GWT RequestBuilder vs RPC vs Script-Include

Which should we use: GWT RPC or RequestBuilder?

GWT presents four ways to perform async data transfer with the server.

• GWT RPC
• RequestBuilder
• javascript include
• the new-fangled ORM-friendly RequestFactory/EventBus

GWT RPC is built on XMLHttpRequest (look up wikipedia on that) and therefore suffers the restriction of SLD SOP (Second level domain Same origin policy). I wrote a description of this at http://h2g2java.blessedgeek.com/2009/08/gwt-rpc.html. No doubt, newer browsers including IE 8 have a non-w3c-sanctioned XDomainRequest but I doubt GWT RPC has acquiesced to that new development.

RequestBuilder is also built on XMLHttpRequest. The difference between the two is that GWT RPC is an elaborate framework to define the client-server communication channel utilizing interfaces to provide Serializable POJO (plain old Java objects) transfer of data. Whereas RequestBuilder is simpler and more palatable to the usual adhoc-quick-and-dirty programmer. RequestBuilder requires you to concoct your own object data structure marshalling/demarshalling because you have to pass your data as String. But then you could encode the data structures using GWT's JSON marshalling/demarshalling routines. You can find my routine in Google Code to perform JSON data-transfer at http://code.google.com/p/synthfuljava/source/browse/trunk/gwt/http/org/synthful/gwt/http/client/JsonHttpResponseHandler.java

Is it true that GWT RPC actually calls RequestBuilder? I need to pace through the debugger to confirm that. I think I have already done that sometime before that confirms that GWT RPC actually calls RequestBuilder. In fact, GWT RPC converts your POJOs into JSON behind your back.

To circumvent the SLD SOP restriction, whether in Javascript or any means of AJAX, you have to use the Javascript script include technique. i.e., < SCRIPT SRC='...' > tag. Without further explanation, you could read my code on how to do that in the class JsonRemoteScriptCall at http://code.google.com/p/synthfuljava/source/browse/trunk/gwt/jsElements/org/synthful/gwt/javascript/client/JsonRemoteScriptCall.java.

OK, I shall leave the more complex RequestFactory/EventBus technique for another posting.