Question

Using DJ Native Swing it is possible to show a web page within a java application. When you do this it is also possible to communicate from the browser to the java runtime environment using the “command” protocol. The documentation has a code snippet which demonstrates it’s usage:

function sendCommand( command ){
    var s = 'command://' + encodeURIComponent( command );

    for( var i = 1; i < arguments.length; s+= '&' + encodeURIComponent( arguments[i++] ) );
      window.location = s;
}

As it looks here it seems to be a regular GET request to an url using the command protocol instead of http. Although when I create and image, script tag or just and ajax get request there is no response and the breakpoint in the java runtime isn’t triggered.

I don’t want to set the window.location because I don’t want to navigate away from the page I am currently at. Using the link to navigate to a command url does work though but it also navigates away from the current page. The page uses OpenLayers and dojo. (I have also tried dojo.io.script)

Answer 1

After some work I have found a neat way to communicate with the java runtime which doesn’t trigger a refresh of the page every time there is communication. It is inspired on the way JSONP works to get around the cross domain restriction in most browsers these days. Because an iFrame will also trigger a command:// url it possible to do a JSONP like action using this technique. The code on the client side (browser):

dojo.provide( "nmpo.io.java" );
dojo.require( "dojo.io.script" );

nmpo.io.java = dojo.delegate( dojo.io.script, { 
    attach: function(/*String*/id, /*String*/url, /*Document?*/frameDocument){
        //  summary:
        //      creates a new  tag pointing to the specified URL and
        //      adds it to the document.
        //  description:
        //      Attaches the script element to the DOM.  Use this method if you
        //      just want to attach a script to the DOM and do not care when or
        //      if it loads.        
        var frame = dojo.create( "iframe", { 
            id: id,
            frameborder:  0,
            framespacing: 0
        }, dojo.body( ) );

        dojo.style( frame, { display: "none" } );
        dojo.attr( frame, { src: url } );
        return frame;
    },

    _makeScriptDeferred: function(/*Object*/args){
        //summary: 
        //      sets up a Deferred object for an IO request.
        var dfd = dojo._ioSetArgs(args, this._deferredCancel, this._deferredOk, this._deferredError);

        var ioArgs = dfd.ioArgs;
        ioArgs.id = dojo._scopeName + "IoScript" + (this._counter++);
        ioArgs.canDelete = false;

        //Special setup for jsonp case
        ioArgs.jsonp = args.callbackParamName || args.jsonp;

        if(ioArgs.jsonp){
            //Add the jsonp parameter.
            ioArgs.query = ioArgs.query || "";
            if(ioArgs.query.length > 0){
                ioArgs.query += "&";
            }
            ioArgs.query += ioArgs.jsonp
                + "="
                + (args.frameDoc ? "parent." : "")
                + "nmpo.io.java.jsonp_" + ioArgs.id + "._jsonpCallback";

            ioArgs.frameDoc = args.frameDoc;

            //Setup the Deferred to have the jsonp callback.
            ioArgs.canDelete = true;
            dfd._jsonpCallback = this._jsonpCallback;
            this["jsonp_" + ioArgs.id] = dfd;
        }
        return dfd; // dojo.Deferred
    }
});

When a request is sent to the java runtime a callback argument will be supplied and a webBrowser.executeJavascript( callbackName + "(" + json + ");" ); action can be executed to trigger the callback in the browser.

Usage example client:

dojo.require( "nmpo.io.java" );
nmpo.io.java.get({
    // For some reason the first paramater (the one after the '?') is never in the
    // paramater array in the java runtime. As a work around we stick in a dummy.
    url: "command://sum?_",
    callbackParamName: "callback",
    content: {
        numbers: [ 1, 2, 3, 4, 5 ].join( "," )
    },
    load: function( result ){
        console.log( "A result was returned, the sum was [ " + result.result + " ]" );  
    }   
});

Usage example java:

webBrowser.addWebBrowserListener(new WebBrowserAdapter() {
    @Override
    public void commandReceived(WebBrowserCommandEvent e) {
        // Check if you have the right command here, left out for the example
        // Parse the paramaters into a Hashtable or something, also left out for the example
        int sum = 0;
        for( String number : arguments.get( "numbers" ).split( "," ) ){
            sum += Integer.parseInt( number );
        }

        // Execute the javascript callback like would happen with a regular JSONP call.
        webBrowser.executeJavascript( arguments.get( "callback" ) + "({ result: " + sum + " });" );
    }
});

Also with IE in the frame I can highly recommend using firebug lite, the dev tools for IE are not available.