Allow to override EndpointsMethodHandler creation in EndpointsServlet

- This allows full customization of response serialization, etc.

Author: Clément Denis

endpoints-framework/src/main/java/com/google/api/server/spi/EndpointsServlet.java

@@ -99,9 +99,7 @@ private PathDispatcher<EndpointsContext> createDispatcher() {
       MethodConfigMap methods = apiConfig.getApiClassConfig().getMethods();
       for (Entry<EndpointMethod, ApiMethodConfig> methodEntry : methods.entrySet()) {
         if (!methodEntry.getValue().isIgnored()) {
-          handlersBuilder.add(
-              new EndpointsMethodHandler(initParameters, getServletContext(), methodEntry.getKey(),
-                  apiConfig, methodEntry.getValue(), systemService));
+          handlersBuilder.add(createEndpointsMethodHandler(apiConfig, methodEntry));
         }
       }
     }
@@ -134,6 +132,12 @@ private SystemService createSystemService(ClassLoader classLoader,
     }
   }
 
+  protected EndpointsMethodHandler createEndpointsMethodHandler(ApiConfig apiConfig,
+      Entry<EndpointMethod, ApiMethodConfig> methodEntry) {
+    return new EndpointsMethodHandler(initParameters, getServletContext(), methodEntry.getKey(),
+        apiConfig, methodEntry.getValue(), systemService);
+  }
+
   /**
    * Creates a new instance of the specified service class.
    *