#163 Adding support for decorators

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

@@ -0,0 +1,56 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Specifies a decorator to be applied to a generated mapper, which e.g. can be used to amend mappings performed by
+ * generated mapping methods.
+ * <p>
+ * A typical decorator implementation will be an abstract class and only implement/override a subset of the methods of
+ * the mapper type which it decorates. All methods not implemented or overridden by the decorator will be implemented by
+ * the code generator.
+ * <p>
+ * If a constructor with a single parameter accepting the type of the decorated mapper is present, a delegate with
+ * generated implementations of all the mapper methods will be passed to this constructor. A typical implementation will
+ * store the passed delegate in a field of the decorator and make use of it in the decorator methods.
+ * <p>
+ * <b>NOTE:</b> The decorator feature is considered experimental and it may change in future releases. Currently
+ * decorators are only supported for the default component model, not for the CDI and Spring models.
+ *
+ * @author Gunnar Morling
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface DecoratedWith {
+
+    /**
+     * The decorator type. Must extend or implement the mapper type to which it is applied.
+     * <p>
+     * The decorator type must either have a default constructor or a constructor with a single parameter accepting the
+     * type of the decorated mapper.
+     *
+     * @return the decorator type
+     */
+    Class<?> value();
+}

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

@@ -0,0 +1,88 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.model;
+
+import java.util.Arrays;
+import java.util.List;
+import javax.lang.model.element.ElementKind;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.util.Elements;
+
+import org.mapstruct.ap.model.common.Accessibility;
+import org.mapstruct.ap.model.common.ModelElement;
+import org.mapstruct.ap.model.common.Type;
+import org.mapstruct.ap.model.common.TypeFactory;
+import org.mapstruct.ap.prism.DecoratedWithPrism;
+
+/**
+ * Represents a decorator applied to a generated mapper type.
+ *
+ * @author Gunnar Morling
+ */
+public class Decorator extends GeneratedType {
+
+    private static final String IMPLEMENTATION_SUFFIX = "Impl";
+
+    private Decorator(TypeFactory typeFactory, String packageName, String name, String superClassName,
+                      String interfaceName, List<MappingMethod> methods, List<? extends ModelElement> fields,
+                      boolean suppressGeneratorTimestamp, Accessibility accessibility) {
+        super(
+            typeFactory,
+            packageName,
+            name,
+            superClassName,
+            interfaceName,
+            methods,
+            fields,
+            suppressGeneratorTimestamp,
+            accessibility
+        );
+    }
+
+    public static Decorator getInstance(Elements elementUtils, TypeFactory typeFactory, TypeElement mapperElement,
+                                        DecoratedWithPrism decoratorPrism, List<MappingMethod> methods,
+                                        boolean hasDelegateConstructor,
+                                        boolean suppressGeneratorTimestamp) {
+        Type decoratorType = typeFactory.getType( decoratorPrism.value() );
+
+        return new Decorator(
+            typeFactory,
+            elementUtils.getPackageOf( mapperElement ).getQualifiedName().toString(),
+            mapperElement.getSimpleName().toString() + IMPLEMENTATION_SUFFIX,
+            decoratorType.getName(),
+            mapperElement.getKind() == ElementKind.INTERFACE ? mapperElement.getSimpleName().toString() : null,
+            methods,
+            Arrays.asList(
+                new Field( typeFactory.getType( mapperElement ), "delegate" ),
+                new DecoratorConstructor(
+                    mapperElement.getSimpleName().toString() + IMPLEMENTATION_SUFFIX,
+                    mapperElement.getSimpleName().toString() + "Impl_",
+                    hasDelegateConstructor
+                )
+            ),
+            suppressGeneratorTimestamp,
+            Accessibility.fromModifiers( mapperElement.getModifiers() )
+        );
+    }
+
+    @Override
+    protected String getTemplateName() {
+        return GeneratedType.class.getName() + ".ftl";
+    }
+}

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

@@ -0,0 +1,60 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.model;
+
+import java.util.Collections;
+import java.util.Set;
+
+import org.mapstruct.ap.model.common.ModelElement;
+import org.mapstruct.ap.model.common.Type;
+
+/**
+ * Represents the constructor of a decorator.
+ *
+ * @author Gunnar Morling
+ */
+public class DecoratorConstructor extends ModelElement {
+
+    private final String name;
+    private final String delegateName;
+    private final boolean invokeSuperConstructor;
+
+    public DecoratorConstructor(String name, String delegateName, boolean invokeSuperConstructor) {
+        this.name = name;
+        this.delegateName = delegateName;
+        this.invokeSuperConstructor = invokeSuperConstructor;
+    }
+
+    @Override
+    public Set<Type> getImportTypes() {
+        return Collections.emptySet();
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getDelegateName() {
+        return delegateName;
+    }
+
+    public boolean isInvokeSuperConstructor() {
+        return invokeSuperConstructor;
+    }
+}

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

@@ -0,0 +1,33 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.model;
+
+import org.mapstruct.ap.model.source.Method;
+
+/**
+ * A method of a decorator which delegates to the corresponding method of the generated mapper implementation.
+ *
+ * @author Gunnar Morling
+ */
+public class DelegatingMethod extends MappingMethod {
+
+    public DelegatingMethod(Method method) {
+        super( method );
+    }
+}

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

@@ -35,13 +35,15 @@ import org.mapstruct.ap.model.common.TypeFactory;
 public class Mapper extends GeneratedType {
 
     private static final String IMPLEMENTATION_SUFFIX = "Impl";
+    private static final String DECORATED_IMPLEMENTATION_SUFFIX = "Impl_";
 
     private final List<MapperReference> referencedMappers;
+    private final Decorator decorator;
 
     private Mapper(TypeFactory typeFactory, String packageName, String name, String superClassName,
                    String interfaceName,
                    List<MappingMethod> methods, boolean suppressGeneratorTimestamp, Accessibility accessibility,
-                   List<MapperReference> referencedMappers) {
+                   List<MapperReference> referencedMappers, Decorator decorator) {
 
         super(
             typeFactory,
@@ -56,6 +58,7 @@ public class Mapper extends GeneratedType {
         );
 
         this.referencedMappers = referencedMappers;
+        this.decorator = decorator;
     }
 
     public static class Builder {
@@ -67,6 +70,7 @@ public class Mapper extends GeneratedType {
 
         private Elements elementUtils;
         private boolean suppressGeneratorTimestamp;
+        private Decorator decorator;
 
         public Builder element(TypeElement element) {
             this.element = element;
@@ -98,8 +102,14 @@ public class Mapper extends GeneratedType {
             return this;
         }
 
+        public Builder decorator(Decorator decorator) {
+            this.decorator = decorator;
+            return this;
+        }
+
         public Mapper build() {
-            String implementationName = element.getSimpleName() + IMPLEMENTATION_SUFFIX;
+            String implementationName = element.getSimpleName()
+                + ( decorator == null ? IMPLEMENTATION_SUFFIX : DECORATED_IMPLEMENTATION_SUFFIX );
 
             return new Mapper(
                 typeFactory,
@@ -110,7 +120,8 @@ public class Mapper extends GeneratedType {
                 mappingMethods,
                 suppressGeneratorTimestamp,
                 Accessibility.fromModifiers( element.getModifiers() ),
-                mapperReferences
+                mapperReferences,
+                decorator
             );
         }
     }
@@ -119,6 +130,10 @@ public class Mapper extends GeneratedType {
         return referencedMappers;
     }
 
+    public Decorator getDecorator() {
+        return decorator;
+    }
+
     @Override
     protected String getTemplateName() {
         return GeneratedType.class.getName() + ".ftl";

processor/src/main/java/org/mapstruct/ap/prism/PrismGenerator.java

@@ -19,16 +19,17 @@
 package org.mapstruct.ap.prism;
 
 import javax.xml.bind.annotation.XmlElementDecl;
+
 import net.java.dev.hickory.prism.GeneratePrism;
 import net.java.dev.hickory.prism.GeneratePrisms;
-
+import org.mapstruct.DecoratedWith;
 import org.mapstruct.IterableMapping;
 import org.mapstruct.MapMapping;
 import org.mapstruct.Mapper;
 import org.mapstruct.Mapping;
 import org.mapstruct.MappingTarget;
-import org.mapstruct.TargetType;
 import org.mapstruct.Mappings;
+import org.mapstruct.TargetType;
 
 /**
  * Triggers the generation of prism types using <a href="https://java.net/projects/hickory">Hickory</a>.
@@ -43,6 +44,7 @@ import org.mapstruct.Mappings;
     @GeneratePrism(value = MapMapping.class, publicAccess = true),
     @GeneratePrism(value = TargetType.class, publicAccess = true),
     @GeneratePrism(value = MappingTarget.class, publicAccess = true),
+    @GeneratePrism(value = DecoratedWith.class, publicAccess = true),
 
     // external types
     @GeneratePrism(value = XmlElementDecl.class, publicAccess = true)

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

@@ -32,6 +32,7 @@ import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.TypeElement;
 import javax.lang.model.type.TypeKind;
 import javax.lang.model.type.TypeMirror;
+import javax.lang.model.util.ElementFilter;
 import javax.lang.model.util.Elements;
 import javax.lang.model.util.Types;
 import javax.tools.Diagnostic.Kind;
@@ -39,7 +40,9 @@ import javax.tools.Diagnostic.Kind;
 import org.mapstruct.ap.conversion.ConversionProvider;
 import org.mapstruct.ap.conversion.Conversions;
 import org.mapstruct.ap.model.BeanMappingMethod;
+import org.mapstruct.ap.model.Decorator;
 import org.mapstruct.ap.model.DefaultMapperReference;
+import org.mapstruct.ap.model.DelegatingMethod;
 import org.mapstruct.ap.model.EnumMappingMethod;
 import org.mapstruct.ap.model.IterableMappingMethod;
 import org.mapstruct.ap.model.MapMappingMethod;
@@ -64,6 +67,7 @@ import org.mapstruct.ap.model.source.builtin.BuiltInMethod;
 import org.mapstruct.ap.model.source.selector.MethodSelectors;
 import org.mapstruct.ap.option.Options;
 import org.mapstruct.ap.option.ReportingPolicy;
+import org.mapstruct.ap.prism.DecoratedWithPrism;
 import org.mapstruct.ap.prism.MapperPrism;
 import org.mapstruct.ap.util.Executables;
 import org.mapstruct.ap.util.Filters;
@@ -127,6 +131,7 @@ public class MapperCreationProcessor implements ModelElementProcessor<List<Sourc
             .mappingMethods( mappingMethods )
             .mapperReferences( mapperReferences )
             .suppressGeneratorTimestamp( options.isSuppressGeneratorTimestamp() )
+            .decorator( getDecorator( element, methods ) )
             .typeFactory( typeFactory )
             .elementUtils( elementUtils )
             .build();
@@ -159,6 +164,70 @@ public class MapperCreationProcessor implements ModelElementProcessor<List<Sourc
         }
     }
 
+    private Decorator getDecorator(TypeElement element, List<SourceMethod> methods) {
+        DecoratedWithPrism decoratorPrism = DecoratedWithPrism.getInstanceOn( element );
+
+        if ( decoratorPrism == null ) {
+            return null;
+        }
+
+        TypeElement decoratorElement = (TypeElement) typeUtils.asElement( decoratorPrism.value() );
+
+        List<MappingMethod> mappingMethods = new ArrayList<MappingMethod>( methods.size() );
+
+        for ( SourceMethod mappingMethod : methods ) {
+            boolean implementationRequired = true;
+            for ( ExecutableElement method : ElementFilter.methodsIn( decoratorElement.getEnclosedElements() ) ) {
+                if ( elementUtils.overrides( method, mappingMethod.getExecutable(), decoratorElement ) ) {
+                    implementationRequired = false;
+                    break;
+                }
+            }
+
+            if ( implementationRequired ) {
+                mappingMethods.add( new DelegatingMethod( mappingMethod ) );
+            }
+        }
+
+        boolean hasDelegateConstructor = false;
+        boolean hasDefaultConstructor = false;
+        for ( ExecutableElement constructor : ElementFilter.constructorsIn( decoratorElement.getEnclosedElements() ) ) {
+            if ( constructor.getParameters().isEmpty() ) {
+                hasDefaultConstructor = true;
+            }
+            else if ( constructor.getParameters().size() == 1 ) {
+                if ( typeUtils.isAssignable(
+                    element.asType(),
+                    constructor.getParameters().iterator().next().asType()
+                ) ) {
+                    hasDelegateConstructor = true;
+                }
+            }
+        }
+
+        if ( !hasDelegateConstructor && !hasDefaultConstructor ) {
+            messager.printMessage(
+                Kind.ERROR,
+                String.format(
+                    "Specified decorator type has no default constructor nor a constructor with a single " +
+                        "parameter accepting the decorated mapper type."
+                ),
+                element,
+                decoratorPrism.mirror
+            );
+        }
+
+        return Decorator.getInstance(
+            elementUtils,
+            typeFactory,
+            element,
+            decoratorPrism,
+            mappingMethods,
+            hasDelegateConstructor,
+            options.isSuppressGeneratorTimestamp()
+        );
+    }
+
     private List<MapperReference> getReferencedMappers(TypeElement element) {
         List<MapperReference> mapperReferences = new LinkedList<MapperReference>();
         List<String> variableNames = new LinkedList<String>();

processor/src/main/java/org/mapstruct/ap/processor/MapperRenderingProcessor.java

@@ -48,6 +48,10 @@ public class MapperRenderingProcessor implements ModelElementProcessor<Mapper, V
         ModelWriter modelWriter = new ModelWriter();
 
         createSourceFile( model, modelWriter, filer );
+
+        if ( model.getDecorator() != null ) {
+            createSourceFile( model.getDecorator(), modelWriter, filer );
+        }
     }
 
     private void createSourceFile(GeneratedType model, ModelWriter modelWriter, Filer filer) {

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

@@ -0,0 +1,26 @@
+<#--
+
+     Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+     and/or other contributors as indicated by the @authors tag. See the
+     copyright.txt file in the distribution for a full listing of all
+     contributors.
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+
+-->
+public ${name}() {
+    <#if invokeSuperConstructor>
+    super( new ${delegateName}() );
+    </#if>
+    this.delegate = new ${delegateName}();
+}

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

@@ -0,0 +1,24 @@
+<#--
+
+     Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+     and/or other contributors as indicated by the @authors tag. See the
+     copyright.txt file in the distribution for a full listing of all
+     contributors.
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+
+-->
+@Override
+public <@includeModel object=returnType/> ${name}(<#list parameters as param><@includeModel object=param/><#if param_has_next>, </#if></#list>) {
+    return delegate.${name}( <#list parameters as param>${param.name}<#if param_has_next>, </#if></#list> );
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/Address.java

@@ -0,0 +1,36 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+public class Address {
+
+    private String addressLine;
+
+    public Address(String addressLine) {
+        this.addressLine = addressLine;
+    }
+
+    public String getAddressLine() {
+        return addressLine;
+    }
+
+    public void setAddressLine(String addressLine) {
+        this.addressLine = addressLine;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/AddressDto.java

@@ -0,0 +1,32 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+public class AddressDto {
+
+    private String addressLine;
+
+    public String getAddressLine() {
+        return addressLine;
+    }
+
+    public void setAddressLine(String addressLine) {
+        this.addressLine = addressLine;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/AnotherPersonMapper.java

@@ -0,0 +1,35 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+import org.mapstruct.DecoratedWith;
+import org.mapstruct.Mapper;
+import org.mapstruct.ReportingPolicy;
+import org.mapstruct.factory.Mappers;
+
+@Mapper(unmappedTargetPolicy = ReportingPolicy.IGNORE)
+@DecoratedWith(AnotherPersonMapperDecorator.class)
+public interface AnotherPersonMapper {
+
+    AnotherPersonMapper INSTANCE = Mappers.getMapper( AnotherPersonMapper.class );
+
+    PersonDto personToPersonDto(Person person);
+
+    AddressDto addressToAddressDto(Address address);
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/AnotherPersonMapperDecorator.java

@@ -0,0 +1,35 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+public abstract class AnotherPersonMapperDecorator implements AnotherPersonMapper {
+
+    @Override
+    public PersonDto personToPersonDto(Person person) {
+        AddressDto addressDto = new AddressDto();
+        addressDto.setAddressLine( person.getAddress().getAddressLine() );
+
+        PersonDto dto = new PersonDto();
+        dto.setDateOfBirth( person.getDateOfBirth() );
+        dto.setName( person.getFirstName() + " " + person.getLastName() );
+        dto.setAddress( addressDto );
+
+        return dto;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/DecoratorTest.java

@@ -0,0 +1,123 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+import java.util.Calendar;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.MapperTestBase;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.testng.annotations.Test;
+
+import static org.fest.assertions.Assertions.assertThat;
+
+/**
+ * Test for the application of decorators.
+ *
+ * @author Gunnar Morling
+ */
+@WithClasses({
+    Person.class,
+    PersonDto.class,
+    Address.class,
+    AddressDto.class
+})
+@IssueKey("163")
+public class DecoratorTest extends MapperTestBase {
+
+    @Test
+    @WithClasses({
+        PersonMapper.class,
+        PersonMapperDecorator.class
+    })
+    public void shouldInvokeDecoratorMethods() {
+        //given
+        Calendar birthday = Calendar.getInstance();
+        birthday.set( 1928, 4, 23 );
+        Person person = new Person( "Gary", "Crant", birthday.getTime(), new Address( "42 Ocean View Drive" ) );
+
+        //when
+        PersonDto personDto = PersonMapper.INSTANCE.personToPersonDto( person );
+
+        //then
+        assertThat( personDto ).isNotNull();
+        assertThat( personDto.getName() ).isEqualTo( "Gary Crant" );
+        assertThat( personDto.getAddress() ).isNotNull();
+        assertThat( personDto.getAddress().getAddressLine() ).isEqualTo( "42 Ocean View Drive" );
+    }
+
+    @Test
+    @WithClasses({
+        PersonMapper.class,
+        PersonMapperDecorator.class
+    })
+    public void shouldDelegateNonDecoratedMethodsToDefaultImplementation() {
+        //given
+        Address address = new Address( "42 Ocean View Drive" );
+
+        //when
+        AddressDto addressDto = PersonMapper.INSTANCE.addressToAddressDto( address );
+
+        //then
+        assertThat( addressDto ).isNotNull();
+        assertThat( addressDto.getAddressLine() ).isEqualTo( "42 Ocean View Drive" );
+    }
+
+    @Test
+    @WithClasses({
+        AnotherPersonMapper.class,
+        AnotherPersonMapperDecorator.class
+    })
+    public void shouldApplyDecoratorWithDefaultConstructor() {
+        //given
+        Calendar birthday = Calendar.getInstance();
+        birthday.set( 1928, 4, 23 );
+        Person person = new Person( "Gary", "Crant", birthday.getTime(), new Address( "42 Ocean View Drive" ) );
+
+        //when
+        PersonDto personDto = AnotherPersonMapper.INSTANCE.personToPersonDto( person );
+
+        //then
+        assertThat( personDto ).isNotNull();
+        assertThat( personDto.getName() ).isEqualTo( "Gary Crant" );
+        assertThat( personDto.getAddress() ).isNotNull();
+        assertThat( personDto.getAddress().getAddressLine() ).isEqualTo( "42 Ocean View Drive" );
+    }
+
+    @Test
+    @WithClasses({
+        YetAnotherPersonMapper.class,
+        YetAnotherPersonMapperDecorator.class
+    })
+    public void shouldApplyDelegateToClassBasedMapper() {
+        //given
+        Calendar birthday = Calendar.getInstance();
+        birthday.set( 1928, 4, 23 );
+        Person person = new Person( "Gary", "Crant", birthday.getTime(), new Address( "42 Ocean View Drive" ) );
+
+        //when
+        PersonDto personDto = YetAnotherPersonMapper.INSTANCE.personToPersonDto( person );
+
+        //then
+        assertThat( personDto ).isNotNull();
+        assertThat( personDto.getName() ).isEqualTo( "Gary Crant" );
+        assertThat( personDto.getAddress() ).isNotNull();
+        assertThat( personDto.getAddress().getAddressLine() ).isEqualTo( "42 Ocean View Drive" );
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/Person.java

@@ -0,0 +1,68 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+import java.util.Date;
+
+public class Person {
+
+    private String firstName;
+    private String lastName;
+    private Date dateOfBirth;
+    private Address address;
+
+    public Person(String firstName, String lastName, Date dateOfBirth, Address address) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.dateOfBirth = dateOfBirth;
+        this.address = address;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public Date getDateOfBirth() {
+        return dateOfBirth;
+    }
+
+    public void setDateOfBirth(Date dateOfBirth) {
+        this.dateOfBirth = dateOfBirth;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/PersonDto.java

@@ -0,0 +1,52 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+import java.util.Date;
+
+public class PersonDto {
+
+    private String name;
+    private Date dateOfBirth;
+    private AddressDto address;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public Date getDateOfBirth() {
+        return dateOfBirth;
+    }
+
+    public void setDateOfBirth(Date dateOfBirth) {
+        this.dateOfBirth = dateOfBirth;
+    }
+
+    public AddressDto getAddress() {
+        return address;
+    }
+
+    public void setAddress(AddressDto address) {
+        this.address = address;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/PersonMapper.java

@@ -0,0 +1,35 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+import org.mapstruct.DecoratedWith;
+import org.mapstruct.Mapper;
+import org.mapstruct.ReportingPolicy;
+import org.mapstruct.factory.Mappers;
+
+@Mapper(unmappedTargetPolicy = ReportingPolicy.IGNORE)
+@DecoratedWith(PersonMapperDecorator.class)
+public interface PersonMapper {
+
+    PersonMapper INSTANCE = Mappers.getMapper( PersonMapper.class );
+
+    PersonDto personToPersonDto(Person person);
+
+    AddressDto addressToAddressDto(Address address);
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/PersonMapperDecorator.java

@@ -0,0 +1,36 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+public abstract class PersonMapperDecorator implements PersonMapper {
+
+    private final PersonMapper delegate;
+
+    public PersonMapperDecorator(PersonMapper delegate) {
+        this.delegate = delegate;
+    }
+
+    @Override
+    public PersonDto personToPersonDto(Person person) {
+        PersonDto dto = delegate.personToPersonDto( person );
+        dto.setName( person.getFirstName() + " " + person.getLastName() );
+
+        return dto;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/YetAnotherPersonMapper.java

@@ -0,0 +1,35 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+import org.mapstruct.DecoratedWith;
+import org.mapstruct.Mapper;
+import org.mapstruct.ReportingPolicy;
+import org.mapstruct.factory.Mappers;
+
+@Mapper(unmappedTargetPolicy = ReportingPolicy.IGNORE)
+@DecoratedWith(YetAnotherPersonMapperDecorator.class)
+public abstract class YetAnotherPersonMapper {
+
+    public static final YetAnotherPersonMapper INSTANCE = Mappers.getMapper( YetAnotherPersonMapper.class );
+
+    public abstract PersonDto personToPersonDto(Person person);
+
+    public abstract AddressDto addressToAddressDto(Address address);
+}

processor/src/test/java/org/mapstruct/ap/test/decorator/YetAnotherPersonMapperDecorator.java

@@ -0,0 +1,35 @@
+/**
+ *  Copyright 2012-2014 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.decorator;
+
+public abstract class YetAnotherPersonMapperDecorator extends YetAnotherPersonMapper {
+
+    @Override
+    public PersonDto personToPersonDto(Person person) {
+        AddressDto addressDto = new AddressDto();
+        addressDto.setAddressLine( person.getAddress().getAddressLine() );
+
+        PersonDto dto = new PersonDto();
+        dto.setDateOfBirth( person.getDateOfBirth() );
+        dto.setName( person.getFirstName() + " " + person.getLastName() );
+        dto.setAddress( addressDto );
+
+        return dto;
+    }
+}