highly WIP

processor/src/main/java/org/mapstruct/ap/internal/model/IterableMappingMethod.java

@@ -5,8 +5,7 @@
  */
 package org.mapstruct.ap.internal.model;
 
-import static org.mapstruct.ap.internal.util.Collections.first;
+import java.util.ArrayList;
-
 import java.util.Collection;
 import java.util.List;
 import java.util.Set;
@@ -14,10 +13,13 @@ import java.util.Set;
 import org.mapstruct.ap.internal.model.assignment.LocalVarWrapper;
 import org.mapstruct.ap.internal.model.assignment.SetterWrapper;
 import org.mapstruct.ap.internal.model.common.Assignment;
+import org.mapstruct.ap.internal.model.common.ParameterBinding;
 import org.mapstruct.ap.internal.model.common.Type;
 import org.mapstruct.ap.internal.model.source.Method;
 import org.mapstruct.ap.internal.model.source.SelectionParameters;
 
+import static org.mapstruct.ap.internal.util.Collections.first;
+
 /**
  * A {@link MappingMethod} implemented by a {@link Mapper} class which maps one iterable type to another. The collection
  * elements are mapped either by a {@link TypeConversion} or another mapping method.
@@ -26,12 +28,21 @@ import org.mapstruct.ap.internal.model.source.SelectionParameters;
  */
 public class IterableMappingMethod extends ContainerMappingMethod {
 
+    private Method iterableConditionMethod;
+
     public static class Builder extends ContainerMappingMethodBuilder<Builder, IterableMappingMethod> {
 
+        private Method iterableConditionMethod;
+
         public Builder() {
             super( Builder.class, "collection element" );
         }
 
+        public Builder iterableConditionMethod(Method iterableConditionMethod) {
+            this.iterableConditionMethod = iterableConditionMethod;
+            return this;
+        }
+
         @Override
         protected Type getElementType(Type parameterType) {
             return parameterType.isArrayType() ? parameterType.getComponentType() : first(
@@ -65,17 +76,43 @@ public class IterableMappingMethod extends ContainerMappingMethod {
                 loopVariableName,
                 beforeMappingMethods,
                 afterMappingMethods,
-                selectionParameters
+                selectionParameters,
+                iterableConditionMethod
             );
         }
     }
 
+    public boolean hasIterableConditionMethod() {
+        return getIterableConditionMethod() != null;
+    }
+
+    public Method getIterableConditionMethod() {
+        return iterableConditionMethod;
+    }
+
+    public MethodReference getIterableConditionMethodReference() {
+
+        ArrayList<ParameterBinding> parameterBindings = new ArrayList<>();
+
+        parameterBindings.add(
+            ParameterBinding.fromTypeAndName(
+                iterableConditionMethod.getParameters().get( 0 ).getType(),
+                getLoopVariableName()
+            )
+        );
+
+        return MethodReference.forForgedMethod(
+            iterableConditionMethod,
+            parameterBindings
+        );
+    }
+
     private IterableMappingMethod(Method method, List<Annotation> annotations,
                                   Collection<String> existingVariables, Assignment parameterAssignment,
                                   MethodReference factoryMethod, boolean mapNullToDefault, String loopVariableName,
                                   List<LifecycleCallbackMethodReference> beforeMappingReferences,
                                   List<LifecycleCallbackMethodReference> afterMappingReferences,
-        SelectionParameters selectionParameters) {
+        SelectionParameters selectionParameters, Method iterableConditionMethod) {
         super(
             method,
             annotations,
@@ -88,6 +125,7 @@ public class IterableMappingMethod extends ContainerMappingMethod {
             afterMappingReferences,
             selectionParameters
         );
+        this.iterableConditionMethod = iterableConditionMethod;
     }
 
     @Override

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

@@ -25,6 +25,7 @@ import javax.lang.model.type.TypeMirror;
 import javax.lang.model.util.ElementFilter;
 
 import org.mapstruct.ap.internal.gem.BuilderGem;
+import org.mapstruct.ap.internal.gem.ConditionStrategyGem;
 import org.mapstruct.ap.internal.gem.DecoratedWithGem;
 import org.mapstruct.ap.internal.gem.InheritConfigurationGem;
 import org.mapstruct.ap.internal.gem.InheritInverseConfigurationGem;
@@ -340,10 +341,18 @@ public class MapperCreationProcessor implements ModelElementProcessor<List<Sourc
                 this.messager.note( 1, Message.ITERABLEMAPPING_CREATE_NOTE, method );
 
 
+                Method iterableConditionMethod = methods.stream()
+                    .filter( m -> m.getConditionOptions()
+                        .isStrategyApplicable( ConditionStrategyGem.ITERABLE_ELEMENTS ) )
+                    .findFirst()
+                    .orElse( null );
+
+                // TODO here are all methods - select them via MethodResolver (like PresenceCheckMethodResolver) and add it to the builder
                 IterableMappingMethod iterableMappingMethod = createWithElementMappingMethod(
                     method,
                     mappingOptions,
                     new IterableMappingMethod.Builder()
+                        .iterableConditionMethod( iterableConditionMethod )
                 );
 
                 hasFactoryMethod = iterableMappingMethod.getFactoryMethod() != null;

processor/src/main/resources/org/mapstruct/ap/internal/model/IterableMappingMethod.ftl

@@ -24,7 +24,6 @@
             <#if resultType.arrayType>
                 <#if existingInstanceMapping>
                     <#-- we can't clear an existing array, so we've got to clear by setting values to default -->
-                    // test
                         ${resultName}[${index2Name}] = ${resultElementType.null};
                     }
                     return<#if returnType.name != "void"> ${resultName}</#if>;
@@ -74,9 +73,13 @@
         }
     <#else>
         for ( <@includeModel object=sourceElementType/> ${loopVariableName} : ${sourceParameter.name} ) {
-            if ( countryIsNotNull( employeeDto ) ) {
+            <#if hasIterableConditionMethod()>
+                if ( <@includeModel object=iterableConditionMethodReference /> ) {
                 <@includeModel object=elementAssignment targetBeanName=resultName targetWriteAccessorName="add" targetType=resultElementType/>
-            }
+                }
+            <#else>
+                <@includeModel object=elementAssignment targetBeanName=resultName targetWriteAccessorName="add" targetType=resultElementType/>
+            </#if>
         }
     </#if>
     <#list afterMappingReferences as callback>