Avoid superfluous creation of RowMappers.

For modifying queries RowMappers get now longer created.
Improved documentation for `@Query` annotation.

Original pull request #1423

Author: mipo256

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/AbstractJdbcQuery.java

@@ -82,10 +82,6 @@ public JdbcQueryMethod getQueryMethod() {
 	protected JdbcQueryExecution<?> getQueryExecution(JdbcQueryMethod queryMethod,
 			@Nullable ResultSetExtractor<?> extractor, RowMapper<?> rowMapper) {
 
-		if (queryMethod.isModifyingQuery()) {
-			return createModifyingQueryExecutor();
-		}
-
 		if (queryMethod.isCollectionQuery()) {
 			return extractor != null ? getQueryExecution(extractor) : collectionQuery(rowMapper);
 		}
@@ -97,7 +93,7 @@ protected JdbcQueryExecution<?> getQueryExecution(JdbcQueryMethod queryMethod,
 		return extractor != null ? getQueryExecution(extractor) : singleObjectQuery(rowMapper);
 	}
 
-	private JdbcQueryExecution<Object> createModifyingQueryExecutor() {
+	protected JdbcQueryExecution<Object> createModifyingQueryExecutor() {
 
 		return (query, parameters) -> {
 

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/PartTreeJdbcQuery.java

@@ -43,6 +43,7 @@
 import org.springframework.jdbc.core.RowMapper;
 import org.springframework.jdbc.core.namedparam.NamedParameterJdbcOperations;
 import org.springframework.jdbc.core.namedparam.SqlParameterSource;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -144,9 +145,7 @@ private JdbcQueryExecution<?> getQueryExecution(ResultProcessor processor,
 					resultProcessingConverter);
 		}
 
-		JdbcQueryExecution<?> queryExecution = getQueryMethod().isPageQuery() || getQueryMethod().isSliceQuery()
-				? collectionQuery(rowMapper)
-				: getQueryExecution(getQueryMethod(), extractor, rowMapper);
+		JdbcQueryExecution<?> queryExecution = getJdbcQueryExecution(extractor, rowMapper);
 
 		if (getQueryMethod().isSliceQuery()) {
 			return new SliceQueryExecution<>((JdbcQueryExecution<Collection<Object>>) queryExecution, accessor.getPageable());
@@ -173,6 +172,18 @@ private JdbcQueryExecution<?> getQueryExecution(ResultProcessor processor,
 		return queryExecution;
 	}
 
+	private JdbcQueryExecution<?> getJdbcQueryExecution(@Nullable ResultSetExtractor<Boolean> extractor, RowMapper<Object> rowMapper) {
+		if (getQueryMethod().isPageQuery() || getQueryMethod().isSliceQuery()) {
+			return collectionQuery(rowMapper);
+		} else {
+			if (getQueryMethod().isModifyingQuery()) {
+				return createModifyingQueryExecutor();
+			} else {
+				return getQueryExecution(getQueryMethod(), extractor, rowMapper);
+			}
+		}
+	}
+
 	protected ParametrizedQuery createQuery(RelationalParametersParameterAccessor accessor, ReturnedType returnedType) {
 
 		RelationalEntityMetadata<?> entityMetadata = getQueryMethod().getEntityInformation();

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/Query.java

@@ -29,6 +29,18 @@
  * Annotation to provide SQL statements that will get used for executing the method. The SQL statement may contain named
  * parameters as supported by {@link org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate}. Those
  * parameters will get bound to the arguments of the annotated method.
+ * <p>
+ * You can also specify the way to extract data from {@link java.sql.ResultSet}. There are 4 attribute of this
+ * annotation you can set to do that:
+ * <p>
+ * 1. {@link #resultSetExtractorRef()}
+ * 2. {@link #resultSetExtractorClass()}
+ * 3. {@link #rowMapperRef()}
+ * 4. {@link #rowMapperClass()}
+ *
+ * The annotation attributes above are listed in their preference order, that is - the {@link #resultSetExtractorRef()},
+ * has the highest privilege and, will suppress any other 3 attribute from above, and consequently {@link #rowMapperClass()}
+ * has the lowest privilege and will be used if any of three above are not specified.
  *
  * @author Jens Schauder
  * @author Moises Cisneros
@@ -52,28 +64,23 @@
 	String name() default "";
 
 	/**
-	 * Optional {@link RowMapper} to use to convert the result of the query to domain class instances. Cannot be used
-	 * along with {@link #resultSetExtractorClass()} only one of the two can be set.
+	 * Optional {@link RowMapper} to use to convert the result of the query to domain class instances.
 	 */
 	Class<? extends RowMapper> rowMapperClass() default RowMapper.class;
 
 	/**
-	 * Optional name of a bean of type {@link RowMapper} to use to convert the result of the query to domain class instances. Cannot be used
-	 * along with {@link #resultSetExtractorClass()} only one of the two can be set.
-	 *
+	 * Optional name of a bean of type {@link RowMapper} to use to convert the result of the query to domain class instances.
 	 * @since 2.1
 	 */
 	String rowMapperRef() default "";
 
 	/**
-	 * Optional {@link ResultSetExtractor} to use to convert the result of the query to domain class instances. Cannot be
-	 * used along with {@link #rowMapperClass()} only one of the two can be set.
+	 * Optional {@link ResultSetExtractor} to use to convert the result of the query to domain class instances.
 	 */
 	Class<? extends ResultSetExtractor> resultSetExtractorClass() default ResultSetExtractor.class;
 
 	/**
-	 * Optional name of a bean of type {@link ResultSetExtractor} to use to convert the result of the query to domain class instances. Cannot be
-	 * used along with {@link #rowMapperClass()} only one of the two can be set.
+	 * Optional name of a bean of type {@link ResultSetExtractor} to use to convert the result of the query to domain class instances.
 	 *
 	 * @since 2.1
 	 */

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/StringBasedJdbcQuery.java

@@ -128,13 +128,7 @@ public Object execute(Object[] objects) {
 		ResultProcessingConverter converter = new ResultProcessingConverter(processor, this.converter.getMappingContext(),
 				this.converter.getEntityInstantiators());
 
-		RowMapper<Object> rowMapper = determineRowMapper(rowMapperFactory.create(resolveTypeToRead(processor)), converter,
-				accessor.findDynamicProjection() != null);
-
-		JdbcQueryExecution<?> queryExecution = getQueryExecution(//
-				queryMethod, //
-				determineResultSetExtractor(rowMapper), //
-				rowMapper);
+		JdbcQueryExecution<?> queryExecution = createJdbcQueryExecution(accessor, processor, converter);
 
 		MapSqlParameterSource parameterMap = this.bindParameters(accessor);
 
@@ -147,6 +141,21 @@ public Object execute(Object[] objects) {
 		return queryExecution.execute(processSpelExpressions(objects, parameterMap, query), parameterMap);
 	}
 
+	private JdbcQueryExecution<?> createJdbcQueryExecution(RelationalParameterAccessor accessor, ResultProcessor processor, ResultProcessingConverter converter) {
+		JdbcQueryExecution<?> queryExecution;
+
+		if (queryMethod.isModifyingQuery()) {
+			queryExecution = createModifyingQueryExecutor();
+		} else {
+
+			RowMapper<Object> rowMapper = determineRowMapper(rowMapperFactory.create(resolveTypeToRead(processor)), converter,
+					accessor.findDynamicProjection() != null);
+
+			queryExecution = getQueryExecution(queryMethod, determineResultSetExtractor(rowMapper), rowMapper);
+		}
+		return queryExecution;
+	}
+
 	private String processSpelExpressions(Object[] objects, MapSqlParameterSource parameterMap, String query) {
 
 		SpelQueryContext.EvaluatingSpelQueryContext queryContext = SpelQueryContext