Java - JavaScript Communication example

mbien — Tue, 12 May 2009 16:22:57 +0000

Communication between java applets and javascript code is already available since J2SE 1.3 (aka LiveConnect, which was btw. rewritten from scratch in Java 6 update 10 as part of the new plugin) and is really easy to implement. It is a simple way to break out of the sandbox and do things which would usually require full system access (a signed applet + user approval via security dialog). For example applets living in a sandbox are only allowed to read mouse events via the AWT/Swing event mechanism which works as long the mouse is over the applet.

To read e.g the mouse position globaly you would need to call MouseInfo.getPointerInfo().getLocation() which would cause a java.security.AccessControlException: access denied. However, in javascript it is trivial to track mouse events for the whole html document (e.g google adds track onclick x,y events).

All you have to do is to use the object tag instead of applet tag (which is deprecated anyway) and give the object (applet) a name via the id attribute.

<form name="FishForm">   
    <object width="256" height="256" type="application/x-java-applet" id="CrazyFish">
        <param value="http://people.fh-landshut.de/~mbien/weblog/java_js_interop/launch.jnlp" name="jnlp_href" />
        <param value="false" name="draggable" />
    </object>
</form>

now you can simply call methods as usual.

<script language="JavaScript1.2">
     //...
     document.onmousemove = onMouseMoved;

     var tempX = 0;
     var tempY = 0;

     var applet = document.FishForm.CrazyFish;

     function onMouseMoved(e) {
         //...
         // javascript -> java calls
         applet.jsObjectOrigin(findPosX(applet), findPosY(applet));
         applet.jsMouseMoved(tempX, tempY)
         return true
     }
     //...
 </script>

the other side is a plain old public method implemented in the java applet.

    /**
     * called from javascript.
     */
    public void jsMouseMoved(int x, int y) {
        //do something usefull
    }

RIA/Web2.0 Observer Pattern in action ;)

(The applet won't work with JRE version < 1.6 update 10 (or the equivalent on Mac OS) since I used the jnlp deployment mechanism, but it wouldn't have been necessary for this particular applet)

... and never forget Web 2.0 is watching you

NetBeans 7.0 with better desktop integration planed

mbien — Tue, 1 Apr 2008 11:42:54 +0000

Note: This entry has been posted on 1. April 2008 and nothing of that below is true :-)

- - - - -

You probably already know a lot of changes are planed for the NetBeans 7.0 release.

One of the bigger changes is tighter integration to the Windows Presentation Foundation for the SWT/JFace rewrite of NetBeans 7.0 similar tho the Eclipse roadmap. The minimum system requirement will rise to windows vista ultimate with a DirectX 10 capable graphics card and a USB stick plugged into your system (swap file for java quickstarter) to render NetBeans 7 in full HD. The primary reason for that was the out of the box Java 6 incompatibility to apple systems (who knows maybe it is compatible with MacOS X but no one will tell you because if he tried installing SE 6 on macs he/she also signed an NDA...) and the issue that many architects simple do not understand the internals of linux distributions (e.g Ubuntu) to install NetBeans.

On older cards or other operating systems JEdit will be started in compatibility mode (motif look&feel and full shell support). The reason for that are the new consumer guidelines and download size limitations of the java 6 Update 10 release. (there is a because of backwards compatibility problems [to build 11] not fixable ArrayIndexOutOfBounds bug in the pack200 implementation - primary reason why the swing renderer does not fit into the NB 7 distribution anymore if started with Java 6 update 10).

This brings several advantages. E.g instead of playing Jake in the browser (update 10 required) NetBeans 7.0 will be capable to render Halo 3 in the editor pane (with full profiler integration and 16x FSAA text overlay). Regular patches will be available via update center.

Additionally to that better joystick support is planed. This should improve the navigation through larger projects and replace the "go to declaration" action. You may also activate the force feedback option in the new "user experience" tab in the options dialog to detect the files which causes unit tests to fail. (Note: not available in JEdit compatibility mode but there will be a blinking icon instead)

The higher costs to develop NetBeans 7.0 make a complete free distribution not feasible but it will be still free for opensource developers (but not without limitations e.g UML diagrams will be limited to only two kind of widgets "hack" and "ship" while maintaining 100% SSP compatibility).

Michael Bien's Weblog

Java - JavaScript Communication example

NetBeans 7.0 with better desktop integration planed