Allow package-private mapper

Use and make the default constructor accessible to create the mapper
instance. 

fixes #1365

core-common/src/main/java/org/mapstruct/factory/Mappers.java

@@ -18,6 +18,8 @@
  */
 package org.mapstruct.factory;
 
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.ServiceLoader;
@@ -78,10 +80,13 @@ public class Mappers {
         catch ( ClassNotFoundException e ) {
             throw new RuntimeException( e );
         }
+        catch ( NoSuchMethodException e) {
+            throw new RuntimeException( e );
+        }
     }
 
-    private static <T> T getMapper(
+    private static <T> T getMapper(Class<T> mapperType, Iterable<ClassLoader> classLoaders)
-            Class<T> mapperType, Iterable<ClassLoader> classLoaders) throws ClassNotFoundException {
+            throws ClassNotFoundException, NoSuchMethodException {
 
         for ( ClassLoader classLoader : classLoaders ) {
             T mapper = doGetMapper( mapperType, classLoader );
@@ -93,11 +98,13 @@ public class Mappers {
         throw new ClassNotFoundException("Cannot find implementation for " + mapperType.getName() );
     }
 
-    private static <T> T doGetMapper(Class<T> clazz, ClassLoader classLoader) {
+    private static <T> T doGetMapper(Class<T> clazz, ClassLoader classLoader) throws NoSuchMethodException {
         try {
-            @SuppressWarnings("unchecked")
+            @SuppressWarnings( "unchecked" )
-            T mapper = (T) classLoader.loadClass( clazz.getName() + IMPLEMENTATION_SUFFIX ).newInstance();
+            Class<T> implementation = (Class<T>) classLoader.loadClass( clazz.getName() + IMPLEMENTATION_SUFFIX );
-            return mapper;
+            Constructor<T> constructor = implementation.getDeclaredConstructor();
+            constructor.setAccessible( true );
+            return constructor.newInstance();
         }
         catch (ClassNotFoundException e) {
             ServiceLoader<T> loader = ServiceLoader.load( clazz, classLoader );
@@ -118,5 +125,8 @@ public class Mappers {
         catch (IllegalAccessException e) {
             throw new RuntimeException( e );
         }
+        catch (InvocationTargetException e) {
+            throw new RuntimeException( e );
+        }
     }
 }

core-common/src/test/java/org/mapstruct/factory/MappersTest.java

@@ -47,4 +47,9 @@ public class MappersTest {
         assertThat( Mappers.getMapper( SomeClass.Foo.class ) ).isNotNull();
         assertThat( Mappers.getMapper( SomeClass.NestedClass.Foo.class ) ).isNotNull();
     }
+
+    @Test
+    public void shouldReturnPackagePrivateImplementationInstance() {
+        assertThat( Mappers.getMapper( PackagePrivateMapper.class ) ).isNotNull();
+    }
 }

core-common/src/test/java/org/mapstruct/factory/PackagePrivateMapper.java

@@ -0,0 +1,23 @@
+/**
+ *  Copyright 2012-2017 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.factory;
+
+interface PackagePrivateMapper {
+
+}

core-common/src/test/java/org/mapstruct/factory/PackagePrivateMapperImpl.java

@@ -0,0 +1,22 @@
+/**
+ *  Copyright 2012-2017 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.factory;
+
+class PackagePrivateMapperImpl implements PackagePrivateMapper {
+}