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Some Recipes to Improve Your Google Web Toolkit Development

Experiences, tips and techniques to assist you in creating GWT Web applications.

By Klaus P. Berg, JavaWorld.com, 04/26/07

Page 3 of 6

You can see the resulting directory structure for our example application in figure 1. If you look inside the JUnit2MR-client directory, you can see additional directories created during the deployment process, as well as an Eclipse launch configuration to start our GWT application "JUnit2MR" in hosted mode. My tip is to collect project-specific jar files in a directory called "lib", e.g., inside JUnit2MR-client/lib we have GWT add-on libraries like "gwt-tk" or "gwt-login". You can find a good list of third-party client-side GWT add-ons at the GWT Unofficial Wiki site (see Resources). The RPC-project does not need a lib directory in my case statudy, but the server-side project's lib directory will contain only jar files needed by your servlet code.

Using this three-projects GWT structure, the Eclipse launch configuration for your application in the GWT hosted mode is a little bit more complicated than having only one project. Therefore, I provide a screenshot in figure 2 that shows the necessary settings for my case study.

Figure 1: Eclipse project directory structure for client, rpc, and server-part

Figure 2: Eclipse launch configuration for GWT hosted mode

You can do even more on structuring your code by establishing a separate Java "rpc" package inside the client and rpc project. In the rpc project it will just replace the "client" package still containing your transfer objects and the asynchronous interface definitions. In the client project the "rpc" package must be added, and it will include your synchronous interface definitions (without the callback parameter) moved from the client packag e. The only thing left is to make the new rpc package known to GWT by adding the <source path="client"/><source path="rpc"/> statements to your GWT module description.

Tip 2: Debugging and Error Reporting: there is more than Window.alert ()

It's true: you can actually use your IDE's full debugging capabilities when creating GWT applications. But before digging into where the error may have occurred, you need solid exception reporting on both the client and the server side of your code. This is typically done with try/catch blocks. Inside a client-side catch block you should pay attention to the fact that the default method call e.printStackTrace() is not a suitable solution in all situations. It will work when running your application in GWT hosted mode, printing text to your Eclipse console. However, for web mode ask yourself: "Where will my stacktrace and error messages that I have sent to stdout or stderr be displayed?" One possible solution is to use Mat Gessel's debug utility classes (see Resources) but you need a browser JavaScript console to see the results in web mode.