To create a webstart application you need to create a JNLP descriptor. See http://docs.oracle.com/javase/1.5.0/docs/guide/javaws/developersguide/syntax.html for the syntax.
The codebase specifies the location where java can find your files (all resources in the jnlp file are relative to this path). When you deploy your Web Start application, this will be the location on the http server where you upload your application (eg: http://www.mysite.com/myapp).
When you're developing or testing your application, you don't want to upload it every time you make a change. Unfortunately, you can't leave the codebase blank. Leaving it blank will give you the following exception:
The field <jnlp>href has and invalid value:
So what should you put there? You can't put the path to your application (eg: c:/myapp), since that will leave you with the same error message.
Your next try might be file:///c:/myapp or file:/c:/myapp, which won't work either. The correct syntax is:
file://localhost/C:/myapp
Now you can test your Web Start application locally!
