Allow registering a type handler for a common interface of enums.

src/main/java/org/apache/ibatis/type/TypeHandlerRegistry.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2016 the original author or authors.
+ *    Copyright 2009-2017 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.
@@ -221,20 +221,32 @@ private Map<JdbcType, TypeHandler<?>> getJdbcHandlerMap(Type type) {
     }
     if (jdbcHandlerMap == null && type instanceof Class) {
       Class<?> clazz = (Class<?>) type;
-      jdbcHandlerMap = getJdbcHandlerMapForSuperclass(clazz);
-      if (jdbcHandlerMap != null) {
-        TYPE_HANDLER_MAP.put(type, jdbcHandlerMap);
-      } else if (clazz.isEnum()) {
-        register(clazz, new EnumTypeHandler(clazz));
-        return TYPE_HANDLER_MAP.get(clazz);
+      if (clazz.isEnum()) {
+        jdbcHandlerMap = getJdbcHandlerMapForEnumInterfaces(clazz);
+        if (jdbcHandlerMap == null) {
+          register(clazz, new EnumTypeHandler(clazz));
+          return TYPE_HANDLER_MAP.get(clazz);
+        }
+      } else {
+        jdbcHandlerMap = getJdbcHandlerMapForSuperclass(clazz);
       }
     }
-    if (jdbcHandlerMap == null) {
-      TYPE_HANDLER_MAP.put(type, NULL_TYPE_HANDLER_MAP);
-    }
+    TYPE_HANDLER_MAP.put(type, jdbcHandlerMap == null ? NULL_TYPE_HANDLER_MAP : jdbcHandlerMap);
     return jdbcHandlerMap;
   }
 
+  private Map<JdbcType, TypeHandler<?>> getJdbcHandlerMapForEnumInterfaces(Class<?> clazz) {
+    for (Class<?> iface : clazz.getInterfaces()) {
+      Map<JdbcType, TypeHandler<?>> jdbcHandlerMap = TYPE_HANDLER_MAP.get(iface);
+      if (jdbcHandlerMap != null) {
+        return jdbcHandlerMap;
+      } else {
+        return getJdbcHandlerMapForEnumInterfaces(iface);
+      }
+    }
+    return null;
+  }
+
   private Map<JdbcType, TypeHandler<?>> getJdbcHandlerMapForSuperclass(Class<?> clazz) {
     Class<?> superclass =  clazz.getSuperclass();
     if (superclass == null || Object.class.equals(superclass)) {

src/test/java/org/apache/ibatis/type/TypeHandlerRegistryTest.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2016 the original author or authors.
+ *    Copyright 2009-2017 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.
@@ -15,10 +15,7 @@
  */
 package org.apache.ibatis.type;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertSame;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 import java.net.URI;
 import java.sql.CallableStatement;
@@ -159,4 +156,40 @@ class MyDate2 extends MyDate1 {
     }
     assertEquals(DateTypeHandler.class, typeHandlerRegistry.getTypeHandler(MyDate2.class).getClass());
   }
+
+  interface SomeInterface {
+  }
+
+  enum SomeEnum implements SomeInterface {
+  }
+
+  class SomeClass implements SomeInterface {
+  }
+
+  @MappedTypes(SomeInterface.class)
+  public static class SomeInterfaceTypeHandler<E extends Enum<E> & SomeInterface> extends BaseTypeHandler<E> {
+    @Override
+    public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType)
+        throws SQLException {
+    }
+    @Override
+    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
+      return null;
+    }
+    @Override
+    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
+      return null;
+    }
+    @Override
+    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
+      return null;
+    }
+  }
+
+  @Test
+  public void demoTypeHandlerForSuperInterface() {
+    typeHandlerRegistry.register(SomeInterfaceTypeHandler.class);
+    assertNull("Registering interface works only for enums.", typeHandlerRegistry.getTypeHandler(SomeClass.class));
+    assertSame(SomeInterfaceTypeHandler.class, typeHandlerRegistry.getTypeHandler(SomeEnum.class).getClass());
+  }
 }