Testing on an HTTP Preview server
Use the HTTP Preview server when you want to quickly test resources in a static Web project. The HTTP Preview server is a Hypertext Transfer Protocol (HTTP) embedded test server that is integrated with the workbench. It is intended for preliminary testing and saves you time to download, install, and set up an HTTP server. However, as your static Web project progresses through its development cycle you are encourage to test and run on an external HTTP server. You can use the HTTP Preview server as a convenient way to check for errors before you do a final test on an external HTTP server.
Testing on a J2EE Preview server
Use the J2EE Preview server when you want to quickly compile, test and run resources in a J2EE Web project. The J2EE Web projects you can test on a J2EE Preview server are static Web projects, dynamic Web projects and utility projects. Hereafter, the term J2EE Web project refers to any of these previously mentioned projects.