#295 NullValueMapping for IterableMapping on mapping method level

processor/src/main/java/org/mapstruct/ap/model/IterableMappingMethod.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.SetterWrapper;
 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;
 
 /**
@@ -42,6 +45,8 @@ public class IterableMappingMethod extends MappingMethod {
     private final Assignment elementAssignment;
     private final MethodReference factoryMethod;
     private final boolean overridden;
+    private final boolean mapNullToDefault;
+    private final TypeFactory typeFactory;
 
     public static class Builder {
 
@@ -102,17 +107,30 @@ public class IterableMappingMethod extends MappingMethod {
             // target accessor is setter, so decorate assignment as setter
             assignment = new SetterWrapper( assignment, method.getThrownTypes() );
 
+            // mapNullToDefault
+            MapNullToDefaultPrism prism = MapNullToDefaultPrism.getInstanceOn( method.getExecutable() );
+            boolean mapNullToDefault = ( prism != null ) && prism.value();
+
             MethodReference factoryMethod = AssignmentFactory.createFactoryMethod( method.getReturnType(), ctx );
-            return new IterableMappingMethod( method, assignment, factoryMethod );
+            return new IterableMappingMethod(
+                    method,
+                    assignment,
+                    factoryMethod,
+                    mapNullToDefault,
+                    ctx.getTypeFactory()
+            );
         }
     }
 
 
-    private IterableMappingMethod(Method method, Assignment parameterAssignment, MethodReference factoryMethod) {
+    private IterableMappingMethod(Method method, Assignment parameterAssignment, MethodReference factoryMethod,
+            boolean mapNullToDefault, TypeFactory typeFactory ) {
         super( method );
         this.elementAssignment = parameterAssignment;
         this.factoryMethod = factoryMethod;
         this.overridden = method.overridesMethod();
+        this.mapNullToDefault = mapNullToDefault;
+        this.typeFactory = typeFactory;
     }
 
     public Parameter getSourceParameter() {
@@ -137,9 +155,21 @@ public class IterableMappingMethod extends MappingMethod {
             types.addAll( elementAssignment.getImportTypes() );
         }
 
+        if (mapNullToDefault) {
+            types.add( typeFactory.getType( Collections.class ) );
+        }
+
         return types;
     }
 
+    public boolean isMapNullToDefault() {
+        return mapNullToDefault;
+    }
+
+    public boolean isOverridden() {
+        return overridden;
+    }
+
     public String getLoopVariableName() {
         return Strings.getSaveVariableName(
             getSourceParameter().getType().getTypeParameters().get( 0 ).getName(),
@@ -190,7 +220,4 @@ public class IterableMappingMethod extends MappingMethod {
         return true;
     }
 
-    public boolean isOverridden() {
-        return overridden;
-    }
 }

processor/src/main/resources/org.mapstruct.ap.model.IterableMappingMethod.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}>emptyList();
+        </#if>
     }
 
     <#if existingInstanceMapping>

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

@@ -18,6 +18,7 @@
  */
 package org.mapstruct.ap.test.mapnulltodefault;
 
+import java.util.List;
 import java.util.UUID;
 
 import org.mapstruct.Mapper;
@@ -50,4 +51,7 @@ public interface CarMapper {
     CarDto carToCarDto(Car car, String model);
 
 
+    @MapNullToDefault
+    List<CarDto> carsToCarDtos(List<Car> cars);
+
 }

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

@@ -18,6 +18,8 @@
  */
 package org.mapstruct.ap.test.mapnulltodefault;
 
+import java.util.Arrays;
+import java.util.List;
 import static org.fest.assertions.Assertions.assertThat;
 
 
@@ -67,7 +69,7 @@ public class CarMapperTest {
         assertThat( carDto2.getCatalogId() ).isNotEmpty();
     }
 
-   @Test
+    @Test
     public void shouldMapExpressionAndConstantRegardlessNullArgSeveralSources() {
         //given
         Car car = new Car( "Morris", 2 );
@@ -92,4 +94,25 @@ public class CarMapperTest {
         assertThat( carDto2.getCatalogId() ).isNotEmpty();
     }
 
+    @Test
+    public void shouldMapIterableWithNullArg() {
+
+        //given
+        Car car = new Car( "Morris", 2 );
+
+        //when
+        List<CarDto> carDtos1 = CarMapper.INSTANCE.carsToCarDtos( Arrays.asList( car ) );
+
+       //then
+       assertThat( carDtos1 ).isNotNull();
+       assertThat( carDtos1.size() ).isEqualTo( 1 );
+
+       //when
+       List<CarDto> carDtos2 = CarMapper.INSTANCE.carsToCarDtos( null );
+
+       //then
+       assertThat( carDtos2 ).isNotNull();
+       assertThat( carDtos2.isEmpty() ).isTrue();
+
+    }
 }