Java to JavaScript using GWT compiler

Question

I have some Java code written that I\'d like to convert to JavaScript. I wonder if it is possible to use the GWT compiler to compile the mentioned Java code into JavaScript code

Answer 1

Although you can set the compiler to output 'pretty' code, I suggest you write export functions for the classes you want to call from outside your GWT project. I believe somewhere in the GWT documentation it's detailed how to do this, but I couldn't find it so here an example I just created.

class YourClass {
    public YourClass() {
        ...
    }

    public void yourMethod() {
        ...
    }

    public static YourClass create() {
        return new YourClass();
    }

    public final static native void export() /*-{
          $wnd.YourClass = function() {
              this.instance = new @your.package.name.YourClass::create()()
          }

          var _ = $wnd.YourClass.prototype;
          _.yourMethod = function() {this.instance.@your.package.name.YourClass::yourMethod()()}
    }-*/;
}

EDIT

To elaborate, your code will get obfuscated like normal, but thanks to the export function, you can easily reference those functions externally. You don't have to rewrite anything from your Java class in JavaScript. You only write the references in JavaScript, so you can do this:

var myInstance = new YourClass();
myInstance.yourMethod();

Of course you have to call the static export method from somewhere in your GWT app (most likely in your EntryPoint) to make this work.

More info about referencing Java methods from JavaScript: http://code.google.com/webtoolkit/doc/latest/DevGuideCodingBasicsJSNI.html#methods-fields

Answer 2

Maybe I can answer your second question: "If GWT compiler can't do this, can some other tool?"

I am using Java2Script for quite a while now, also on quite large projects. Integration with native JavaScript is fine, names are preserved, and after some time one can even match the generated JavaScript (in the browser debugger) with the original Java code with little effort.

Udo

Answer 3

You can "export" your function by writing inline JavaScript that calls it, and there is a tool gwt-exporter that does this automatically when you annotate classes and methods with @Export and similar. More information: https://code.google.com/p/gwtchismes/wiki/Tutorial_ExportingGwtLibrariesToJavascript_en

Answer 4

No - this isn't possible with the GWT compiler, since the GWT compiler is build to generate optimized and very performant JavaScript out of Java.

The big advantage is, that you can maintain your projekt in Java and compile it with GWT to JavaScript. So there is no need to prevent the variable-names and method-names in the JavaScript result, since all changes and work is done in the JAVA-sources.

Working in the JavaScript-output of GWT just isn't that easy and is really a lot of work!

Update:

By a hint of David, I found the Compiler-Option "-style". You can have a try with the following options:

-style=PRETTY -optimize=0

I have no idea if this will really generate "human readable" code. I think it won't, since the GWT framework will still be part of the resulting JavaScript and so it will be difficult to make changes to the JavaScript-result. Have a try and let us know ...