Correct pagination

scm-core/src/main/java/sonia/scm/Manager.java

@@ -35,8 +35,9 @@ package sonia.scm;
 
 //~--- JDK imports ------------------------------------------------------------
 
-import java.io.IOException;
+import sonia.scm.util.Util;
 
+import java.io.IOException;
 import java.util.Collection;
 import java.util.Comparator;
 
@@ -61,7 +62,7 @@ public interface Manager<T extends ModelObject, E extends Exception>
    * @throws E
    * @throws IOException
    */
-  public void refresh(T object) throws E, IOException;
+  void refresh(T object) throws E, IOException;
 
   //~--- get methods ----------------------------------------------------------
 
@@ -73,7 +74,7 @@ public interface Manager<T extends ModelObject, E extends Exception>
    *
    * @return object with the given id
    */
-  public T get(String id);
+  T get(String id);
 
   /**
    * Returns a {@link java.util.Collection} of all objects in the store.
@@ -81,7 +82,7 @@ public interface Manager<T extends ModelObject, E extends Exception>
    *
    * @return all object in the store
    */
-  public Collection<T> getAll();
+  Collection<T> getAll();
 
   /**
    * Returns all object of the store sorted by the given {@link java.util.Comparator}
@@ -91,7 +92,7 @@ public interface Manager<T extends ModelObject, E extends Exception>
    * @since 1.4
    * @return all object of the store sorted by the given {@link java.util.Comparator}
    */
-  public Collection<T> getAll(Comparator<T> comparator);
+  Collection<T> getAll(Comparator<T> comparator);
 
   /**
    * Returns objects from the store which are starts at the given start
@@ -105,7 +106,7 @@ public interface Manager<T extends ModelObject, E extends Exception>
    * @return objects from the store which are starts at the given 
    *         start parameter
    */
-  public Collection<T> getAll(int start, int limit);
+  Collection<T> getAll(int start, int limit);
 
   /**
    * Returns objects from the store which are starts at the given start
@@ -121,5 +122,26 @@ public interface Manager<T extends ModelObject, E extends Exception>
    * @return objects from the store which are starts at the given 
    *         start parameter
    */
-  public Collection<T> getAll(Comparator<T> comparator, int start, int limit);
+  Collection<T> getAll(Comparator<T> comparator, int start, int limit);
+
+  /**
+   * Returns objects from the store divided into pages with the given page
+   * size for the given page number (zero based) and sorted by the given
+   * {@link java.util.Comparator}.
+   *
+   * @param comparator to sort the returned objects
+   * @param pageNumber the number of the page to be returned (zero based)
+   * @param pageSize the size of the pages
+   *
+   * @since 2.0
+   * @return {@link PageResult} with the objects from the store for the requested
+   *         page. If the requested page number exceeds the existing pages, an
+   *         empty page result is returned.
+   */
+  default PageResult<T> getPage(Comparator<T> comparator, int pageNumber, int pageSize) {
+    Collection<T> entities = getAll(comparator, pageNumber * pageSize, pageSize + 1);
+    boolean hasMore = entities.size() > pageSize;
+    return new PageResult<>(Util.createSubCollection(entities, 0, pageSize), hasMore);
+  }
+
 }

scm-core/src/main/java/sonia/scm/PageResult.java

@@ -0,0 +1,23 @@
+package sonia.scm;
+
+import java.util.Collection;
+import java.util.Collections;
+
+public class PageResult<T extends ModelObject> {
+
+  private final Collection<T> entities;
+  private final boolean hasMore;
+
+  public PageResult(Collection<T> entities, boolean hasMore) {
+    this.entities = entities;
+    this.hasMore = hasMore;
+  }
+
+  public Collection<T> getEntities() {
+    return Collections.unmodifiableCollection(entities);
+  }
+
+  public boolean hasMore() {
+    return hasMore;
+  }
+}

scm-webapp/src/main/java/sonia/scm/api/rest/resources/AbstractManagerResource.java

@@ -42,6 +42,7 @@ import org.slf4j.LoggerFactory;
 import sonia.scm.LastModifiedAware;
 import sonia.scm.Manager;
 import sonia.scm.ModelObject;
+import sonia.scm.PageResult;
 import sonia.scm.api.rest.RestExceptionResult;
 import sonia.scm.util.AssertUtil;
 import sonia.scm.util.HttpUtil;
@@ -588,6 +589,19 @@ public abstract class AbstractManagerResource<T extends ModelObject,
     return items;
   }
 
+  protected PageResult<T> fetchPage(String sortby, boolean desc, int pageNumber,
+    int pageSize) {
+    AssertUtil.assertPositive(pageNumber);
+    AssertUtil.assertPositive(pageSize);
+
+    if (Util.isEmpty(sortby)) {
+      // replace with something useful
+      sortby = "id";
+    }
+
+    return manager.getPage(createComparator(sortby, desc), pageNumber, pageSize);
+  }
+
   //~--- get methods ----------------------------------------------------------
 
   /**

scm-webapp/src/main/java/sonia/scm/api/v2/resources/UserCollectionDto.java

@@ -13,11 +13,12 @@ import static de.otto.edison.hal.Links.linkingTo;
 
 public class UserCollectionDto extends HalRepresentation {
   public UserCollectionDto(String baseUrl, NumberedPaging page, List<UserDto> users) {
-    super(linkingTo()
-      .with(page.links(
-        fromTemplate(baseUrl + "{?page,pageSize}"),
-        EnumSet.allOf(PagingRel.class)))
-      .build(),
+    super(
+      linkingTo()
+        .with(page.links(
+          fromTemplate(baseUrl + "{?page,pageSize}"),
+          EnumSet.allOf(PagingRel.class)))
+        .build(),
       embeddedBuilder()
         .with("users", users)
         .build()

scm-webapp/src/main/java/sonia/scm/api/v2/resources/UserCollectionResource.java

@@ -6,6 +6,7 @@ import com.webcohesion.enunciate.metadata.rs.ResponseCode;
 import com.webcohesion.enunciate.metadata.rs.ResponseHeader;
 import com.webcohesion.enunciate.metadata.rs.StatusCodes;
 import com.webcohesion.enunciate.metadata.rs.TypeHint;
+import sonia.scm.PageResult;
 import sonia.scm.api.rest.resources.AbstractManagerResource;
 import sonia.scm.user.User;
 import sonia.scm.user.UserException;
@@ -24,6 +25,7 @@ import static sonia.scm.api.v2.resources.ScmMediaType.USER;
 @Singleton
 @Produces(USER)
 public class UserCollectionResource extends AbstractManagerResource<User, UserException> {
+  public static final int DEFAULT_PAGE_SIZE = 10;
   private final UserDto2UserMapper dtoToUserMapper;
   private final User2UserDtoMapper userToDtoMapper;
 
@@ -53,18 +55,18 @@ public class UserCollectionResource extends AbstractManagerResource<User, UserEx
     @ResponseCode(code = 500, condition = "internal server error")
   })
   public Response getAll(@Context Request request, @Context UriInfo uriInfo, @DefaultValue("0")
-  @QueryParam("page") int page, @DefaultValue("10")
+  @QueryParam("page") int page, @DefaultValue("" + DEFAULT_PAGE_SIZE)
   @QueryParam("pageSize") int pageSize, @QueryParam("sortby") String sortby,
     @DefaultValue("false")
     @QueryParam("desc") boolean desc) {
-    Collection<User> items = fetchItems(sortby, desc, page * pageSize, pageSize);
+    PageResult<User> pageResult = fetchPage(sortby, desc, page, pageSize);
 
     LinkBuilder collectionLinkBuilder = new LinkBuilder(uriInfo, UserV2Resource.class, UserCollectionResource.class);
     String baseUrl = collectionLinkBuilder.method("getUserCollectionResource").parameters().method("create").parameters().href();
 
-    List<UserDto> dtos = items.stream().map(user -> userToDtoMapper.userToUserDto(user, uriInfo)).collect(Collectors.toList());
+    List<UserDto> dtos = pageResult.getEntities().stream().map(user -> userToDtoMapper.userToUserDto(user, uriInfo)).collect(Collectors.toList());
 
-    return Response.ok(new UserCollectionDto(baseUrl, zeroBasedNumberedPaging(page, pageSize, true), dtos)).build();
+    return Response.ok(new UserCollectionDto(baseUrl, zeroBasedNumberedPaging(page, pageSize, pageResult.hasMore()), dtos)).build();
   }
 
   @POST