issue-#321 : Mybatis doesn't get correct return type when the mapper interface extends another one.

src/main/java/org/apache/ibatis/builder/annotation/MapperAnnotationBuilder.java

@@ -18,20 +18,8 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.lang.annotation.Annotation;
-import java.lang.reflect.Array;
-import java.lang.reflect.GenericArrayType;
-import java.lang.reflect.Method;
-import java.lang.reflect.ParameterizedType;
-import java.lang.reflect.Type;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.Iterator;
-import java.util.List;
-import java.util.Locale;
-import java.util.Map;
-import java.util.Set;
+import java.lang.reflect.*;
+import java.util.*;
 
 import org.apache.ibatis.annotations.Arg;
 import org.apache.ibatis.annotations.CacheNamespace;
@@ -94,12 +82,14 @@ public class MapperAnnotationBuilder {
   private Configuration configuration;
   private MapperBuilderAssistant assistant;
   private Class<?> type;
+  private Map<String, Map<String, Type>> parentTypeMap = new HashMap<String,Map<String,Type>>();
 
   public MapperAnnotationBuilder(Configuration configuration, Class<?> type) {
     String resource = type.getName().replace('.', '/') + ".java (best guess)";
     this.assistant = new MapperBuilderAssistant(configuration, resource);
     this.configuration = configuration;
     this.type = type;
+    collectTypeParameters(type);
 
     sqlAnnotationTypes.add(Select.class);
     sqlAnnotationTypes.add(Insert.class);
@@ -364,7 +354,7 @@ private Class<?> getParameterType(Method method) {
   }
 
   private Class<?> getReturnType(Method method) {
-    Class<?> returnType = method.getReturnType();
+    Class<?> returnType = resolveReturnType(method);
     // issue #508
     if (void.class.equals(returnType)) {
       ResultType rt = method.getAnnotation(ResultType.class);
@@ -386,6 +376,8 @@ private Class<?> getReturnType(Method method) {
             Class<?> componentType = (Class<?>) ((GenericArrayType) returnTypeParameter).getGenericComponentType();
             // (issue #525) support List<byte[]>
             returnType = Array.newInstance(componentType, 0).getClass();
+          } else if (returnTypeParameter instanceof TypeVariable<?>) {
+            returnType = resolveTypeVariable(method, returnTypeParameter);
           }
         }
       }
@@ -605,4 +597,59 @@ private KeyGenerator handleSelectKeyAnnotation(SelectKey selectKeyAnnotation, St
     return answer;
   }
 
+  private Class<?> resolveTypeVariable(Method m, Type typeVariable) {
+      if (typeVariable instanceof  TypeVariable) {
+        Map<String, Type> genericTypes = parentTypeMap.get(m.getDeclaringClass().getName());
+        if (null != genericTypes) {
+          String genericTypeName = ((TypeVariable) typeVariable).getName();
+          Type returnClass = genericTypes.get(genericTypeName);
+          if (null != returnClass) {
+              return (Class<?>)returnClass;
+          }
+        }
+      }
+      return null;
+  }
+  private Class<?> resolveReturnType(Method m) {
+      Class<?> retClass = resolveTypeVariable(m, m.getGenericReturnType());
+      if (null != retClass) {
+        return retClass;
+      }
+      return m.getReturnType();
+  }
+
+  public void collectTypeParameters(Class<?> offspring, Type... actualArgs) {
+      assert offspring != null;
+
+      Map<String, Type> typeVariables = new HashMap<String, Type>();
+      for (int i = 0; i < actualArgs.length; i++) {
+          TypeVariable<?> typeVariable = (TypeVariable<?>) offspring.getTypeParameters()[i];
+          typeVariables.put(typeVariable.getName(), actualArgs[i]);
+      }
+      if (!typeVariables.isEmpty()) {
+        parentTypeMap.put(offspring.getName(), typeVariables);
+      }
+
+      // because offspring is a interface which only extends from other interface, it is no need
+      // get getGenericSuperClass
+      for (Type parent: offspring.getGenericInterfaces()) {
+          if (parent instanceof ParameterizedType) {
+              ParameterizedType parameterizedType = (ParameterizedType) parent;
+              Type rawType = parameterizedType.getRawType();
+              if (rawType instanceof Class<?>) {
+                  Class<?> rawTypeClass = (Class<?>) rawType;
+                  List<Type> resolvedTypes = new LinkedList<Type>();
+                  for (Type t : parameterizedType.getActualTypeArguments()) {
+                      if (t instanceof TypeVariable<?>) {
+                          Type resolvedType = typeVariables.get(((TypeVariable<?>) t).getName());
+                          resolvedTypes.add(resolvedType != null ? resolvedType : t);
+                      } else {
+                          resolvedTypes.add(t);
+                      }
+                  }
+                  collectTypeParameters(rawTypeClass, resolvedTypes.toArray(new Type[]{}));
+              }
+          }
+      }
+  }
 }

src/test/java/org/apache/ibatis/submitted/associationtest/AssociationTest.java

@@ -96,4 +96,22 @@ public void shouldGetAllCarsNonUnique() {
     }
   }
 
+  @Test
+  public void getSubGenericReturnType() {
+      SqlSession sqlSession = sqlSessionFactory.openSession();
+      try {
+          NoMapper mapper = sqlSession.getMapper(NoMapper.class);
+          Car car = mapper.getElement(1);
+          Assert.assertEquals(1, car.getId());
+
+          String carType = mapper.getMobileType("VW");
+          Assert.assertEquals("VW", carType);
+
+          List<String> carTypes = mapper.getAllCarTypes();
+          Assert.assertTrue(!carTypes.isEmpty());
+      } finally {
+          sqlSession.close();
+      }
+  }
+
 }

src/test/java/org/apache/ibatis/submitted/associationtest/AutomoblieMapper.java

@@ -0,0 +1,24 @@
+/**
+ *    Copyright 2009-2015 the original author or authors.
+ *
+ *    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.apache.ibatis.submitted.associationtest;
+
+import org.apache.ibatis.annotations.Param;
+import org.apache.ibatis.annotations.Select;
+
+public interface AutomoblieMapper<T> {
+    @Select("select cartype from cars where cartype=#{type}")
+    T getMobileType(@Param("type") String carType);
+}

src/test/java/org/apache/ibatis/submitted/associationtest/CarMapper.java

@@ -0,0 +1,19 @@
+/**
+ *    Copyright 2009-2015 the original author or authors.
+ *
+ *    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.apache.ibatis.submitted.associationtest;
+
+public interface CarMapper<E> extends GenericMapper<Car,E>, AutomoblieMapper<E> {
+}

src/test/java/org/apache/ibatis/submitted/associationtest/GenericMapper.java

@@ -0,0 +1,29 @@
+/**
+ *    Copyright 2009-2015 the original author or authors.
+ *
+ *    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.apache.ibatis.submitted.associationtest;
+
+import org.apache.ibatis.annotations.Param;
+import org.apache.ibatis.annotations.Select;
+
+import java.util.List;
+
+public interface GenericMapper<T, E> {
+    @Select("select carid as id, cartype as type from cars where carid=#{id}")
+    T getElement(@Param("id") int id);
+
+    @Select("select cartype from cars")
+    List<E> getAllCarTypes();
+}

src/test/java/org/apache/ibatis/submitted/associationtest/NoMapper.java

@@ -0,0 +1,24 @@
+/**
+ *    Copyright 2009-2015 the original author or authors.
+ *
+ *    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.apache.ibatis.submitted.associationtest;
+
+import org.apache.ibatis.annotations.Select;
+
+import java.util.List;
+
+public interface NoMapper extends CarMapper<String>{
+
+}

src/test/java/org/apache/ibatis/submitted/associationtest/mybatis-config.xml

@@ -35,6 +35,7 @@
 
 	<mappers>
 		<mapper resource="org/apache/ibatis/submitted/associationtest/Mapper.xml" />
+        <mapper class="org.apache.ibatis.submitted.associationtest.NoMapper"/>
 	</mappers>
 
 </configuration>