MigrateFromGWT

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To help us with migration there is a [[NetBeans]] module that can do this for us automatically.
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To help us with migration there is a [[NetBeans]] module that can do this for us automatically (either one by one or as a batch conversion).
 +
 
 +
=== Real [[HotSpot]] [[VM]] ===
 +
 
 +
When we have our libraries converted, we can use them in a ''knockout4j'' [[Maven]] archetype project and use it inside of [[JavaFX]] WebView. This gives us all the benefits of [[HotSpot]] and real [[Java]] (including features of modern [[JDK]]s).
 +
 
 +
We can use [[debugger]] and verify the behavior of the [[Java]] application logic the way we are used to.
 +
 
 +
=== [[Bck2Brwsr]] ===
 +
 
 +
Originally we started with a [[GWT]] application. Now we have real [[Java]] application, which can run on desktop and render its [[HTML]] UI via [[JavaFX]]. However our original application used to run in a browser? Can we do the same?
 +
 
 +
Yes, we can. With the help of [[Bck2Brwsr]] [[VM]], we can take the same application and repackage it so it runs in a pluginless browser. Just choose ''bck2brwsr'' [[Maven]] configuration and rebuild.
 +
 
 +
Enjoy your [[GWT]]-less [[HTML]]/[[Java]] applications!

Revision as of 18:23, 29 January 2014

GWT has a lot of drawbacks which Bck2Brwsr project addresses by allowing us to use real JVM. As such there is a value in migrating to this new system. Moreover the migration is quite easy. Let me give you a demo.

Contents

GWT Project

The primary focus right now is to show that the GWT Java to JavaScript native interface methods can easily be migrated to real HotSpot virtual machine. Imagine following application that talks directly to JavaScript in the browser: 

public class ButtonApp implements Runnable {
 
   public static void onLoad() {
        alert("Initializing...");
        html("<button id='x'>Click me!</button>");
        onClick("x", new Runnable() {
            public void run() {
                alert("Button was clicked!");
                later(new ButtonApp(), 1000);
            }
        });
    }
 
    public void run() {
        alert("One second after that!");
    }
 
  public static native void later(Runnable r, int time) /*-{
        window.setTimeout(function() {
            r.@java.lang.Runnable::run()();
        }, time);
    }-*/;
 
    public static native void html(String html) /*-{
        var b = document.getElementsByTagName("body")[0];
        b.innerHTML = html;
    }-*/;
 
    public static native void alert(String msg) /*-{
       alert(msg);
    }-*/;
 
    public static native void onClick(String id, Runnable r) /*-{
       document.getElementById(id).onclick = function() {
        r.@java.lang.Runnable::run()();
       };
    }-*/;
 
}

Of course, this is not typical GWT application. It does not use GWT widgets library. However the point to demonstrate is different: we want to see if we can convert the low level JSNI comments into something that can run on top of real JDK. Because if we can, reimplementing the widgets or other libraries is then just a bit of work.

Convert to Annotations

The first step is to convert comments into something that JVM can consume. Since JDK5 the proper way of attaching additional information to methods is to use annotations. Let's us rewrite the code to use @JavaScriptBody as provided by HTML4J library (see its javadoc). The goal is to have source like this: 

public class ButtonApp implements Runnable {                                                                                                                                                     
 
    public static void onLoad() {                                                                                                                                                            
        alert("Initializing...");                                                                                                                                                                
        html("<button id='x'>Click me!</button>");                                                                                                                                               
        onClick("x", new Runnable() {                                                                                                                                                            
            public void run() {                                                                                                                                                                  
                alert("Button was clicked!");                                                                                                                                                    
                later(new ButtonApp(), 1000);                                                                                                                                                    
            }                                                                                                                                                                                    
        });                                                                                                                                                                                      
    }                                                                                                                                                                                        
 
    public void run() {                                                                                                                                                                          
        alert("One second after that!");                                                                                                                                                         
    }                                                                                                                                                                                            
 
    @net.java.html.js.JavaScriptBody(args = {"r", "time"}, javacall = true, body = 
        "        window.setTimeout(function() {\n" +                                                                                                                                             
        "            r.@java.lang.Runnable::run()();\n" + 
        "        }, time);\n" + 
        "    ")
    public static native void later(Runnable r, int time);
 
    @net.java.html.js.JavaScriptBody(args = {"html"}, body =
        "        var b = document.getElementsByTagName(\"body\")[0];\n" + 
        "        b.innerHTML = html;\n" + 
        "    ")
    public static native void html(String html);
 
    @net.java.html.js.JavaScriptBody(args = {"msg"}, body =
        "       alert(msg);\n" + 
        "    ")
    public static native void alert(String msg);
 
    @net.java.html.js.JavaScriptBody(args = {"id", "r"}, javacall = true, body =        
        "       document.getElementById(id).onclick = function() {\n" + 
        "        r.@java.lang.Runnable::run()();\n" + 
        "       };\n" + 
        "    ")
    public static native void onClick(String id, Runnable r);
 
}

To help us with migration there is a NetBeans module that can do this for us automatically (either one by one or as a batch conversion).

Real HotSpot VM

When we have our libraries converted, we can use them in a knockout4j Maven archetype project and use it inside of JavaFX WebView. This gives us all the benefits of HotSpot and real Java (including features of modern JDKs).

We can use debugger and verify the behavior of the Java application logic the way we are used to.

Bck2Brwsr

Originally we started with a GWT application. Now we have real Java application, which can run on desktop and render its HTML UI via JavaFX. However our original application used to run in a browser? Can we do the same?

Yes, we can. With the help of Bck2Brwsr VM, we can take the same application and repackage it so it runs in a pluginless browser. Just choose bck2brwsr Maven configuration and rebuild.

Enjoy your GWT-less HTML/Java applications!

Retrieved from "http://wiki.apidesign.org/wiki/MigrateFromGWT"
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