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Level: Intermediate

Philip McCarthy ([email protected]), Software development consultant, Independent

08 Nov 2005

Exciting as it is, adding Ajax functionality to your applications can mean a lot of hard work. In this third article in the Ajax for Java developers series, Philip McCarthy shows you how to use Direct Web Remoting (DWR) to expose JavaBeans methods directly to your JavaScript code and automate the heavy-lifting of Ajax.

Understanding the fundamentals of Ajax programming is essential, but if you're building complex Ajax UIs, it's also important to be able to work at a higher level of abstraction. In this third article in the Ajax for Java developers series, I build on last month's introduction to data serialization techniques for Ajax, introducing a technique that will let you avoid the nitty-gritty details of serializing Java objects.

In the previous article, I showed you how to use JavaScript Object Notation (JSON) to serialize data in a format easily converted into JavaScript objects on the client. With this setup, you can invoke remote service calls using JavaScript code and receive JavaScript object graphs in response, not unlike making a remote procedure call. This time, you learn how to take things one step further, using a framework that formalizes your ability to make remote procedure calls on server-side Java objects from JavaScript client code.

DWR is an open source, Apache licensed solution consisting of server-side Java libraries, a DWR servlet, and JavaScript libraries. While DWR is not the only Ajax-RPC toolkit available for the Java platform, it is one of the most mature, and it offers a great deal of useful functionality. See Resources to download DWR before proceeding with the examples.

What is DWR?

In the simplest terms, DWR is an engine that exposes methods of server-side Java objects to JavaScript code. Effectively, with DWR, you can eliminate all of the machinery of the Ajax request-response cycle from your application code. This means your client-side code never has to deal with an XMLHttpRequest object directly, or with the server's response. You don't need to write object serialization code or use third-party tools to turn your objects into XML. You don't even need to write servlet code to mediate Ajax requests into calls on your Java domain objects.

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