This chapter presents the Restlet edition for GWT, which is a client-side port of the Restlet Framework to GWT 2.2 and above releases.


Google Web Toolkit is a powerful and widely used platform for rich internet application. It is based on a smart compiler taking Java source and producing optimized JavaScript (byte)code.

By default, GWT recommends using a custom GWT-RPC mechanism to communicate between the GWT front-end (Web browser) and the back-end (Web server). In addition, the back-end has to be built using a Servlet container in order to work properly and to invoke your custom classes and methods. This might remind you of the RMI (Remote Method Invocation) or CORBA mechanisms and it comes with the same issues: the tight coupling between client and server code. Also, this reduces the opportunities of integration with other back-end technologies, outside Java/Servlet.

As you know, REST is a much more flexible and interoperable way to communicate between a client and a server. On the server-side, you can use Restlet or alternative technologies. But on the GWT front-end, the support has been limited so far. The GWT API does contain classes to send HTTP requests but they are quite low-level (you need to understand the HTTP headers syntax for example) and slow down productivity.

With the GWT 1.5 release and its support for the Java 5 syntax, it became possible to automate the port of the Restlet Framework to GWT. Of course, we kept only the classes required for the client-side obviously and had to remove classes based on Java APIs not available in GWT (such as NIO channels or BIO streams).

Automatic bean serialization

Finally, Restlet 2.0 added support for annotated Restlet interfaces and automatic bean serialization into its GWT edition, in a way that is consistent with other editions. See this first application example. With this feature, you don’t need to care about formatting or parsing your beans in JSON or XML as the Restlet edition for GWT with automatically generate serializer classes for you using GWT Deferred Binding mechanism and reusing the bean serialization format of GWT-RPC (not the protocol, just the format). Combined with easy content negotiation on the Restlet server-side, your web API stays unchanged, able to support JSON, XML and other formats in parallel with no code change!