 $
  */
 public class JpaUserFederatedStorageProvider implements
-        UserFederatedStorageProvider,
+        UserFederatedStorageProvider.Streams,
         UserCredentialStore {
 
     protected static final Logger logger = Logger.getLogger(JpaUserFederatedStorageProvider.class);

model/map/src/main/java/org/keycloak/models/map/group/AbstractGroupModel.java

@@ -24,7 +24,7 @@ import org.keycloak.models.map.common.AbstractEntity;
 
 import java.util.Objects;
 
-public abstract class AbstractGroupModel<E extends AbstractEntity> implements GroupModel {
+public abstract class AbstractGroupModel<E extends AbstractEntity> implements GroupModel.Streams {
 
     protected final KeycloakSession session;
     protected final RealmModel realm;

server-spi-private/src/main/java/org/keycloak/storage/adapter/InMemoryUserAdapter.java

@@ -31,7 +31,6 @@ import org.keycloak.models.utils.RoleUtils;
 import org.keycloak.storage.ReadOnlyException;
 
 import java.util.HashSet;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -41,7 +40,7 @@ import java.util.stream.Stream;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class InMemoryUserAdapter extends UserModelDefaultMethods {
+public class InMemoryUserAdapter extends UserModelDefaultMethods.Streams {
     private Long createdTimestamp = Time.currentTimeMillis();
     private boolean emailVerified;
     private boolean enabled;

server-spi/src/main/java/org/keycloak/models/GroupModel.java

@@ -68,11 +68,12 @@ public interface GroupModel extends RoleMapperModel {
      * @return list of all attribute values or empty list if there are not any values. Never return null
      */
     @Deprecated
-    default List<String> getAttribute(String name) {
+    List<String> getAttribute(String name);
-        return getAttributeStream(name).collect(Collectors.toList());
-    }
 
-    Stream<String> getAttributeStream(String name);
+    default Stream<String> getAttributeStream(String name) {
+        List<String> value = this.getAttribute(name);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     Map<String, List<String>> getAttributes();
 
@@ -80,11 +81,12 @@ public interface GroupModel extends RoleMapperModel {
     String getParentId();
 
     @Deprecated
-    default Set<GroupModel> getSubGroups() {
+    Set<GroupModel> getSubGroups();
-        return getSubGroupsStream().collect(Collectors.toSet());
-    }
 
-    Stream<GroupModel> getSubGroupsStream();
+    default Stream<GroupModel> getSubGroupsStream() {
+        Set<GroupModel> value = this.getSubGroups();
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * You must also call addChild on the parent group, addChild on RealmModel if there is no parent group
@@ -106,4 +108,29 @@ public interface GroupModel extends RoleMapperModel {
      * @param subGroup
      */
     void removeChild(GroupModel subGroup);
+
+    /**
+     * The {@link GroupModel.Streams} interface makes all collection-based methods in {@link GroupModel} default by providing
+     * implementations that delegate to the {@link Stream}-based variants instead of the other way around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends GroupModel, RoleMapperModel.Streams {
+        @Override
+        default List<String> getAttribute(String name) {
+            return this.getAttributeStream(name).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<String> getAttributeStream(String name);
+
+        @Override
+        default Set<GroupModel> getSubGroups() {
+            return this.getSubGroupsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<GroupModel> getSubGroupsStream();
+    }
 }

server-spi/src/main/java/org/keycloak/models/RoleMapperModel.java

@@ -32,15 +32,16 @@ public interface RoleMapperModel {
      * @deprecated Use {@link #getRealmRoleMappingsStream()} getRealmRoleMappingsStream} instead.
      */
     @Deprecated
-    default Set<RoleModel> getRealmRoleMappings() {
+    Set<RoleModel> getRealmRoleMappings();
-        return getRealmRoleMappingsStream().collect(Collectors.toSet());
-    }
 
     /**
      * Returns stream of realm roles that are directly set to this object.
      * @return stream of {@link RoleModel}
      */
-    Stream<RoleModel> getRealmRoleMappingsStream();
+    default Stream<RoleModel> getRealmRoleMappingsStream() {
+        Set<RoleModel> value = this.getRealmRoleMappings();
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Returns set of client roles that are directly set to this object for the given client.
@@ -49,16 +50,17 @@ public interface RoleMapperModel {
      * @deprecated Use {@link #getClientRoleMappingsStream(ClientModel)} getClientRoleMappingsStream} instead.
      */
     @Deprecated
-    default Set<RoleModel> getClientRoleMappings(ClientModel app) {
+    Set<RoleModel> getClientRoleMappings(ClientModel app);
-        return getClientRoleMappingsStream(app).collect(Collectors.toSet());
-    }
 
     /**
      * Returns stream of client roles that are directly set to this object for the given client.
      * @param app Client to get the roles for
      * @return stream of {@link RoleModel}
      */
-    Stream<RoleModel> getClientRoleMappingsStream(ClientModel app);
+    default Stream<RoleModel> getClientRoleMappingsStream(ClientModel app) {
+        Set<RoleModel> value = this.getClientRoleMappings(app);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Returns {@code true} if this object is directly or indirectly assigned the given role, {@code false} otherwise.
@@ -86,19 +88,53 @@ public interface RoleMapperModel {
      * @deprecated Use {@link #getRoleMappingsStream()} getRoleMappingsStream} instead.
      */
     @Deprecated
-    default Set<RoleModel> getRoleMappings() {
+    Set<RoleModel> getRoleMappings();
-        return getRoleMappingsStream().collect(Collectors.toSet());
-    }
 
     /**
      * Returns stream of all role (both realm all client) that are directly set to this object.
      * @return stream of {@link RoleModel}
      */
-    Stream<RoleModel> getRoleMappingsStream();
+    default Stream<RoleModel> getRoleMappingsStream() {
+        Set<RoleModel> value = this.getRoleMappings();
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Removes the given role mapping from this object.
      * @param role Role to remove
      */
     void deleteRoleMapping(RoleModel role);
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link RoleMapperModel} default by providing
+     * implementations that delegate to the {@link Stream}-based variants instead of the other way around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends RoleMapperModel {
+        @Override
+        default Set<RoleModel> getRealmRoleMappings() {
+            return this.getRealmRoleMappingsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<RoleModel> getRealmRoleMappingsStream();
+
+        @Override
+        default Set<RoleModel> getClientRoleMappings(ClientModel app) {
+            return this.getClientRoleMappingsStream(app).collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<RoleModel> getClientRoleMappingsStream(ClientModel app);
+
+        @Override
+        default Set<RoleModel> getRoleMappings() {
+            return this.getRoleMappingsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<RoleModel> getRoleMappingsStream();
+    }
 }

server-spi/src/main/java/org/keycloak/models/UserModel.java

@@ -94,17 +94,18 @@ public interface UserModel extends RoleMapperModel {
      * @deprecated Use {@link #getAttributeStream(String) getAttributeStream} instead.
      */
     @Deprecated
-    default List<String> getAttribute(String name) {
+    List<String> getAttribute(String name);
-        return this.getAttributeStream(name).collect(Collectors.toList());
-    }
 
     /**
      * Obtains all values associated with the specified attribute name.
      *
      * @param name the name of the attribute.
-     * @return a non-null {@code Stream} of attribute values.
+     * @return a non-null {@link Stream} of attribute values.
      */
-    Stream<String> getAttributeStream(final String name);
+    default Stream<String> getAttributeStream(final String name) {
+        List<String> value = this.getAttribute(name);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     Map<String, List<String>> getAttributes();
 
@@ -112,16 +113,17 @@ public interface UserModel extends RoleMapperModel {
      * @deprecated Use {@link #getRequiredActionsStream() getRequiredActionsStream} instead.
      */
     @Deprecated
-    default Set<String> getRequiredActions() {
+    Set<String> getRequiredActions();
-        return this.getRequiredActionsStream().collect(Collectors.toSet());
-    }
 
     /**
      * Obtains the names of required actions associated with the user.
      *
-     * @return a non-null {@code Stream} of required action names.
+     * @return a non-null {@link Stream} of required action names.
      */
-    Stream<String> getRequiredActionsStream();
+    default Stream<String> getRequiredActionsStream() {
+        Set<String> value = this.getRequiredActions();
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     void addRequiredAction(String action);
 
@@ -151,16 +153,17 @@ public interface UserModel extends RoleMapperModel {
      * @deprecated Use {@link #getGroupsStream() getGroupsStream} instead.
      */
     @Deprecated
-    default Set<GroupModel> getGroups() {
+    Set<GroupModel> getGroups();
-        return getGroupsStream().collect(Collectors.toSet());
-    }
 
     /**
      * Obtains the groups associated with the user.
      *
-     * @return a non-null {@code Stream} of groups.
+     * @return a non-null {@link Stream} of groups.
      */
-    Stream<GroupModel> getGroupsStream();
+    default Stream<GroupModel> getGroupsStream() {
+        Set<GroupModel> value = this.getGroups();
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * @deprecated Use {@link #getGroupsStream(String, Integer, Integer) getGroupsStream} instead.
@@ -230,4 +233,37 @@ public interface UserModel extends RoleMapperModel {
     enum RequiredAction {
         VERIFY_EMAIL, UPDATE_PROFILE, CONFIGURE_TOTP, UPDATE_PASSWORD, TERMS_AND_CONDITIONS
     }
+
+    /**
+     * The {@link UserModel.Streams} interface makes all collection-based methods in {@link UserModel} default by providing
+     * implementations that delegate to the {@link Stream}-based variants instead of the other way around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserModel, RoleMapperModel.Streams {
+        @Override
+        default List<String> getAttribute(String name) {
+            return this.getAttributeStream(name).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<String> getAttributeStream(final String name);
+
+        @Override
+        default Set<String> getRequiredActions() {
+            return this.getRequiredActionsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<String> getRequiredActionsStream();
+
+        @Override
+        default Set<GroupModel> getGroups() {
+            return this.getGroupsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<GroupModel> getGroupsStream();
+    }
 }

server-spi/src/main/java/org/keycloak/models/UserModelDefaultMethods.java

@@ -17,6 +17,8 @@
 
 package org.keycloak.models;
 
+import java.util.stream.Stream;
+
 /**
  * @author <a href="mailto:external.Martin.Idel@bosch.io">Martin Idel</a>
  * @version $Revision: 1 $
@@ -53,4 +55,13 @@ public abstract class UserModelDefaultMethods implements UserModel {
         email = email == null ? null : email.toLowerCase();
         setSingleAttribute(EMAIL, email);
     }
+
+    /**
+     * The {@link UserModelDefaultMethods.Streams} class extends the {@link UserModelDefaultMethods} abstract class and
+     * implements the {@link UserModel.Streams} interface, allowing subclasses to focus on the implementation of the
+     * {@link Stream}-based query methods and providing default implementations for the collections-based variants that
+     * delegate to their {@link Stream} counterparts.
+     */
+    public abstract static class Streams extends UserModelDefaultMethods implements UserModel.Streams {
+    }
 }

server-spi/src/main/java/org/keycloak/models/UserProvider.java

@@ -49,18 +49,19 @@ public interface UserProvider extends Provider,
      * @deprecated Use {@link #getFederatedIdentitiesStream(UserModel, RealmModel) getFederatedIdentitiesStream} instead.
      */
     @Deprecated
-    default Set<FederatedIdentityModel> getFederatedIdentities(UserModel user, RealmModel realm) {
+    Set<FederatedIdentityModel> getFederatedIdentities(UserModel user, RealmModel realm);
-        return this.getFederatedIdentitiesStream(user, realm).collect(Collectors.toSet());
-    }
 
     /**
      * Obtains the federated identities of the specified user.
      *
      * @param user a reference to the user.
      * @param realm a reference to the realm.
-     * @return a non-null {@code Stream} of federated identities associated with the user.
+     * @return a non-null {@link Stream} of federated identities associated with the user.
      */
-    Stream<FederatedIdentityModel> getFederatedIdentitiesStream(UserModel user, RealmModel realm);
+    default Stream<FederatedIdentityModel> getFederatedIdentitiesStream(UserModel user, RealmModel realm) {
+        Set<FederatedIdentityModel> value = this.getFederatedIdentities(user, realm);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     FederatedIdentityModel getFederatedIdentity(UserModel user, String socialProvider, RealmModel realm);
     UserModel getUserByFederatedIdentity(FederatedIdentityModel socialLink, RealmModel realm);
@@ -72,18 +73,19 @@ public interface UserProvider extends Provider,
      * @deprecated Use {@link #getConsentsStream(RealmModel, String) getConsentsStream} instead.
      */
     @Deprecated
-    default List<UserConsentModel> getConsents(RealmModel realm, String userId) {
+    List<UserConsentModel> getConsents(RealmModel realm, String userId);
-        return getConsentsStream(realm, userId).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the consents associated with the user identified by the specified {@code userId}.
      *
      * @param realm a reference to the realm.
      * @param userId the user identifier.
-     * @return a non-null {@code Stream} of consents associated with the user.
+     * @return a non-null {@link Stream} of consents associated with the user.
      */
-    Stream<UserConsentModel> getConsentsStream(RealmModel realm, String userId);
+    default Stream<UserConsentModel> getConsentsStream(RealmModel realm, String userId) {
+        List<UserConsentModel> value = this.getConsents(realm, userId);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     void updateConsent(RealmModel realm, String userId, UserConsentModel consent);
     boolean revokeConsentForClient(RealmModel realm, String userId, String clientInternalId);
@@ -97,26 +99,25 @@ public interface UserProvider extends Provider,
      * @deprecated Use {@link #getUsersStream(RealmModel, boolean) getUsersStream} instead.
      */
     @Deprecated
-    default List<UserModel> getUsers(RealmModel realm, boolean includeServiceAccounts) {
+    List<UserModel> getUsers(RealmModel realm, boolean includeServiceAccounts);
-        return this.getUsersStream(realm, includeServiceAccounts).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the users associated with the specified realm.
      *
      * @param realm a reference to the realm being used for the search.
      * @param includeServiceAccounts {@code true} if service accounts should be included in the result; {@code false} otherwise.
-     * @return a non-null {@code Stream} of users associated withe the realm.
+     * @return a non-null {@link Stream} of users associated withe the realm.
      */
-    Stream<UserModel> getUsersStream(RealmModel realm, boolean includeServiceAccounts);
+    default Stream<UserModel> getUsersStream(RealmModel realm, boolean includeServiceAccounts) {
+        List<UserModel> value = this.getUsers(realm, includeServiceAccounts);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * @deprecated Use {@link #getUsersStream(RealmModel, int, int, boolean) getUsersStream} instead.
      */
     @Deprecated
-    default List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults, boolean includeServiceAccounts) {
+    List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults, boolean includeServiceAccounts);
-        return this.getUsersStream(realm, firstResult, maxResults, includeServiceAccounts).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the users associated with the specified realm.
@@ -125,9 +126,12 @@ public interface UserProvider extends Provider,
      * @param firstResult first result to return. Ignored if negative.
      * @param maxResults maximum number of results to return. Ignored if negative.
      * @param includeServiceAccounts {@code true} if service accounts should be included in the result; {@code false} otherwise.
-     * @return a non-null {@code Stream} of users associated withe the realm.
+     * @return a non-null {@link Stream} of users associated withe the realm.
      */
-    Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults, boolean includeServiceAccounts);
+    default Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults, boolean includeServiceAccounts) {
+        List<UserModel> value = this.getUsers(realm, firstResult, maxResults, includeServiceAccounts);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * only used for local storage
@@ -168,4 +172,38 @@ public interface UserProvider extends Provider,
     void close();
 
     void preRemove(RealmModel realm, ComponentModel component);
+
+    interface Streams extends UserProvider, UserQueryProvider.Streams {
+        @Override
+        default Set<FederatedIdentityModel> getFederatedIdentities(UserModel user, RealmModel realm) {
+            return this.getFederatedIdentitiesStream(user, realm).collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<FederatedIdentityModel> getFederatedIdentitiesStream(UserModel user, RealmModel realm);
+
+        @Override
+        default List<UserConsentModel> getConsents(RealmModel realm, String userId) {
+            return this.getConsentsStream(realm, userId).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserConsentModel> getConsentsStream(RealmModel realm, String userId);
+
+        @Override
+        default List<UserModel> getUsers(RealmModel realm, boolean includeServiceAccounts) {
+            return this.getUsersStream(realm, includeServiceAccounts).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> getUsersStream(RealmModel realm, boolean includeServiceAccounts);
+
+        @Override
+        default List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults, boolean includeServiceAccounts) {
+            return this.getUsersStream(realm, firstResult, maxResults, includeServiceAccounts).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults, boolean includeServiceAccounts);
+    }
 }

server-spi/src/main/java/org/keycloak/models/cache/CachedUserModel.java

@@ -17,6 +17,7 @@
 package org.keycloak.models.cache;
 
 import org.keycloak.models.UserModel;
+import org.keycloak.models.UserProvider;
 
 import java.util.concurrent.ConcurrentMap;
 
@@ -56,4 +57,12 @@ public interface CachedUserModel extends UserModel {
      * @return
      */
     ConcurrentMap getCachedWith();
+
+    /**
+     * The {@link CachedUserModel.Streams} interface differs from {@link CachedUserModel} in that it extends the
+     * {@link UserModel.Streams} interface, allowing implementations of {@link CachedUserModel} to focus on the
+     * {@link java.util.stream.Stream}-based methods in the {@link UserModel} interface.
+     */
+    interface Streams extends CachedUserModel, UserModel.Streams {
+    }
 }

server-spi/src/main/java/org/keycloak/models/cache/UserCache.java

@@ -47,4 +47,12 @@ public interface UserCache extends UserProvider {
      *
      */
     void clear();
+
+    /**
+     * The {@link UserCache.Streams} interface differs from {@link UserCache} in that it extends the {@link UserProvider.Streams}
+     * interface, allowing implementations of {@link UserCache} to focus on the {@link java.util.stream.Stream}-based methods
+     * in the {@link UserProvider} interface.
+     */
+    interface Streams extends UserCache, UserProvider.Streams {
+    }
 }

server-spi/src/main/java/org/keycloak/models/utils/UserModelDelegate.java

@@ -33,7 +33,7 @@ import java.util.stream.Stream;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class UserModelDelegate implements UserModel {
+public class UserModelDelegate implements UserModel.Streams {
     protected UserModel delegate;
 
     public UserModelDelegate(UserModel delegate) {

server-spi/src/main/java/org/keycloak/storage/adapter/AbstractUserAdapter.java

@@ -30,8 +30,12 @@ import org.keycloak.models.utils.RoleUtils;
 import org.keycloak.storage.ReadOnlyException;
 import org.keycloak.storage.StorageId;
 
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 /**
@@ -59,8 +63,8 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
     }
 
     @Override
-    public Stream<String> getRequiredActionsStream() {
+    public Set<String> getRequiredActions() {
-        return Stream.empty();
+        return Collections.emptySet();
     }
 
     @Override
@@ -91,8 +95,8 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
      *
      * @return
      */
-    protected Stream<GroupModel> getGroupsInternal() {
+    protected Set<GroupModel> getGroupsInternal() {
-        return Stream.empty();
+        return Collections.emptySet();
     }
 
     /**
@@ -107,10 +111,11 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
     }
 
     @Override
-    public Stream<GroupModel> getGroupsStream() {
+    public Set<GroupModel> getGroups() {
-        Stream<GroupModel> groups = getGroupsInternal();
+        Set<GroupModel> set = new HashSet<>();
-        if (appendDefaultGroups()) groups = Stream.concat(groups, realm.getDefaultGroupsStream());
+        if (appendDefaultGroups()) set.addAll(realm.getDefaultGroupsStream().collect(Collectors.toSet()));
-        return groups;
+        set.addAll(getGroupsInternal());
+        return set;
     }
 
     @Override
@@ -127,23 +132,23 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
 
     @Override
     public boolean isMemberOf(GroupModel group) {
-        return RoleUtils.isMember(getGroupsStream(), group);
+        return RoleUtils.isMember(getGroups().stream(), group);
     }
 
     @Override
-    public Stream<RoleModel> getRealmRoleMappingsStream() {
+    public Set<RoleModel> getRealmRoleMappings() {
-        return getRoleMappingsStream().filter(RoleUtils::isRealmRole);
+        return getRoleMappings().stream().filter(RoleUtils::isRealmRole).collect(Collectors.toSet());
     }
 
     @Override
-    public Stream<RoleModel> getClientRoleMappingsStream(ClientModel app) {
+    public Set<RoleModel> getClientRoleMappings(ClientModel app) {
-        return getRoleMappingsStream().filter(r -> RoleUtils.isClientRole(r, app));
+        return getRoleMappings().stream().filter(r -> RoleUtils.isClientRole(r, app)).collect(Collectors.toSet());
     }
 
     @Override
     public boolean hasRole(RoleModel role) {
-        return RoleUtils.hasRole(getRoleMappingsStream(), role)
+        return RoleUtils.hasRole(getRoleMappings().stream(), role)
-          || RoleUtils.hasRoleFromGroup(getGroupsStream(), role, true);
+          || RoleUtils.hasRoleFromGroup(getGroups().stream(), role, true);
     }
 
     @Override
@@ -163,15 +168,16 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
         return true;
     }
 
-    protected Stream<RoleModel> getRoleMappingsInternal() {
+    protected Set<RoleModel> getRoleMappingsInternal() {
-        return Stream.empty();
+        return Collections.emptySet();
     }
 
     @Override
-    public Stream<RoleModel> getRoleMappingsStream() {
+    public Set<RoleModel> getRoleMappings() {
-        Stream<RoleModel> roleMappings = getRoleMappingsInternal();
+        Set<RoleModel> set = new HashSet<>();
-        if (appendDefaultRolesToRoleMappings()) return Stream.concat(roleMappings, DefaultRoles.getDefaultRoles(realm));
+        if (appendDefaultRolesToRoleMappings()) set.addAll(DefaultRoles.getDefaultRoles(realm).collect(Collectors.toSet()));
-        return roleMappings;
+        set.addAll(getRoleMappingsInternal());
+        return set;
     }
 
 
@@ -300,11 +306,11 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
     }
 
     @Override
-    public Stream<String> getAttributeStream(String name) {
+    public List<String> getAttribute(String name) {
         if (name.equals(UserModel.USERNAME)) {
-            return Stream.of(getUsername());
+            return Collections.singletonList(getUsername());
         }
-        return Stream.empty();
+        return Collections.emptyList();
     }
 
     @Override
@@ -365,4 +371,100 @@ public abstract class AbstractUserAdapter extends UserModelDefaultMethods {
         return getId().hashCode();
     }
 
+    /**
+     * The {@link AbstractUserAdapter.Streams} class extends the {@link AbstractUserAdapter} abstract class and implements
+     * the {@link UserModel.Streams} interface, allowing subclasses to focus on the implementation of the {@link Stream}-based
+     * query methods and providing default implementations for the collections-based variants that delegate to their
+     * {@link Stream} counterparts.
+     */
+    public abstract static class Streams extends AbstractUserAdapter implements UserModel.Streams {
+
+        public Streams(final KeycloakSession session, final RealmModel realm, final ComponentModel storageProviderModel) {
+            super(session, realm, storageProviderModel);
+        }
+
+        @Override
+        public Set<String> getRequiredActions() {
+            return this.getRequiredActionsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<String> getRequiredActionsStream() {
+            return Stream.empty();
+        }
+
+        @Override
+        public List<String> getAttribute(String name) {
+            return this.getAttributeStream(name).collect(Collectors.toList());
+        }
+
+        @Override
+        public Stream<String> getAttributeStream(String name) {
+            if (name.equals(UserModel.USERNAME)) {
+                return Stream.of(getUsername());
+            }
+            return Stream.empty();
+        }
+
+        // group-related methods.
+
+
+        @Override
+        public Set<GroupModel> getGroups() {
+            return this.getGroupsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<GroupModel> getGroupsStream() {
+            Stream<GroupModel> groups = getGroupsInternal().stream();
+            if (appendDefaultGroups()) groups = Stream.concat(groups, realm.getDefaultGroupsStream());
+            return groups;
+        }
+
+        @Override
+        public boolean isMemberOf(GroupModel group) {
+            return RoleUtils.isMember(this.getGroupsStream(), group);
+        }
+
+        // role-related methods.
+
+
+        @Override
+        public Set<RoleModel> getRealmRoleMappings() {
+            return this.getRealmRoleMappingsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<RoleModel> getRealmRoleMappingsStream() {
+            return getRoleMappingsStream().filter(RoleUtils::isRealmRole);
+        }
+
+        @Override
+        public Set<RoleModel> getClientRoleMappings(ClientModel app) {
+            return this.getClientRoleMappingsStream(app).collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<RoleModel> getClientRoleMappingsStream(ClientModel app) {
+            return getRoleMappingsStream().filter(r -> RoleUtils.isClientRole(r, app));
+        }
+
+        @Override
+        public Set<RoleModel> getRoleMappings() {
+            return this.getRoleMappingsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<RoleModel> getRoleMappingsStream() {
+            Stream<RoleModel> roleMappings = getRoleMappingsInternal().stream();
+            if (appendDefaultRolesToRoleMappings()) return Stream.concat(roleMappings, DefaultRoles.getDefaultRoles(realm));
+            return roleMappings;
+        }
+
+        @Override
+        public boolean hasRole(RoleModel role) {
+            return RoleUtils.hasRole(this.getRoleMappingsStream(), role)
+                    || RoleUtils.hasRoleFromGroup(this.getGroupsStream(), role, true);
+        }
+    }
 }

server-spi/src/main/java/org/keycloak/storage/adapter/AbstractUserAdapterFederatedStorage.java

@@ -30,8 +30,12 @@ import org.keycloak.models.utils.RoleUtils;
 import org.keycloak.storage.StorageId;
 import org.keycloak.storage.federated.UserFederatedStorageProvider;
 
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 /**
@@ -68,8 +72,8 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
     }
 
     @Override
-    public Stream<String> getRequiredActionsStream() {
+    public Set<String> getRequiredActions() {
-        return getFederatedStorage().getRequiredActionsStream(realm, this.getId());
+        return getFederatedStorage().getRequiredActions(realm, this.getId());
     }
 
     @Override
@@ -100,8 +104,8 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
      *
      * @return
      */
-    protected Stream<GroupModel> getGroupsInternal() {
+    protected Set<GroupModel> getGroupsInternal() {
-        return Stream.empty();
+        return Collections.emptySet();
     }
 
     /**
@@ -124,10 +128,11 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
      * @return
      */
     @Override
-    public Stream<GroupModel> getGroupsStream() {
+    public Set<GroupModel> getGroups() {
-        Stream<GroupModel> groups = getFederatedStorage().getGroupsStream(realm, this.getId());
+        Set<GroupModel> set = new HashSet<>(getFederatedStorage().getGroups(realm, this.getId()));
-        if (appendDefaultGroups()) groups = Stream.concat(groups, realm.getDefaultGroupsStream());
+        if (appendDefaultGroups()) set.addAll(realm.getDefaultGroupsStream().collect(Collectors.toSet()));
-        return Stream.concat(groups, getGroupsInternal());
+        set.addAll(getGroupsInternal());
+        return set;
     }
 
     @Override
@@ -144,7 +149,7 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
 
     @Override
     public boolean isMemberOf(GroupModel group) {
-        return RoleUtils.isMember(getGroupsStream(), group);
+        return RoleUtils.isMember(getGroups().stream(), group);
     }
 
     /**
@@ -156,8 +161,8 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
      * @return
      */
     @Override
-    public Stream<RoleModel> getRealmRoleMappingsStream() {
+    public Set<RoleModel> getRealmRoleMappings() {
-        return getRoleMappingsStream().filter(RoleUtils::isRealmRole);
+        return this.getRoleMappings().stream().filter(RoleUtils::isRealmRole).collect(Collectors.toSet());
     }
 
     /**
@@ -169,14 +174,15 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
      * @return
      */
     @Override
-    public Stream<RoleModel> getClientRoleMappingsStream(ClientModel app) {
+    public Set<RoleModel> getClientRoleMappings(ClientModel app) {
-        return getRoleMappingsStream().filter(r -> RoleUtils.isClientRole(r, app));
+        return getRoleMappings().stream().filter(r -> RoleUtils.isClientRole(r, app)).collect(Collectors.toSet());
     }
 
+
     @Override
     public boolean hasRole(RoleModel role) {
-        return RoleUtils.hasRole(getRoleMappingsStream(), role)
+        return RoleUtils.hasRole(getRoleMappings().stream(), role)
-          || RoleUtils.hasRoleFromGroup(getGroupsStream(), role, true);
+          || RoleUtils.hasRoleFromGroup(getGroups().stream(), role, true);
     }
 
     @Override
@@ -196,8 +202,8 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
         return true;
     }
 
-    protected Stream<RoleModel> getRoleMappingsInternal() {
+    protected Set<RoleModel> getRoleMappingsInternal() {
-        return Stream.empty();
+        return Collections.emptySet();
     }
 
     /**
@@ -208,14 +214,15 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
      * @return
      */
     @Override
-    public Stream<RoleModel> getRoleMappingsStream() {
+    public Set<RoleModel> getRoleMappings() {
-        Stream<RoleModel> roleMappings = getFederatedRoleMappings();
+        Set<RoleModel> set = new HashSet<>(getFederatedRoleMappings());
-        if (appendDefaultRolesToRoleMappings()) roleMappings = Stream.concat(roleMappings, DefaultRoles.getDefaultRoles(realm));
+        if (appendDefaultRolesToRoleMappings()) set.addAll(DefaultRoles.getDefaultRoles(realm).collect(Collectors.toSet()));
-        return Stream.concat(roleMappings, getRoleMappingsInternal());
+        set.addAll(getRoleMappingsInternal());
+        return set;
     }
 
-    protected Stream<RoleModel> getFederatedRoleMappings() {
+    protected Set<RoleModel> getFederatedRoleMappings() {
-        return getFederatedStorage().getRoleMappingsStream(realm, this.getId());
+        return getFederatedStorage().getRoleMappings(realm, this.getId());
     }
 
     @Override
@@ -357,15 +364,15 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
     }
 
     @Override
-    public Stream<String> getAttributeStream(String name) {
+    public List<String> getAttribute(String name) {
         if (UserModel.USERNAME.equals(name)) {
-            return Stream.of(getUsername());
+            return Collections.singletonList(getUsername());
         }
         List<String> result = getFederatedStorage().getAttributes(realm, this.getId()).get(mapAttribute(name));
-        return (result == null) ? Stream.empty() : result.stream();
+        return (result == null) ? Collections.emptyList() : result;
     }
 
-    private String mapAttribute(String attributeName) {
+    protected String mapAttribute(String attributeName) {
         if (UserModel.FIRST_NAME.equals(attributeName)) {
             return FIRST_NAME_ATTRIBUTE;
         } else if (UserModel.LAST_NAME.equals(attributeName)) {
@@ -409,4 +416,101 @@ public abstract class AbstractUserAdapterFederatedStorage extends UserModelDefau
         return getId().hashCode();
     }
 
+    /**
+     * The {@link AbstractUserAdapterFederatedStorage.Streams} class extends the {@link AbstractUserAdapterFederatedStorage}
+     * abstract class and implements the {@link UserModel.Streams} interface, allowing subclasses to focus on the implementation
+     * of the {@link Stream}-based query methods and providing default implementations for the collections-based variants
+     * that delegate to their {@link Stream} counterparts.
+     */
+    public abstract static class Streams extends AbstractUserAdapterFederatedStorage implements UserModel.Streams {
+
+        public Streams(final KeycloakSession session, final RealmModel realm, final ComponentModel storageProviderModel) {
+            super(session, realm, storageProviderModel);
+        }
+
+        // user-related methods.
+
+        @Override
+        public Set<String> getRequiredActions() {
+            return this.getRequiredActionsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<String> getRequiredActionsStream() {
+            return super.getFederatedStorage().getRequiredActionsStream(super.realm, super.getId());
+        }
+
+        @Override
+        public List<String> getAttribute(String name) {
+            return this.getAttributeStream(name).collect(Collectors.toList());
+        }
+
+        @Override
+        public Stream<String> getAttributeStream(String name) {
+            if (UserModel.USERNAME.equals(name)) {
+                return Stream.of(getUsername());
+            }
+            List<String> result = super.getFederatedStorage().getAttributes(realm, this.getId()).get(super.mapAttribute(name));
+            return (result == null) ? Stream.empty() : result.stream();
+        }
+
+        // group-related methods.
+
+        @Override
+        public Set<GroupModel> getGroups() {
+            return this.getGroupsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<GroupModel> getGroupsStream() {
+            Stream<GroupModel> groups = getFederatedStorage().getGroupsStream(realm, this.getId());
+            if (appendDefaultGroups()) groups = Stream.concat(groups, realm.getDefaultGroupsStream());
+            return Stream.concat(groups, getGroupsInternal().stream());
+        }
+
+        @Override
+        public boolean isMemberOf(GroupModel group) {
+            return RoleUtils.isMember(this.getGroupsStream(), group);
+        }
+
+        // role-related methods.
+
+        @Override
+        public Set<RoleModel> getRealmRoleMappings() {
+            return this.getRealmRoleMappingsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<RoleModel> getRealmRoleMappingsStream() {
+            return getRoleMappingsStream().filter(RoleUtils::isRealmRole);
+        }
+
+        @Override
+        public Set<RoleModel> getClientRoleMappings(ClientModel app) {
+            return this.getClientRoleMappingsStream(app).collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<RoleModel> getClientRoleMappingsStream(ClientModel app) {
+            return getRoleMappingsStream().filter(r -> RoleUtils.isClientRole(r, app));
+        }
+
+        @Override
+        public Set<RoleModel> getRoleMappings() {
+            return this.getRoleMappingsStream().collect(Collectors.toSet());
+        }
+
+        @Override
+        public Stream<RoleModel> getRoleMappingsStream() {
+            Stream<RoleModel> roleMappings = getFederatedRoleMappings().stream();
+            if (appendDefaultRolesToRoleMappings()) roleMappings = Stream.concat(roleMappings, DefaultRoles.getDefaultRoles(realm));
+            return Stream.concat(roleMappings, getRoleMappingsInternal().stream());
+        }
+
+        @Override
+        public boolean hasRole(RoleModel role) {
+            return RoleUtils.hasRole(this.getRoleMappingsStream(), role)
+                    || RoleUtils.hasRoleFromGroup(this.getGroupsStream(), role, true);
+        }
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserAttributeFederatedStorage.java

@@ -37,9 +37,7 @@ public interface UserAttributeFederatedStorage {
      * @deprecated Use {@link #getUsersByUserAttributeStream(RealmModel, String, String) getUsersByUserAttributeStream} instead.
      */
     @Deprecated
-    default List<String> getUsersByUserAttribute(RealmModel realm, String name, String value) {
+    List<String> getUsersByUserAttribute(RealmModel realm, String name, String value);
-        return this.getUsersByUserAttributeStream(realm, name, value).collect(Collectors.toList());
-    }
 
     /**
      * Searches for federated users that have an attribute with the specified {@code name} and {@code value}.
@@ -47,7 +45,29 @@ public interface UserAttributeFederatedStorage {
      * @param realm a reference to the realm.
      * @param name the attribute name.
      * @param value the attribute value.
-     * @return a non-null {@code Stream} of users that match the search criteria.
+     * @return a non-null {@link Stream} of users that match the search criteria.
      */
-    Stream<String> getUsersByUserAttributeStream(RealmModel realm, String name, String value);
+    default Stream<String> getUsersByUserAttributeStream(RealmModel realm, String name, String value) {
+        List<String> users = this.getUsersByUserAttribute(realm, name, value);
+        return users != null ? users.stream() : Stream.empty();
+    }
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserAttributeFederatedStorage}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserAttributeFederatedStorage {
+
+        @Override
+        default List<String> getUsersByUserAttribute(RealmModel realm, String name, String value) {
+            return this.getUsersByUserAttributeStream(realm, name, value).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<String> getUsersByUserAttributeStream(RealmModel realm, String name, String value);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserBrokerLinkFederatedStorage.java

@@ -39,18 +39,37 @@ public interface UserBrokerLinkFederatedStorage {
      * @deprecated Use {@link #getFederatedIdentitiesStream(String, RealmModel) getFederatedIdentitiesStream} instead.
      */
     @Deprecated
-    default Set<FederatedIdentityModel> getFederatedIdentities(String userId, RealmModel realm) {
+    Set<FederatedIdentityModel> getFederatedIdentities(String userId, RealmModel realm);
-        return this.getFederatedIdentitiesStream(userId, realm).collect(Collectors.toSet());
-    }
 
     /**
      * Obtains the identities of the federated user identified by {@code userId}.
      *
      * @param userId the user identifier.
      * @param realm a reference to the realm.
-     * @return a non-null {@code Stream} of federated identities associated with the user.
+     * @return a non-null {@link Stream} of federated identities associated with the user.
      */
-    Stream<FederatedIdentityModel> getFederatedIdentitiesStream(String userId, RealmModel realm);
+    default Stream<FederatedIdentityModel> getFederatedIdentitiesStream(String userId, RealmModel realm) {
+        Set<FederatedIdentityModel> value = this.getFederatedIdentities(userId, realm);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     FederatedIdentityModel getFederatedIdentity(String userId, String socialProvider, RealmModel realm);
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserBrokerLinkFederatedStorage}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserBrokerLinkFederatedStorage {
+        @Override
+        default Set<FederatedIdentityModel> getFederatedIdentities(String userId, RealmModel realm) {
+            return this.getFederatedIdentitiesStream(userId, realm).collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<FederatedIdentityModel> getFederatedIdentitiesStream(String userId, RealmModel realm);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserConsentFederatedStorage.java

@@ -35,19 +35,38 @@ public interface UserConsentFederatedStorage {
      * @deprecated Use {@link #getConsentsStream(RealmModel, String) getConsentsStream} instead.
      */
     @Deprecated
-    default List<UserConsentModel> getConsents(RealmModel realm, String userId) {
+    List<UserConsentModel> getConsents(RealmModel realm, String userId);
-        return this.getConsentsStream(realm, userId).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the consents associated with the federated user identified by {@code userId}.
      *
      * @param realm a reference to the realm.
      * @param userId the user identifier.
-     * @return a non-null {@code Stream} of consents associated with the user.
+     * @return a non-null {@link Stream} of consents associated with the user.
      */
-    Stream<UserConsentModel> getConsentsStream(RealmModel realm, String userId);
+    default Stream<UserConsentModel> getConsentsStream(RealmModel realm, String userId) {
+        List<UserConsentModel> value = this.getConsents(realm, userId);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     void updateConsent(RealmModel realm, String userId, UserConsentModel consent);
     boolean revokeConsentForClient(RealmModel realm, String userId, String clientInternalId);
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserConsentFederatedStorage}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserConsentFederatedStorage {
+        @Override
+        default List<UserConsentModel> getConsents(RealmModel realm, String userId) {
+            return this.getConsentsStream(realm, userId).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserConsentModel> getConsentsStream(RealmModel realm, String userId);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserFederatedStorageProvider.java

@@ -49,9 +49,7 @@ public interface UserFederatedStorageProvider extends Provider,
      * @deprecated Use {@link #getStoredUsersStream(RealmModel, int, int) getStoredUsersStream} instead.
      */
     @Deprecated
-    default List<String> getStoredUsers(RealmModel realm, int first, int max) {
+    List<String> getStoredUsers(RealmModel realm, int first, int max);
-        return getStoredUsersStream(realm, first, max).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the ids of all federated users in the realm.
@@ -59,9 +57,12 @@ public interface UserFederatedStorageProvider extends Provider,
      * @param realm a reference to the realm.
      * @param first first result to return. Ignored if negative.
      * @param max maximum number of results to return. Ignored if negative.
-     * @return a non-null {@code Stream} of federated user ids.
+     * @return a non-null {@link Stream} of federated user ids.
      */
-    Stream<String> getStoredUsersStream(RealmModel realm, int first, int max);
+    default Stream<String> getStoredUsersStream(RealmModel realm, int first, int max) {
+        List<String> value = this.getStoredUsers(realm, first, max);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     int getStoredUsersCount(RealmModel realm);
 
@@ -80,4 +81,30 @@ public interface UserFederatedStorageProvider extends Provider,
     void preRemove(RealmModel realm, UserModel user);
 
     void preRemove(RealmModel realm, ComponentModel model);
+
+    /**
+     * The {@link UserFederatedStorageProvider.Streams} interface makes all collection-based methods in {@link UserFederatedStorageProvider}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserFederatedStorageProvider,
+            UserAttributeFederatedStorage.Streams,
+            UserBrokerLinkFederatedStorage.Streams,
+            UserConsentFederatedStorage.Streams,
+            UserFederatedUserCredentialStore.Streams,
+            UserGroupMembershipFederatedStorage.Streams,
+            UserRequiredActionsFederatedStorage.Streams,
+            UserRoleMappingsFederatedStorage.Streams {
+
+        @Override
+        default List<String> getStoredUsers(RealmModel realm, int first, int max) {
+            return this.getStoredUsersStream(realm, first, max).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<String> getStoredUsersStream(RealmModel realm, int first, int max);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserFederatedUserCredentialStore.java

@@ -38,26 +38,25 @@ public interface UserFederatedUserCredentialStore extends Provider {
      * @deprecated Use {@link #getStoredCredentialsStream(RealmModel, String) getStoredCredentialsStream} instead.
      */
     @Deprecated
-    default List<CredentialModel> getStoredCredentials(RealmModel realm, String userId) {
+    List<CredentialModel> getStoredCredentials(RealmModel realm, String userId);
-        return this.getStoredCredentialsStream(realm, userId).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the credentials associated with the federated user identified by {@code userId}.
      *
      * @param realm a reference to the realm.
      * @param userId the user identifier.
-     * @return a non-null {@code Stream} of credentials.
+     * @return a non-null {@link Stream} of credentials.
      */
-    Stream<CredentialModel> getStoredCredentialsStream(RealmModel realm, String userId);
+    default Stream<CredentialModel> getStoredCredentialsStream(RealmModel realm, String userId) {
+        List<CredentialModel> value = this.getStoredCredentials(realm, userId);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * @deprecated Use {@link #getStoredCredentialsByTypeStream(RealmModel, String, String) getStoredCredentialsByTypeStream} instead.
      */
     @Deprecated
-    default List<CredentialModel> getStoredCredentialsByType(RealmModel realm, String userId, String type) {
+    List<CredentialModel> getStoredCredentialsByType(RealmModel realm, String userId, String type);
-        return this.getStoredCredentialsByTypeStream(realm, userId, type).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the credentials of type {@code type} that are associated with the federated user identified by {@code userId}.
@@ -65,9 +64,38 @@ public interface UserFederatedUserCredentialStore extends Provider {
      * @param realm a reference to the realm.
      * @param userId the user identifier.
      * @param type the credential type.
-     * @return a non-null {@code Stream} of credentials.
+     * @return a non-null {@link Stream} of credentials.
      */
-    Stream<CredentialModel> getStoredCredentialsByTypeStream(RealmModel realm, String userId, String type);
+    default Stream<CredentialModel> getStoredCredentialsByTypeStream(RealmModel realm, String userId, String type) {
+        List<CredentialModel> value = this.getStoredCredentialsByType(realm, userId, type);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     CredentialModel getStoredCredentialByNameAndType(RealmModel realm, String userId, String name, String type);
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserFederatedUserCredentialStore}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserFederatedUserCredentialStore {
+        @Override
+        default List<CredentialModel> getStoredCredentials(RealmModel realm, String userId) {
+            return this.getStoredCredentialsStream(realm, userId).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<CredentialModel> getStoredCredentialsStream(RealmModel realm, String userId);
+
+        @Override
+        default List<CredentialModel> getStoredCredentialsByType(RealmModel realm, String userId, String type) {
+            return this.getStoredCredentialsByTypeStream(realm, userId, type).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<CredentialModel> getStoredCredentialsByTypeStream(RealmModel realm, String userId, String type);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserGroupMembershipFederatedStorage.java

@@ -29,12 +29,24 @@ import java.util.stream.Stream;
  * @version $Revision: 1 $
  */
 public interface UserGroupMembershipFederatedStorage {
-    @Deprecated
-    default Set<GroupModel> getGroups(RealmModel realm, String userId) {
-        return getGroupsStream(realm, userId).collect(Collectors.toSet());
-    }
 
-    Stream<GroupModel> getGroupsStream(RealmModel realm, String userId);
+    /**
+     * @deprecated Use {@link #getGroupsStream(RealmModel, String) getGroupsStream} instead.
+     */
+    @Deprecated
+    Set<GroupModel> getGroups(RealmModel realm, String userId);
+
+    /**
+     * Obtains the groups associated with the federated user.
+     *
+     * @param realm a reference to the realm.
+     * @param userId the user identifier.
+     * @return a non-null {@code Stream} of groups.
+     */
+    default Stream<GroupModel> getGroupsStream(RealmModel realm, String userId) {
+        Set<GroupModel> value = this.getGroups(realm, userId);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     void joinGroup(RealmModel realm, String userId, GroupModel group);
     void leaveGroup(RealmModel realm, String userId, GroupModel group);
@@ -43,9 +55,7 @@ public interface UserGroupMembershipFederatedStorage {
      * @deprecated Use {@link #getMembershipStream(RealmModel, GroupModel, int, int) getMembershipStream} instead.
      */
     @Deprecated
-    default List<String> getMembership(RealmModel realm, GroupModel group, int firstResult, int max) {
+    List<String> getMembership(RealmModel realm, GroupModel group, int firstResult, int max);
-        return this.getMembershipStream(realm, group, firstResult, max).collect(Collectors.toList());
-    }
 
     /**
      * Obtains the federated users that are members of the given {@code group} in the specified {@code realm}.
@@ -56,6 +66,34 @@ public interface UserGroupMembershipFederatedStorage {
      * @param max maximum number of results to return. Ignored if negative.
      * @return a non-null {@code Stream} of federated user ids that are members of the group in the realm.
      */
-    Stream<String> getMembershipStream(RealmModel realm, GroupModel group, int firstResult, int max);
+    default Stream<String> getMembershipStream(RealmModel realm, GroupModel group, int firstResult, int max) {
+        List<String> value = this.getMembership(realm, group, firstResult, max);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserGroupMembershipFederatedStorage}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserGroupMembershipFederatedStorage {
+        @Override
+        default Set<GroupModel> getGroups(RealmModel realm, String userId) {
+            return getGroupsStream(realm, userId).collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<GroupModel> getGroupsStream(RealmModel realm, String userId);
+
+        @Override
+        default List<String> getMembership(RealmModel realm, GroupModel group, int firstResult, int max) {
+            return this.getMembershipStream(realm, group, firstResult, max).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<String> getMembershipStream(RealmModel realm, GroupModel group, int firstResult, int max);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserRequiredActionsFederatedStorage.java

@@ -32,18 +32,38 @@ public interface UserRequiredActionsFederatedStorage {
      * @deprecated Use {@link #getRequiredActionsStream(RealmModel, String) getRequiredActionsStream} instead.
      */
     @Deprecated
-    default Set<String> getRequiredActions(RealmModel realm, String userId) {
+    Set<String> getRequiredActions(RealmModel realm, String userId);
-        return this.getRequiredActionsStream(realm, userId).collect(Collectors.toSet());
+
-    }
     /**
      * Obtains the names of required actions associated with the federated user identified by {@code userId}.
      *
      * @param realm a reference to the realm.
      * @param userId the user identifier.
-     * @return a non-null {@code Stream} of required action names.
+     * @return a non-null {@link Stream} of required action names.
      */
-    Stream<String> getRequiredActionsStream(RealmModel realm, String userId);
+    default Stream<String> getRequiredActionsStream(RealmModel realm, String userId) {
+        Set<String> value = this.getRequiredActions(realm, userId);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     void addRequiredAction(RealmModel realm, String userId, String action);
     void removeRequiredAction(RealmModel realm, String userId, String action);
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserRequiredActionsFederatedStorage}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserRequiredActionsFederatedStorage {
+        @Override
+        default Set<String> getRequiredActions(RealmModel realm, String userId) {
+            return this.getRequiredActionsStream(realm, userId).collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<String> getRequiredActionsStream(RealmModel realm, String userId);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/federated/UserRoleMappingsFederatedStorage.java

@@ -29,15 +29,13 @@ import java.util.stream.Stream;
  */
 public interface UserRoleMappingsFederatedStorage {
 
-    void grantRole(RealmModel realm, String userId, RoleModel role);
-
     /**
      * @deprecated Use {@link #getRoleMappingsStream(RealmModel, String) getRoleMappingsStream} instead.
      */
     @Deprecated
-    default Set<RoleModel> getRoleMappings(RealmModel realm,String userId) {
+    Set<RoleModel> getRoleMappings(RealmModel realm,String userId);
-        return getRoleMappingsStream(realm, userId).collect(Collectors.toSet());
+
-    }
+    void grantRole(RealmModel realm, String userId, RoleModel role);
 
     /**
      * Obtains the roles associated with the federated user identified by {@code userId}.
@@ -46,7 +44,28 @@ public interface UserRoleMappingsFederatedStorage {
      * @param userId the user identifier.
      * @return a non-null {@code Stream} of roles.
      */
-    Stream<RoleModel> getRoleMappingsStream(RealmModel realm, String userId);
+    default Stream<RoleModel> getRoleMappingsStream(RealmModel realm, String userId) {
+        Set<RoleModel> value = this.getRoleMappings(realm, userId);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     void deleteRoleMapping(RealmModel realm, String userId, RoleModel role);
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserRoleMappingsFederatedStorage}
+     * default by providing implementations that delegate to the {@link Stream}-based variants instead of the other way
+     * around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserRoleMappingsFederatedStorage {
+        @Override
+        default Set<RoleModel> getRoleMappings(RealmModel realm, String userId) {
+            return getRoleMappingsStream(realm, userId).collect(Collectors.toSet());
+        }
+
+        @Override
+        Stream<RoleModel> getRoleMappingsStream(RealmModel realm, String userId);
+    }
 }

server-spi/src/main/java/org/keycloak/storage/user/UserQueryProvider.java

@@ -141,25 +141,23 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #getUsersStream(RealmModel) getUsersStream} instead.
      */
     @Deprecated
-    default List<UserModel> getUsers(RealmModel realm) {
+    List<UserModel> getUsers(RealmModel realm);
-        return this.getUsersStream(realm).collect(Collectors.toList());
-    }
-
     /**
      * Searches all users in the realm.
      *
      * @param realm a reference to the realm.
-     * @return a non-null {@code Stream} of users.
+     * @return a non-null {@link Stream} of users.
      */
-    Stream<UserModel> getUsersStream(RealmModel realm);
+    default Stream<UserModel> getUsersStream(RealmModel realm) {
+        List<UserModel> value = this.getUsers(realm);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * @deprecated Use {@link #getUsersStream(RealmModel, int, int) getUsersStream} instead.
      */
     @Deprecated
-    default List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults) {
+    List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults);
-        return this.getUsersStream(realm, firstResult, maxResults).collect(Collectors.toList());
-    }
 
     /**
      * Searches all users in the realm, starting from the {@code firstResult} and containing at most {@code maxResults}.
@@ -167,9 +165,12 @@ public interface UserQueryProvider {
      * @param realm a reference to the realm.
      * @param firstResult first result to return. Ignored if negative.
      * @param maxResults maximum number of results to return. Ignored if negative.
-     * @return a non-null {@code Stream} of users.
+     * @return a non-null {@link Stream} of users.
      */
-    Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults);
+    default Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults) {
+        List<UserModel> value = this.getUsers(realm, firstResult, maxResults);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Search for users with username, email or first + last name that is like search string.
@@ -184,9 +185,7 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #searchForUserStream(String, RealmModel) searchForUserStream} instead.
      */
     @Deprecated
-    default List<UserModel> searchForUser(String search, RealmModel realm) {
+    List<UserModel> searchForUser(String search, RealmModel realm);
-        return this.searchForUserStream(search, realm).collect(Collectors.toList());
-    }
 
     /**
      * Searches for users with username, email or first + last name that is like search string.  If possible, implementations
@@ -196,9 +195,12 @@ public interface UserQueryProvider {
      *
      * @param search case sensitive search string.
      * @param realm a reference to the realm.
-     * @return a non-null {@code Stream} of users that match the search string.
+     * @return a non-null {@link Stream} of users that match the search string.
      */
-    Stream<UserModel> searchForUserStream(String search, RealmModel realm);
+    default Stream<UserModel> searchForUserStream(String search, RealmModel realm) {
+        List<UserModel> value = this.searchForUser(search, realm);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Search for users with username, email or first + last name that is like search string.
@@ -215,9 +217,7 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #searchForUserStream(String, RealmModel, int, int) searchForUserStream} instead.
      */
     @Deprecated
-    default List<UserModel> searchForUser(String search, RealmModel realm, int firstResult, int maxResults) {
+    List<UserModel> searchForUser(String search, RealmModel realm, int firstResult, int maxResults);
-        return this.searchForUserStream(search, realm, firstResult, maxResults).collect(Collectors.toList());
-    }
 
     /**
      * Searches for users with username, email or first + last name that is like search string. If possible, implementations
@@ -229,9 +229,12 @@ public interface UserQueryProvider {
      * @param realm a reference to the realm.
      * @param firstResult first result to return. Ignored if negative.
      * @param maxResults maximum number of results to return. Ignored if negative.
-     * @return a non-null {@code Stream} of users that match the search criteria.
+     * @return a non-null {@link Stream} of users that match the search criteria.
      */
-    Stream<UserModel> searchForUserStream(String search, RealmModel realm, int firstResult, int maxResults);
+    default Stream<UserModel> searchForUserStream(String search, RealmModel realm, int firstResult, int maxResults) {
+        List<UserModel> value = this.searchForUser(search, realm, firstResult, maxResults);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Search for user by parameter.  Valid parameters are:
@@ -251,9 +254,7 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #searchForUserStream(Map, RealmModel) searchForUserStream} instead.
      */
     @Deprecated
-    default List<UserModel> searchForUser(Map<String, String> params, RealmModel realm) {
+    List<UserModel> searchForUser(Map<String, String> params, RealmModel realm);
-        return this.searchForUserStream(params, realm).collect(Collectors.toList());
-    }
 
     /**
      * Searches for user by parameter. If possible, implementations should treat the parameter values as partial match patterns
@@ -269,9 +270,12 @@ public interface UserQueryProvider {
      *
      * @param params a map containing the search parameters.
      * @param realm a reference to the realm.
-     * @return a non-null {@code Stream} of users that match the search parameters.
+     * @return a non-null {@link Stream} of users that match the search parameters.
      */
-    Stream<UserModel> searchForUserStream(Map<String, String> params, RealmModel realm);
+    default Stream<UserModel> searchForUserStream(Map<String, String> params, RealmModel realm) {
+        List<UserModel> value = this.searchForUser(params, realm);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Search for user by parameter.    Valid parameters are:
@@ -293,9 +297,7 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #searchForUserStream(Map, RealmModel, int, int) searchForUserStream} instead.
      */
     @Deprecated
-    default List<UserModel> searchForUser(Map<String, String> params, RealmModel realm, int firstResult, int maxResults) {
+    List<UserModel> searchForUser(Map<String, String> params, RealmModel realm, int firstResult, int maxResults);
-        return this.searchForUserStream(params, realm, firstResult, maxResults).collect(Collectors.toList());
-    }
 
     /**
      * Searches for user by parameter. If possible, implementations should treat the parameter values as partial match patterns
@@ -313,9 +315,12 @@ public interface UserQueryProvider {
      * @param realm a reference to the realm.
      * @param firstResult first result to return. Ignored if negative.
      * @param maxResults maximum number of results to return. Ignored if negative.
-     * @return a non-null {@code Stream} of users that match the search criteria.
+     * @return a non-null {@link Stream} of users that match the search criteria.
      */
-    Stream<UserModel> searchForUserStream(Map<String, String> params, RealmModel realm, int firstResult, int maxResults);
+    default Stream<UserModel> searchForUserStream(Map<String, String> params, RealmModel realm, int firstResult, int maxResults) {
+        List<UserModel> value = this.searchForUser(params, realm, firstResult, maxResults);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Get users that belong to a specific group. Implementations do not have to search in UserFederatedStorageProvider
@@ -329,9 +334,7 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #getGroupMembersStream(RealmModel, GroupModel) getGroupMembersStream} instead.
      */
     @Deprecated
-    default List<UserModel> getGroupMembers(RealmModel realm, GroupModel group) {
+    List<UserModel> getGroupMembers(RealmModel realm, GroupModel group);
-        return this.getGroupMembersStream(realm, group).collect(Collectors.toList());
-    }
 
     /**
      * Obtains users that belong to a specific group. Implementations do not have to search in {@code UserFederatedStorageProvider}
@@ -341,9 +344,12 @@ public interface UserQueryProvider {
      *
      * @param realm a reference to the realm.
      * @param group a reference to the group.
-     * @return a non-null {@code Stream} of users that belong to the group.
+     * @return a non-null {@link Stream} of users that belong to the group.
      */
-    Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group);
+    default Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group) {
+        List<UserModel> value = this.getGroupMembers(realm, group);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Get users that belong to a specific group.  Implementations do not have to search in UserFederatedStorageProvider
@@ -359,9 +365,7 @@ public interface UserQueryProvider {
      * @deprecated Use {@link #getGroupMembersStream(RealmModel, GroupModel, int, int) getGroupMembersStream} instead.
      */
     @Deprecated
-    default List<UserModel> getGroupMembers(RealmModel realm, GroupModel group, int firstResult, int maxResults) {
+    List<UserModel> getGroupMembers(RealmModel realm, GroupModel group, int firstResult, int maxResults);
-        return this.getGroupMembersStream(realm, group, firstResult, maxResults).collect(Collectors.toList());
-    }
 
     /**
      * Obtains users that belong to a specific group.  Implementations do not have to search in {@code UserFederatedStorageProvider}
@@ -373,9 +377,12 @@ public interface UserQueryProvider {
      * @param group a reference to the group.
      * @param firstResult first result to return. Ignored if negative.
      * @param maxResults maximum number of results to return. Ignored if negative.
-     * @return a non-null {@code Stream} of users that belong to the group.
+     * @return a non-null {@link Stream} of users that belong to the group.
      */
-    Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group, int firstResult, int maxResults);
+    default Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group, int firstResult, int maxResults) {
+        List<UserModel> value = this.getGroupMembers(realm, group, firstResult, maxResults);
+        return value != null ? value.stream() : Stream.empty();
+    }
 
     /**
      * Get users that belong to a specific role.
@@ -395,7 +402,7 @@ public interface UserQueryProvider {
      *
      * @param realm a reference to the realm.
      * @param role a reference to the role.
-     * @return a non-null {@code Stream} of users that have the specified role.
+     * @return a non-null {@link Stream} of users that have the specified role.
      */
     default Stream<UserModel> getRoleMembersStream(RealmModel realm, RoleModel role) {
         return Stream.empty();
@@ -422,7 +429,7 @@ public interface UserQueryProvider {
      * @param role a reference to the role.
      * @param firstResult first result to return. Ignored if negative.
      * @param maxResults maximum number of results to return. Ignored if negative.
-     * @return a non-null {@code Stream} of users that have the specified role.
+     * @return a non-null {@link Stream} of users that have the specified role.
      */
     default Stream<UserModel> getRoleMembersStream(RealmModel realm, RoleModel role, int firstResult, int maxResults) {
         return Stream.empty();
@@ -443,9 +450,7 @@ public interface UserQueryProvider {
      * instead.
      */
     @Deprecated
-    default List<UserModel> searchForUserByUserAttribute(String attrName, String attrValue, RealmModel realm) {
+    List<UserModel> searchForUserByUserAttribute(String attrName, String attrValue, RealmModel realm);
-        return this.searchForUserByUserAttributeStream(attrName, attrValue, realm).collect(Collectors.toList());
-    }
 
     /**
      * Searches for users that have a specific attribute with a specific value. Implementations do not have to search in
@@ -456,7 +461,91 @@ public interface UserQueryProvider {
      * @param attrName the attribute name.
      * @param attrValue the attribute value.
      * @param realm a reference to the realm.
-     * @return a non-null {@code Stream} of users that match the search criteria.
+     * @return a non-null {@link Stream} of users that match the search criteria.
      */
-    Stream<UserModel> searchForUserByUserAttributeStream(String attrName, String attrValue, RealmModel realm);
+    default Stream<UserModel> searchForUserByUserAttributeStream(String attrName, String attrValue, RealmModel realm) {
+        List<UserModel> value = this.searchForUserByUserAttribute(attrName, attrValue, realm);
+        return value != null ? value.stream() : Stream.empty();
+    }
+
+    /**
+     * The {@link Streams} interface makes all collection-based methods in {@link UserQueryProvider} default by
+     * providing implementations that delegate to the {@link Stream}-based variants instead of the other way around.
+     * <p/>
+     * It allows for implementations to focus on the {@link Stream}-based approach for processing sets of data and benefit
+     * from the potential memory and performance optimizations of that approach.
+     */
+    interface Streams extends UserQueryProvider {
+        @Override
+        default List<UserModel> getUsers(RealmModel realm) {
+            return this.getUsersStream(realm).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> getUsersStream(RealmModel realm);
+
+        @Override
+        default List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults) {
+            return this.getUsersStream(realm, firstResult, maxResults).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults);
+
+        @Override
+        default List<UserModel> searchForUser(String search, RealmModel realm) {
+            return this.searchForUserStream(search, realm).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> searchForUserStream(String search, RealmModel realm);
+
+        @Override
+        default List<UserModel> searchForUser(String search, RealmModel realm, int firstResult, int maxResults) {
+            return this.searchForUserStream(search, realm, firstResult, maxResults).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> searchForUserStream(String search, RealmModel realm, int firstResult, int maxResults);
+
+        @Override
+        default List<UserModel> searchForUser(Map<String, String> params, RealmModel realm) {
+            return this.searchForUserStream(params, realm).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> searchForUserStream(Map<String, String> params, RealmModel realm);
+
+        @Override
+        default List<UserModel> searchForUser(Map<String, String> params, RealmModel realm, int firstResult, int maxResults) {
+            return this.searchForUserStream(params, realm, firstResult, maxResults).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> searchForUserStream(Map<String, String> params, RealmModel realm, int firstResult, int maxResults);
+
+        @Override
+        default List<UserModel> getGroupMembers(RealmModel realm, GroupModel group) {
+            return this.getGroupMembersStream(realm, group).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group);
+
+        @Override
+        default List<UserModel> getGroupMembers(RealmModel realm, GroupModel group, int firstResult, int maxResults) {
+            return this.getGroupMembersStream(realm, group, firstResult, maxResults).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group, int firstResult, int maxResults);
+
+        @Override
+        default List<UserModel> searchForUserByUserAttribute(String attrName, String attrValue, RealmModel realm) {
+            return this.searchForUserByUserAttributeStream(attrName, attrValue, realm).collect(Collectors.toList());
+        }
+
+        @Override
+        Stream<UserModel> searchForUserByUserAttributeStream(String attrName, String attrValue, RealmModel realm);
+    }
 }

services/src/main/java/org/keycloak/storage/UserStorageManager.java

@@ -17,7 +17,6 @@
 
 package org.keycloak.storage;
 
-import com.google.common.collect.Streams;
 import org.jboss.logging.Logger;
 import org.keycloak.component.ComponentFactory;
 import org.keycloak.component.ComponentModel;
@@ -27,7 +26,6 @@ import org.keycloak.models.FederatedIdentityModel;
 import org.keycloak.models.GroupModel;
 import org.keycloak.models.IdentityProviderModel;
 import org.keycloak.models.KeycloakSession;
-import org.keycloak.models.KeycloakSessionTask;
 import org.keycloak.models.ModelException;
 import org.keycloak.models.ProtocolMapperModel;
 import org.keycloak.models.RealmModel;
@@ -65,7 +63,8 @@ import static org.keycloak.models.utils.KeycloakModelUtils.runJobInTransaction;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class UserStorageManager extends AbstractStorageManager<UserStorageProvider, UserStorageProviderModel> implements UserProvider, OnUserCache, OnCreateComponent, OnUpdateComponent {
+public class UserStorageManager extends AbstractStorageManager<UserStorageProvider, UserStorageProviderModel>
+        implements UserProvider.Streams, OnUserCache, OnCreateComponent, OnUpdateComponent {
 
     private static final Logger logger = Logger.getLogger(UserStorageManager.class);
 
@@ -605,7 +604,7 @@ public class UserStorageManager extends AbstractStorageManager<UserStorageProvid
         Stream<FederatedIdentityModel> stream = StorageId.isLocalStorage(user) ?
                 localStorage().getFederatedIdentitiesStream(user, realm) : Stream.empty();
         if (getFederatedStorage() != null)
-            stream = Streams.concat(stream, getFederatedStorage().getFederatedIdentitiesStream(user.getId(), realm));
+            stream = Stream.concat(stream, getFederatedStorage().getFederatedIdentitiesStream(user.getId(), realm));
         return stream.distinct();
     }
 

testsuite/integration-arquillian/servers/auth-server/services/testsuite-providers/src/main/java/org/keycloak/testsuite/federation/BackwardsCompatibilityUserStorage.java

@@ -57,7 +57,7 @@ import org.keycloak.storage.user.UserRegistrationProvider;
  * @author <a href="mailto:mposolda@redhat.com">Marek Posolda</a>
  */
 public class BackwardsCompatibilityUserStorage implements UserLookupProvider, UserStorageProvider, UserRegistrationProvider,
-        CredentialInputUpdater, CredentialInputValidator, UserQueryProvider {
+        CredentialInputUpdater, CredentialInputValidator, UserQueryProvider.Streams {
 
     private static final Logger log = Logger.getLogger(BackwardsCompatibilityUserStorage.class);
 
@@ -82,7 +82,7 @@ public class BackwardsCompatibilityUserStorage implements UserLookupProvider, Us
     }
 
     private UserModel createUser(RealmModel realm, String username) {
-        return new AbstractUserAdapterFederatedStorage(session, realm,  model) {
+        return new AbstractUserAdapterFederatedStorage.Streams(session, realm,  model) {
             @Override
             public String getUsername() {
                 return username;

testsuite/integration-arquillian/servers/auth-server/services/testsuite-providers/src/main/java/org/keycloak/testsuite/federation/FailableHardcodedStorageProvider.java

@@ -43,7 +43,8 @@ import java.util.stream.Stream;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class FailableHardcodedStorageProvider implements UserStorageProvider, UserLookupProvider, UserQueryProvider, ImportedUserValidation, CredentialInputUpdater, CredentialInputValidator {
+public class FailableHardcodedStorageProvider implements UserStorageProvider, UserLookupProvider, UserQueryProvider.Streams,
+        ImportedUserValidation, CredentialInputUpdater, CredentialInputValidator {
 
     public static String username = "billb";
     public static String password = "password";

testsuite/integration-arquillian/servers/auth-server/services/testsuite-providers/src/main/java/org/keycloak/testsuite/federation/HardcodedGroupStorageProvider.java

@@ -68,7 +68,7 @@ public class HardcodedGroupStorageProvider implements GroupStorageProvider {
     }
 
 
-    public class HardcodedGroupAdapter implements GroupModel {
+    public class HardcodedGroupAdapter implements GroupModel.Streams {
 
         private final RealmModel realm;
         private StorageId storageId;

testsuite/integration-arquillian/servers/auth-server/services/testsuite-providers/src/main/java/org/keycloak/testsuite/federation/PassThroughFederatedUserStorageProvider.java

@@ -154,7 +154,7 @@ public class PassThroughFederatedUserStorageProvider implements
     }
 
     private UserModel getUserModel(final RealmModel realm) {
-        return new AbstractUserAdapterFederatedStorage(session, realm, component) {
+        return new AbstractUserAdapterFederatedStorage.Streams(session, realm, component) {
             @Override
             public String getUsername() {
                 return PASSTHROUGH_USERNAME;

testsuite/integration-arquillian/servers/auth-server/services/testsuite-providers/src/main/java/org/keycloak/testsuite/federation/UserMapStorage.java

@@ -54,8 +54,8 @@ import static org.keycloak.storage.UserStorageProviderModel.IMPORT_ENABLED;
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
  * @version $Revision: 1 $
  */
-public class UserMapStorage implements UserLookupProvider, UserStorageProvider, UserRegistrationProvider, CredentialInputUpdater, CredentialInputValidator,
+public class UserMapStorage implements UserLookupProvider, UserStorageProvider, UserRegistrationProvider, CredentialInputUpdater,
-  UserGroupMembershipFederatedStorage, UserQueryProvider, ImportedUserValidation {
+        CredentialInputValidator, UserGroupMembershipFederatedStorage.Streams, UserQueryProvider.Streams, ImportedUserValidation {
 
     private static final Logger log = Logger.getLogger(UserMapStorage.class);
     
@@ -113,7 +113,7 @@ public class UserMapStorage implements UserLookupProvider, UserStorageProvider,
             user.setEnabled(true);
             user.setFederationLink(model.getId());
         } else {
-            user = new AbstractUserAdapterFederatedStorage(session, realm, model) {
+            user = new AbstractUserAdapterFederatedStorage.Streams(session, realm, model) {
                 @Override
                 public String getUsername() {
                     return username;

testsuite/integration-arquillian/servers/auth-server/services/testsuite-providers/src/main/java/org/keycloak/testsuite/federation/UserPropertyFileStorage.java

@@ -33,11 +33,13 @@ import org.keycloak.storage.adapter.AbstractUserAdapterFederatedStorage;
 import org.keycloak.storage.user.UserLookupProvider;
 import org.keycloak.storage.user.UserQueryProvider;
 
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Properties;
 import java.util.function.Predicate;
-import java.util.stream.Stream;
 
 /**
  * @author <a href="mailto:bill@burkecentral.com">Bill Burke</a>
@@ -69,7 +71,7 @@ public class UserPropertyFileStorage implements UserLookupProvider, UserStorageP
 
     private UserModel createUser(RealmModel realm, String username) {
         if (federatedStorageEnabled) {
-            return new AbstractUserAdapterFederatedStorage(session, realm,  model) {
+            return new AbstractUserAdapterFederatedStorage.Streams(session, realm,  model) {
                 @Override
                 public String getUsername() {
                     return username;
@@ -81,7 +83,7 @@ public class UserPropertyFileStorage implements UserLookupProvider, UserStorageP
                 }
             };
         } else {
-            return new AbstractUserAdapter(session, realm, model) {
+            return new AbstractUserAdapter.Streams(session, realm, model) {
                 @Override
                 public String getUsername() {
                     return username;
@@ -90,7 +92,6 @@ public class UserPropertyFileStorage implements UserLookupProvider, UserStorageP
         }
     }
 
-    @Override
     public UserModel getUserByUsername(String username, RealmModel realm) {
         if (!userPasswords.containsKey(username)) return null;
 
@@ -144,59 +145,67 @@ public class UserPropertyFileStorage implements UserLookupProvider, UserStorageP
     }
 
     @Override
-    public Stream<UserModel> getUsersStream(RealmModel realm) {
+    public List<UserModel> getUsers(RealmModel realm) {
-        return userPasswords.keySet().stream().map(obj -> createUser(realm, (String) obj));
+        List<UserModel> users = new LinkedList<>();
+        for (Object username : userPasswords.keySet()) {
+            users.add(createUser(realm, (String)username));
+        }
+        return users;
     }
 
     @Override
-    public Stream<UserModel> searchForUserStream(Map<String, String> attributes, RealmModel realm) {
+    public List<UserModel> searchForUser(Map<String, String> attributes, RealmModel realm) {
-        return searchForUserStream(attributes, realm, 0, Integer.MAX_VALUE - 1);
+        return searchForUser(attributes, realm, 0, Integer.MAX_VALUE - 1);
     }
 
     @Override
-    public Stream<UserModel> getUsersStream(RealmModel realm, int firstResult, int maxResults) {
+    public List<UserModel> getUsers(RealmModel realm, int firstResult, int maxResults) {
-        Stream<Object> stream = userPasswords.keySet().stream();
+        if (maxResults == 0) return Collections.EMPTY_LIST;
-        if (firstResult > 0)
+        List<UserModel> users = new LinkedList<>();
-            stream = stream.skip(firstResult);
+        int count = 0;
-        if (maxResults >= 0)
+        for (Object un : userPasswords.keySet()) {
-            stream = stream.limit(maxResults);
+            if (count++ < firstResult) continue;
-        return stream.map(obj -> createUser(realm, (String) obj));
+            String username = (String)un;
+            users.add(createUser(realm, username));
+            if (users.size() + 1 > maxResults) break;
+        }
+        return users;
     }
 
     @Override
-    public Stream<UserModel> searchForUserStream(String search, RealmModel realm, int firstResult, int maxResults) {
+    public List<UserModel> searchForUser(String search, RealmModel realm, int firstResult, int maxResults) {
-        return searchForUserStream(search, realm, firstResult, maxResults, username -> username.contains(search));
+        return searchForUser(search, realm, firstResult, maxResults, username -> username.contains(search));
     }
 
     @Override
-    public Stream<UserModel> searchForUserStream(Map<String, String> attributes, RealmModel realm, int firstResult, int maxResults) {
+    public List<UserModel> searchForUser(Map<String, String> attributes, RealmModel realm, int firstResult, int maxResults) {
         String search = Optional.ofNullable(attributes.get(UserModel.USERNAME))
                 .orElseGet(()-> attributes.get(UserModel.SEARCH));
-        if (search == null) return Stream.empty();
+        if (search == null) return Collections.EMPTY_LIST;
         Predicate<String> p = Boolean.valueOf(attributes.getOrDefault(UserModel.EXACT, Boolean.FALSE.toString()))
-            ? username -> username.equals(search)
+                ? username -> username.equals(search)
-            : username -> username.contains(search);
+                : username -> username.contains(search);
-        return searchForUserStream(search, realm, firstResult, maxResults, p);
+        return searchForUser(search, realm, firstResult, maxResults, p);
     }
 
     @Override
-    public Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group, int firstResult, int maxResults) {
+    public List<UserModel> getGroupMembers(RealmModel realm, GroupModel group, int firstResult, int maxResults) {
-        return Stream.empty();
+        return Collections.EMPTY_LIST;
     }
 
     @Override
-    public Stream<UserModel> getGroupMembersStream(RealmModel realm, GroupModel group) {
+    public List<UserModel> getGroupMembers(RealmModel realm, GroupModel group) {
-        return Stream.empty();
+        return Collections.EMPTY_LIST;
     }
 
     @Override
-    public Stream<UserModel> searchForUserStream(String search, RealmModel realm) {
+    public List<UserModel> searchForUser(String search, RealmModel realm) {
-        return searchForUserStream(search, realm, 0, Integer.MAX_VALUE - 1);
+        return searchForUser(search, realm, 0, Integer.MAX_VALUE - 1);
     }
 
     @Override
-    public Stream<UserModel> searchForUserByUserAttributeStream(String attrName, String attrValue, RealmModel realm) {
+    public List<UserModel> searchForUserByUserAttribute(String attrName, String attrValue, RealmModel realm) {
-        return Stream.empty();
+        return Collections.EMPTY_LIST;
     }
 
     @Override
@@ -204,8 +213,20 @@ public class UserPropertyFileStorage implements UserLookupProvider, UserStorageP
 
     }
 
-    private Stream<UserModel> searchForUserStream(String search, RealmModel realm, int firstResult, int maxResults, Predicate<String> matcher) {
+    private List<UserModel> searchForUser(String search, RealmModel realm, int firstResult, int maxResults, Predicate<String> matcher) {
-        return userPasswords.keySet().stream().filter(obj -> matcher.test((String) obj)).skip(firstResult < 0 ? 0 : firstResult)
+        if (maxResults == 0) return Collections.EMPTY_LIST;
-                .limit(maxResults < 0 ? 0 : maxResults).map(obj -> createUser(realm, (String) obj));
+        List<UserModel> users = new LinkedList<>();
+        int count = 0;
+        for (Object un : userPasswords.keySet()) {
+            String username = (String)un;
+            if (matcher.test(username)) {
+                if (count++ < firstResult) {
+                    continue;
+                }
+                users.add(createUser(realm, username));
+                if (users.size() + 1 > maxResults) break;
+            }
+        }
+        return users;
     }
 }