#664 Annotate mapper implementations with @Singleton when using jsr330.

core-common/src/main/java/org/mapstruct/DecoratedWith.java

@@ -123,9 +123,9 @@ import java.lang.annotation.Target;
  * <p>
  * JSR 330 doesn't specify qualifiers and only allows to specifically name the beans. Hence, the generated
  * implementation of the original mapper is annotated with {@code @Named("fully-qualified-name-of-generated-impl")}
- * (please note that when using a decorator, the class name of the mapper implementation ends with an underscore). To
- * inject that bean in your decorator, add the same annotation to the delegate field (e.g. by copy/pasting it from the
- * generated class):
+ * and {@code @Singleton} (please note that when using a decorator, the class name of the mapper implementation ends
+ * with an underscore). To inject that bean in your decorator, add the same annotation to the delegate field (e.g. by
+ * copy/pasting it from the generated class):
  *
  * <pre>
  * public abstract class PersonMapperDecorator implements PersonMapper {

core-common/src/main/java/org/mapstruct/Mapper.java

@@ -75,7 +75,7 @@ public @interface Mapper {
      * can be retrieved via {@code @Autowired}</li>
      * <li>
      * {@code jsr330}: the generated mapper is annotated with {@code @Named} and
-     * can be retrieved via {@code @Inject}</li>
+     * {@code @Singleton}, and can be retrieved via {@code @Inject}</li>
      * </ul>
      * The method overrides an unmappedTargetPolicy set in a central configuration set
      * by {@link #config() }

core-common/src/main/java/org/mapstruct/MapperConfig.java

@@ -77,7 +77,7 @@ public @interface MapperConfig {
      * can be retrieved via {@code @Autowired}</li>
      * <li>
      * {@code jsr330}: the generated mapper is annotated with {@code @Named} and
-     * can be retrieved via {@code @Inject}</li>
+     * {@code @Singleton}, and can be retrieved via {@code @Inject}</li>
      * </ul>
      *
      * @return The component model for the generated mapper.

integrationtest/src/test/resources/jsr330Test/src/main/java/org/mapstruct/itest/jsr330/other/DateMapper.java

@@ -23,7 +23,9 @@ import java.text.SimpleDateFormat;
 import java.util.Date;
 
 import javax.inject.Named;
+import javax.inject.Singleton;
 
+@Singleton
 @Named
 public class DateMapper {
 

processor/src/main/java/org/mapstruct/ap/internal/processor/Jsr330ComponentProcessor.java

@@ -42,16 +42,16 @@ public class Jsr330ComponentProcessor extends AnnotationBasedComponentModelProce
     @Override
     protected List<Annotation> getTypeAnnotations(Mapper mapper) {
         if ( mapper.getDecorator() == null ) {
-            return Collections.singletonList( named() );
+            return Arrays.asList( singleton(), named() );
         }
         else {
-            return Collections.singletonList( namedDelegate( mapper ) );
+            return Arrays.asList( singleton(), namedDelegate( mapper ) );
         }
     }
 
     @Override
     protected List<Annotation> getDecoratorAnnotations() {
-        return Collections.singletonList( named() );
+        return Arrays.asList( singleton(), named() );
     }
 
     @Override
@@ -69,6 +69,10 @@ public class Jsr330ComponentProcessor extends AnnotationBasedComponentModelProce
         return true;
     }
 
+    private Annotation singleton() {
+        return new Annotation( getTypeFactory().getType( "javax.inject.Singleton" ) );
+    }
+
     private Annotation named() {
         return new Annotation( getTypeFactory().getType( "javax.inject.Named" ) );
     }