#32 Loading model element processors via service loader

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

@@ -18,7 +18,12 @@
  */
 package org.mapstruct.ap;
 
-import java.util.Arrays;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ServiceLoader;
 import java.util.Set;
 import javax.annotation.processing.AbstractProcessor;
 import javax.annotation.processing.ProcessingEnvironment;
@@ -39,11 +44,7 @@ import org.mapstruct.Mappings;
 import org.mapstruct.ap.model.Mapper;
 import org.mapstruct.ap.model.Options;
 import org.mapstruct.ap.model.ReportingPolicy;
-import org.mapstruct.ap.processor.CdiComponentProcessor;
 import org.mapstruct.ap.processor.DefaultModelElementProcessorContext;
-import org.mapstruct.ap.processor.MapperCreationProcessor;
-import org.mapstruct.ap.processor.MapperRenderingProcessor;
-import org.mapstruct.ap.processor.MethodRetrievalProcessor;
 import org.mapstruct.ap.processor.ModelElementProcessor;
 import org.mapstruct.ap.processor.ModelElementProcessor.ProcessorContext;
 
@@ -142,14 +143,31 @@ public class MappingProcessor extends AbstractProcessor {
         return processor.process( context, mapperTypeElement, sourceElement );
     }
 
-    //TODO Retrieve via service loader
+    /**
+     * Retrieves all model element processors, ordered by their priority value
+     * (with the method retrieval processor having the lowest priority value (1)
+     * and the code generation processor the highest priority value.
+     *
+     * @return A list with all model element processors.
+     */
     private Iterable<ModelElementProcessor<?, ?>> getProcessors() {
-        return Arrays.<ModelElementProcessor<?, ?>>asList(
+        // TODO Re-consider which class loader to use in case processors are
-            new MethodRetrievalProcessor(),
+        // loaded from other modules, too
-            new MapperCreationProcessor(),
+        @SuppressWarnings("rawtypes")
-            new CdiComponentProcessor(),
+        Iterator<ModelElementProcessor> processorIterator = ServiceLoader.load(
-            new MapperRenderingProcessor()
+            ModelElementProcessor.class,
-        );
+            MappingProcessor.class.getClassLoader()
+        )
+            .iterator();
+        List<ModelElementProcessor<?, ?>> processors = new ArrayList<ModelElementProcessor<?, ?>>();
+
+        while ( processorIterator.hasNext() ) {
+            processors.add( processorIterator.next() );
+        }
+
+        Collections.sort( processors, new ProcessorComparator() );
+
+        return processors;
     }
 
     private TypeElement asTypeElement(Element element) {
@@ -163,4 +181,15 @@ public class MappingProcessor extends AbstractProcessor {
             }, null
         );
     }
+
+    private static class ProcessorComparator implements Comparator<ModelElementProcessor<?, ?>> {
+
+        @Override
+        public int compare(ModelElementProcessor<?, ?> o1, ModelElementProcessor<?, ?> o2) {
+            return
+                o1.getPriority() < o2.getPriority() ? -1 :
+                    o1.getPriority() == o2.getPriority() ? 0 :
+                        1;
+        }
+    }
 }

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

@@ -56,4 +56,9 @@ public class CdiComponentProcessor implements ModelElementProcessor<Mapper, Mapp
 
         return mapper;
     }
+
+    @Override
+    public int getPriority() {
+        return 1100;
+    }
 }

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

@@ -93,6 +93,12 @@ public class MapperCreationProcessor implements ModelElementProcessor<List<Metho
         return getMapper( mapperTypeElement, sourceElement );
     }
 
+    @Override
+    public int getPriority() {
+        return 1000;
+    }
+
+
     private Mapper getMapper(TypeElement element, List<Method> methods) {
         ReportingPolicy unmappedTargetPolicy = getEffectiveUnmappedTargetPolicy( element );
         List<MappingMethod> mappingMethods = getMappingMethods( methods, unmappedTargetPolicy );

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

@@ -55,4 +55,9 @@ public class MapperRenderingProcessor implements ModelElementProcessor<Mapper, V
 
         new ModelWriter().writeModel( sourceFile, model );
     }
+
+    @Override
+    public int getPriority() {
+        return 10000;
+    }
 }

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

@@ -68,6 +68,11 @@ public class MethodRetrievalProcessor implements ModelElementProcessor<TypeEleme
         return retrieveMethods( mapperTypeElement, true );
     }
 
+    @Override
+    public int getPriority() {
+        return 1;
+    }
+
     /**
      * Retrieves the mapping methods declared by the given mapper type.
      *

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

@@ -77,4 +77,16 @@ public interface ModelElementProcessor<P, R> {
      *         generates the resulting Java source file.
      */
     R process(ProcessorContext context, TypeElement mapperTypeElement, P sourceElement);
+
+    /**
+     * Returns the priority value of this processor which must be between 1
+     * (highest priority) and 10000 (lowest priority). Processors are invoked in
+     * order from highest to lowest priority, starting with the mapping method
+     * retrieval processor (priority 1) and finishing with the code generation
+     * processor (priority 10000). Processors working on the built
+     * {@code Mapper} model must have a priority > 1000.
+     *
+     * @return The priority value of this processor.
+     */
+    int getPriority();
 }

processor/src/main/resources/META-INF/services/javax.annotation.processing.Processor

@@ -1 +1,18 @@
-org.mapstruct.ap.MappingProcessor
+# Copyright 2012-2013 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.
+
+org.mapstruct.ap.MappingProcessor

processor/src/main/resources/META-INF/services/org.mapstruct.ap.processor.ModelElementProcessor

@@ -0,0 +1,21 @@
+# Copyright 2012-2013 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.
+
+org.mapstruct.ap.processor.CdiComponentProcessor
+org.mapstruct.ap.processor.MapperCreationProcessor
+org.mapstruct.ap.processor.MapperRenderingProcessor
+org.mapstruct.ap.processor.MethodRetrievalProcessor