The problem: I want to expose application back end functionality on Google Application Engine (GAE) to the GWT and Java SE front ends in the same way. I did not want to code 2 different technology things that do same business logic.

The Discussion: all 3 playing technologies use Java... GWT standard way to talk to server is GWT RPC - works great. But Zipped JSON underneath (seen somewhere analysis of the traffic done with a proxy.)

For Java Web Start App written with Java SE 6 any kind of serialization is an option but the rest of the protocol can be tricky to code test and maintain.

Easy to see that what I was looking was a way to create some kind of web services on GAE, but the classic Web Services with AXIS does not work (this is by design, documented and understandable).

So everyone I asked offered me to code a bunch of servlets to return XML serialization of the same POJOs used in GWT RPS realization. But I was looking for a way to have more than a single servlet for a single RPC method hand coded. So run in to the restlet.org And U know what?! It worked just out of the box.

The Solution:
The recipe is like that:

Get from restlet.org the restlet-gae-2.0m4.zip this is a GAE edition of the 2nd version that currently in development but as they work fast and release often - it will be production ready before I even start testing anything real.

Create a GAE web app in Eclipse 3.5 with Google Plugin.

Add 2 jars: org.restlet.ext.servlet.jar org.restlet.jar to the \war\WEB-INF\lib\ and to the build path of the project

create classes:

package biz.daich.google.engine.ex1.code.server.restlets;

import org.restlet.resource.Get;

import org.restlet.resource.ServerResource;

public class HelloWorldResource extends ServerResource {

@Get

public String represent() {

return "hello, world (from the cloud!)";

}

}

-------------------------------------------

package biz.daich.google.engine.ex1.code.server.restlets;

import org.restlet.Application;

import org.restlet.Restlet;

import org.restlet.routing.Router;

public class RestletsApplication extends Application {

/**

* Creates a root Restlet that will receive all incoming calls.

*/

@Override

public synchronized Restlet createRoot() {

// Create a router Restlet that routes each call to a

// new instance of HelloWorldResource.

Router router = new Router(getContext());

// Defines only one route

router.attach("/", HelloWorldResource.class);

return router;

}

}

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\war\WEB-INF\web.xml should look like this :

Pei_pivo.html

org.restlet.application

biz.daich.google.engine.ex1.code.server.restlets.RestletsApplication

RestletServlet

org.restlet.ext.servlet.ServerServlet

RestletServlet

/restlets/*

===============================================

now in the debug mode it works OK when you go to the http://localhost:8080/restlets/

it shows "hello, world (from the cloud!)" as expected.

see restlet.org wiki and documentation. It has GWT connector too. Will try it next.