DATAJPA-677 - Add support for Java 8 Stream in repository finder methods.

Added support for Streaming query results in Hibernate, EclipseLink and OpenJPA by falling back to store specific APIs to execute the query.

Original pull request: #136.

src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -28,6 +28,8 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
 
 import javax.persistence.EntityManager;
 import javax.persistence.PersistenceContext;
@@ -1751,8 +1753,8 @@ public class UserRepositoryTests {
 		assertThat(users.getContent(), hasSize(2));
 		assertThat(users.getContent().get(0), is(thirdUser));
 		assertThat(users.getContent().get(1), is(fourthUser));
-	}
-
+	}
+
 	/**
 	 * @see DATAJPA-629
 	 */
@@ -1816,6 +1818,66 @@ public class UserRepositoryTests {
 		assertThat(users.get(0), is(secondUser));
 	}
 
+	/**
+	 * @see DATAJPA-677
+	 */
+	@Test
+	public void shouldSupportJava8StreamsForRepositoryFinderMethods() {
+
+		flushTestUsers();
+
+		Stream<User> stream = repository.findAllByCustomQueryAndStream();
+
+		final List<User> users = new ArrayList<User>();
+
+		try {
+			stream.forEach(new Consumer<User>() {
+
+				@Override
+				public void accept(User user) {
+
+					// System.out.printf("%s%n", user);
+					users.add(user);
+				}
+
+			});
+		} finally {
+			stream.close();
+		}
+
+		assertThat(users, hasSize(4));
+	}
+
+	/**
+	 * @see DATAJPA-677
+	 */
+	@Test
+	public void shouldSupportJava8StreamsForRepositoryDerivedFinderMethods() {
+
+		flushTestUsers();
+
+		Stream<User> stream = repository.readAllByFirstnameNotNull();
+
+		final List<User> users = new ArrayList<User>();
+
+		try {
+			stream.forEach(new Consumer<User>() {
+
+				@Override
+				public void accept(User user) {
+
+					// System.out.printf("%s%n", user);
+					users.add(user);
+				}
+
+			});
+		} finally {
+			stream.close();
+		}
+
+		assertThat(users, hasSize(4));
+	}
+
 	private Page<User> executeSpecWithSort(Sort sort) {
 
 		flushTestUsers();

src/test/java/org/springframework/data/jpa/repository/sample/UserRepository.java

@@ -19,6 +19,7 @@ import java.util.Collection;
 import java.util.Date;
 import java.util.List;
 import java.util.Set;
+import java.util.stream.Stream;
 
 import javax.persistence.EntityManager;
 import javax.persistence.QueryHint;
@@ -557,4 +558,15 @@ public interface UserRepository extends JpaRepository<User, Integer>, JpaSpecifi
 	 * DATAJPA-606
 	 */
 	List<User> queryByAgeInOrFirstname(Integer[] ages, String firstname);
+
+	/**
+	 * DATAJPA-677
+	 */
+	@Query("select u from User u")
+	Stream<User> findAllByCustomQueryAndStream();
+
+	/**
+	 * DATAJPA-677
+	 */
+	Stream<User> readAllByFirstnameNotNull();
 }