Generic GUI embeddable in a jar?

Writing a GUI for a library/tool is quite common and each time the question how do I do or package it leads to a headache.

You can use any existing web framework but you risk a conflict with the application. So basically the solution is to use client side technology or a jsp/servlet.

So how to do so? First you need a servlet 3.0 server (or any JavaEE 6 server). It basically means it works in Tomcat, TomEE, Glassfish, JBoss…

Then you need to know you can put resources in META-INF/resources as if it was in your webapp directly in root folder (= accessible from the web) – I discovered it recently on Alexis MP blog.

Then in my case I didn’t want a full client side development since it was bringing back too much js dependencies and a JAXRS server to be clean…but the GUI was very light so I simply used a controller (a servlet) and few views (JSPs) that I put in META-INF/resources.

At this point my views are accessible but since my controller is not bound it is quite useless.

To bind it automatically Servlet 3.0 specification brings you javax.servlet.ServletContainerInitializer. Implementing it you get a hook called at startup and thanks to javax.servlet.ServletContext you can add your servlet. Here is my implementation:

public class MyServletInitializer implements ServletContainerInitializer {
    @Override
    public void onStartup(final Set<Class<?>> classes, final ServletContext ctx) throws ServletException {
        ctx.addServlet("My Controller", new MyController()).addMapping("/demo/*");
    }
}

And that’s all! Now i add my jar to any WEB-INF/lib and the gui is accessible :). Awesome for admin GUIs!

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