Add documentation for streaming results.

Also us Github issue numbers on tests.

Original pull request #903
See #578, #971

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/query/QueryAnnotationHsqlIntegrationTests.java

@@ -174,7 +174,7 @@ public class QueryAnnotationHsqlIntegrationTests {
 				.containsExactlyInAnyOrder("a", "b");
 	}
 
-	@Test // DATAJDBC-356
+	@Test // GH-578
 	public void executeCustomQueryWithNamedParameterAndReturnTypeIsStream() {
 
 		repository.save(dummyEntity("a"));

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/query/StringBasedJdbcQueryUnitTests.java

@@ -40,7 +40,6 @@ import org.springframework.data.relational.core.mapping.RelationalMappingContext
 import org.springframework.data.repository.Repository;
 import org.springframework.data.repository.core.support.DefaultRepositoryMetadata;
 import org.springframework.data.repository.core.support.PropertiesBasedNamedQueries;
-import org.springframework.data.repository.query.DefaultParameters;
 import org.springframework.jdbc.core.ResultSetExtractor;
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.jdbc.core.namedparam.NamedParameterJdbcOperations;
@@ -57,8 +56,7 @@ import org.springframework.util.ReflectionUtils;
  * @author Mark Paluch
  * @author Dennis Effing
  */
-public class StringBasedJdbcQueryUnitTests {
-
+class StringBasedJdbcQueryUnitTests {
 
 	RowMapper<Object> defaultRowMapper;
 	NamedParameterJdbcOperations operations;
@@ -66,7 +64,7 @@ public class StringBasedJdbcQueryUnitTests {
 	JdbcConverter converter;
 
 	@BeforeEach
-	public void setup() throws NoSuchMethodException {
+	void setup() throws NoSuchMethodException {
 
 		this.defaultRowMapper = mock(RowMapper.class);
 		this.operations = mock(NamedParameterJdbcOperations.class);
@@ -75,17 +73,16 @@ public class StringBasedJdbcQueryUnitTests {
 	}
 
 	@Test // DATAJDBC-165
-	public void emptyQueryThrowsException() {
+	void emptyQueryThrowsException() {
 
 		JdbcQueryMethod queryMethod = createMethod("noAnnotation");
 
 		Assertions.assertThatExceptionOfType(IllegalStateException.class) //
-				.isThrownBy(() -> createQuery(queryMethod)
-						.execute(new Object[] {}));
+				.isThrownBy(() -> createQuery(queryMethod).execute(new Object[] {}));
 	}
 
 	@Test // DATAJDBC-165
-	public void defaultRowMapperIsUsedByDefault() {
+	void defaultRowMapperIsUsedByDefault() {
 
 		JdbcQueryMethod queryMethod = createMethod("findAll");
 		StringBasedJdbcQuery query = createQuery(queryMethod);
@@ -94,7 +91,7 @@ public class StringBasedJdbcQueryUnitTests {
 	}
 
 	@Test // DATAJDBC-165, DATAJDBC-318
-	public void customRowMapperIsUsedWhenSpecified() {
+	void customRowMapperIsUsedWhenSpecified() {
 
 		JdbcQueryMethod queryMethod = createMethod("findAllWithCustomRowMapper");
 		StringBasedJdbcQuery query = createQuery(queryMethod);
@@ -103,7 +100,7 @@ public class StringBasedJdbcQueryUnitTests {
 	}
 
 	@Test // DATAJDBC-290
-	public void customResultSetExtractorIsUsedWhenSpecified() {
+	void customResultSetExtractorIsUsedWhenSpecified() {
 
 		JdbcQueryMethod queryMethod = createMethod("findAllWithCustomResultSetExtractor");
 		StringBasedJdbcQuery query = createQuery(queryMethod);
@@ -117,7 +114,7 @@ public class StringBasedJdbcQueryUnitTests {
 	}
 
 	@Test // DATAJDBC-290
-	public void customResultSetExtractorAndRowMapperGetCombined() {
+	void customResultSetExtractorAndRowMapperGetCombined() {
 
 		JdbcQueryMethod queryMethod = createMethod("findAllWithCustomRowMapperAndResultSetExtractor");
 		StringBasedJdbcQuery query = createQuery(queryMethod);
@@ -131,8 +128,9 @@ public class StringBasedJdbcQueryUnitTests {
 						"RowMapper is not expected to be custom");
 	}
 
-	@Test // DATAJDBC-356
-	public void streamQueryCallsQueryForStreamOnOperations() {
+	@Test // GH-578
+	void streamQueryCallsQueryForStreamOnOperations() {
+
 		JdbcQueryMethod queryMethod = createMethod("findAllWithStreamReturnType");
 		StringBasedJdbcQuery query = createQuery(queryMethod);
 
@@ -141,20 +139,21 @@ public class StringBasedJdbcQueryUnitTests {
 		verify(operations).queryForStream(eq("some sql statement"), any(SqlParameterSource.class), any(RowMapper.class));
 	}
 
-	@Test // DATAJDBC-356
+	@Test // GH-578
 	void streamQueryFallsBackToCollectionQueryWhenCustomResultSetExtractorIsSpecified() {
+
 		JdbcQueryMethod queryMethod = createMethod("findAllWithStreamReturnTypeAndResultSetExtractor");
 		StringBasedJdbcQuery query = createQuery(queryMethod);
 
 		query.execute(new Object[] {});
 
-		ArgumentCaptor<ResultSetExtractor> captor = ArgumentCaptor.forClass(ResultSetExtractor.class);
+		ArgumentCaptor<ResultSetExtractor<?>> captor = ArgumentCaptor.forClass(ResultSetExtractor.class);
 		verify(operations).query(eq("some sql statement"), any(SqlParameterSource.class), captor.capture());
 		assertThat(captor.getValue()).isInstanceOf(CustomResultSetExtractor.class);
 	}
 
 	@Test // GH-774
-	public void sliceQueryNotSupported() {
+	void sliceQueryNotSupported() {
 
 		JdbcQueryMethod queryMethod = createMethod("sliceAll", Pageable.class);
 
@@ -164,7 +163,7 @@ public class StringBasedJdbcQueryUnitTests {
 	}
 
 	@Test // GH-774
-	public void pageQueryNotSupported() {
+	void pageQueryNotSupported() {
 
 		JdbcQueryMethod queryMethod = createMethod("pageAll", Pageable.class);
 

src/main/asciidoc/jdbc.adoc

@@ -466,6 +466,8 @@ interface PersonRepository extends PagingAndSortingRepository<Person, String> {
 
   @Query("SELECT * FROM person WHERE lastname = :lastname")
   List<Person> findByLastname(String lastname);                                     <7>
+  @Query("SELECT * FROM person WHERE lastname = :lastname")
+  Stream<Person> streamByLastname(String lastname);                                     <8>
 }
 ----
 <1> The method shows a query for all people with the given `lastname`.
@@ -478,6 +480,7 @@ Thus, the method name results in a query expression of `SELECT … FROM person W
 It completes with `IncorrectResultSizeDataAccessException` on non-unique results.
 <6> In contrast to <3>, the first entity is always emitted even if the query yields more result documents.
 <7> The `findByLastname` method shows a query for all people with the given last name.
+<8> The `streamByLastname` method returns a `Stream` which makes values possible as soon as they are returned from the database.
 ====
 
 The following table shows the keywords that are supported for query methods:
@@ -622,6 +625,17 @@ Named queries are expected to be provided in the property file `META-INF/jdbc-na
 
 The location of that file may be changed by setting a value to `@EnableJdbcRepositories.namedQueriesLocation`.
 
+[[jdbc.query-methods.at-query.streaming-results]]
+==== Streaming Results
+
+When you specify `Stream` as the return type of a query method Spring Data JDBC will return elements as soon as they become available.
+When dealing with large amounts of data this is suitable for reducing latency and memory requirements.
+
+The stream contains an open connection to the database.
+To avoid memory leaks that connection needs to be closed eventually by closing the stream.
+The recommended way to do that is a try-with-resource clause.
+It also means once the connection to the database is closed, the stream cannot obtain further elements and will likely throw an exception.
+
 [[jdbc.query-methods.at-query.custom-rowmapper]]
 ==== Custom `RowMapper`
 

src/main/asciidoc/new-features.adoc

@@ -3,8 +3,15 @@
 
 This section covers the significant changes for each version.
 
+[[new-features.2-3-0]]
+==  What's New in Spring Data JDBC 2.3
+
+* Support for <<jdbc.query-methods.at-query.streaming-results, streaming results>>.
+* Support for specifying projection types as return type or using generics and providing a Class parameter to query methods.
+
 [[new-features.2-2-0]]
-== `Page` and `Slice` support for <<jdbc.query-methods,derived queries>>.
+==  What's New in Spring Data JDBC 2.2
+* `Page` and `Slice` support for <<jdbc.query-methods,derived queries>>.
 
 [[new-features.2-1-0]]
 == What's New in Spring Data JDBC 2.1