#295 NullValueMapping for MapMapping on mapping method level

processor/src/main/java/org/mapstruct/ap/model/MapMappingMethod.java

@@ -18,6 +18,7 @@
  */
 package org.mapstruct.ap.model;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 
@@ -28,7 +29,9 @@ import org.mapstruct.ap.model.assignment.Assignment;
 import org.mapstruct.ap.model.assignment.LocalVarWrapper;
 import org.mapstruct.ap.model.common.Parameter;
 import org.mapstruct.ap.model.common.Type;
+import org.mapstruct.ap.model.common.TypeFactory;
 import org.mapstruct.ap.model.source.Method;
+import org.mapstruct.ap.prism.MapNullToDefaultPrism;
 import org.mapstruct.ap.util.Strings;
 
 /**
@@ -43,6 +46,8 @@ public class MapMappingMethod extends MappingMethod {
     private final Assignment valueAssignment;
     private final MethodReference factoryMethod;
     private final boolean overridden;
+    private final boolean mapNullToDefault;
+    private final TypeFactory typeFactory;
 
     public static class Builder {
 
@@ -134,23 +139,36 @@ public class MapMappingMethod extends MappingMethod {
                 ctx.getMessager().printMessage( Diagnostic.Kind.ERROR, message, method.getExecutable() );
             }
 
+           // mapNullToDefault
+            MapNullToDefaultPrism prism = MapNullToDefaultPrism.getInstanceOn( method.getExecutable() );
+            boolean mapNullToDefault = ( prism != null ) && prism.value();
+
             MethodReference factoryMethod = AssignmentFactory.createFactoryMethod( method.getReturnType(), ctx );
 
             keyAssignment = new LocalVarWrapper( keyAssignment, method.getThrownTypes() );
             valueAssignment = new LocalVarWrapper( valueAssignment, method.getThrownTypes() );
 
-            return new MapMappingMethod( method, keyAssignment, valueAssignment, factoryMethod );
+            return new MapMappingMethod(
+                    method,
+                    keyAssignment,
+                    valueAssignment,
+                    factoryMethod,
+                    mapNullToDefault,
+                    ctx.getTypeFactory()
+            );
         }
     }
 
     private MapMappingMethod(Method method, Assignment keyAssignment, Assignment valueAssignment,
-                             MethodReference factoryMethod) {
+                             MethodReference factoryMethod,  boolean mapNullToDefault, TypeFactory typeFactory) {
         super( method );
 
         this.keyAssignment = keyAssignment;
         this.valueAssignment = valueAssignment;
         this.factoryMethod = factoryMethod;
         this.overridden = method.overridesMethod();
+        this.mapNullToDefault = mapNullToDefault;
+        this.typeFactory = typeFactory;
     }
 
     public Parameter getSourceParameter() {
@@ -182,6 +200,10 @@ public class MapMappingMethod extends MappingMethod {
             types.addAll( valueAssignment.getImportTypes() );
         }
 
+        if (mapNullToDefault) {
+            types.add( typeFactory.getType( Collections.class ) );
+        }
+
         return types;
     }
 
@@ -210,6 +232,14 @@ public class MapMappingMethod extends MappingMethod {
         return this.factoryMethod;
     }
 
+    public boolean isMapNullToDefault() {
+        return mapNullToDefault;
+    }
+
+    public boolean isOverridden() {
+        return overridden;
+    }
+
     @Override
     public int hashCode() {
         final int prime = 31;
@@ -249,7 +279,4 @@ public class MapMappingMethod extends MappingMethod {
         return true;
     }
 
-    public boolean isOverridden() {
-        return overridden;
-    }
 }

processor/src/main/resources/org.mapstruct.ap.model.MapMappingMethod.ftl

@@ -21,7 +21,11 @@
 <#if overridden>@Override</#if>
 <#lt>${accessibility.keyword} <@includeModel object=returnType /> ${name}(<#list parameters as param><@includeModel object=param/><#if param_has_next>, </#if></#list>) <@throws/> {
     if ( ${sourceParameter.name} == null ) {
+        <#if !mapNullToDefault>
         return<#if returnType.name != "void"> null</#if>;
+        <#else>
+        return Collections.<${resultType.typeParameters[0].name}, ${resultType.typeParameters[1].name}>emptyMap();
+        </#if>
     }
 
     <#if existingInstanceMapping>

processor/src/test/java/org/mapstruct/ap/test/mapnulltodefault/CarMapper.java

@@ -19,6 +19,7 @@
 package org.mapstruct.ap.test.mapnulltodefault;
 
 import java.util.List;
+import java.util.Map;
 import java.util.UUID;
 
 import org.mapstruct.Mapper;
@@ -54,4 +55,7 @@ public interface CarMapper {
     @MapNullToDefault
     List<CarDto> carsToCarDtos(List<Car> cars);
 
+
+    @MapNullToDefault
+    Map<Integer, CarDto> carsToCarDtoMap(Map<Integer, Car> cars);
 }

processor/src/test/java/org/mapstruct/ap/test/mapnulltodefault/CarMapperTest.java

@@ -19,7 +19,9 @@
 package org.mapstruct.ap.test.mapnulltodefault;
 
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import static org.fest.assertions.Assertions.assertThat;
 
 
@@ -115,4 +117,28 @@ public class CarMapperTest {
        assertThat( carDtos2.isEmpty() ).isTrue();
 
     }
+
+    @Test
+    public void shouldMapMapWithNullArg() {
+
+        //given
+        Car car = new Car( "Morris", 2 );
+        Map carMap = new HashMap();
+        carMap.put( 1, car);
+
+        //when
+        Map<Integer, CarDto> carDtoMap1 = CarMapper.INSTANCE.carsToCarDtoMap( carMap );
+
+       //then
+       assertThat( carDtoMap1 ).isNotNull();
+       assertThat( carDtoMap1.size() ).isEqualTo( 1 );
+
+       //when
+       Map<Integer, CarDto> carDtoMap2 = CarMapper.INSTANCE.carsToCarDtoMap( null );
+
+       //then
+       assertThat( carDtoMap2 ).isNotNull();
+       assertThat( carDtoMap2.isEmpty() ).isTrue();
+
+    }
 }