I developed a web application (works properly) which registers a user to the system and allows user to upload a file to system via https. The client side code is totally developed by using GWT 2.4 and the back end is several servlets. Except the upload code, all the client-server communications are done via using ServiceAsync interface as it is the common practice in GWT. The upload code is based on a form which is communicating with the upload servlet directly.
This project is developed as a course work and my Professor is keen on knowing the underlying architecture of google web toolkit specificly focused on the client-server communication. His question was,
“How the client code knows the server’s url so that all the communication is done?”
His question is legitimate for the ServiceAsync interface. I am calling a function on the server side which seems interesting to him and he wants to know the underlying process behind it.
For uploading, I just defined uploadForm.setAction(GWT.getModuleBaseURL()+"upload"); where upload is the name of the upload servlet in web.xml.
I told him that the compiler generates Javascript code which contains all the web application code (whole system developed dynamically) and the url to the servlet is placed in that script file however the answer did not satisfy him. Please let me know the inner facts of the client-server communication with GWT.
Please give me some answers that can help my Professor to understand GWT’s asynchronous client-to-server RPC communication.
The underlying technology is shown here as a diagram. Google says “GWT provides an RPC mechanism based on Java Servlets to provide access to server side resources. This mechanism includes generation of efficient client and server side code to serialize objects across the network using deferred binding.”
The client knows the URL to query because you would have annotated your service interface with a
@RemoteServiceRelativePathtag. This associates the service with a default path relative to the module base URL. That URL is where Javascript sends your request.There’s a lot more to learn about GWT’s RPC if you care to, and you can start picking it apart here and here.