SimpleGWTWebWorker

A simple example of a WebWorker coded using the Google Web Toolkit

It uses the gwt-webworker library, from Manfred Tremmel which in turn has been taken from Google speedtracer.

The Worker (org.singsurf.simplewebworker.worker.SimpleWorker) is simply:

public class SimpleWorker extends DedicatedWorkerEntryPoint 
        implements MessageHandler {

   @Override
   public void onWorkerLoad() {
       setOnMessage(this);
   }

    @Override
    public void onMessage(MessageEvent event) {
	    String str = event.getDataAsString();
	    StringBuilder sb = new StringBuilder();
	    for(int i=str.length()-1;i>=0;--i) {
	        sb.append(str.charAt(i));
	    }
	    String res = sb.toString();		
	    postMessage(res);
    }
}

and the client (org.singsurf.simplewebworker.client.SimpleClient) is:

public class SimpleClient implements EntryPoint {

	@Override
	public void onModuleLoad() {

		final TextBox nameField = new TextBox();
		nameField.setText("Test input");
		final Label errorLabel = new Label();
		errorLabel.setText("");

		final Worker worker = Worker.create("worker/worker.nocache.js");
		
		final MessageHandler webWorkerMessageHandler = new MessageHandler() {
			@Override
			public final void onMessage(final MessageEvent pEvent) {
				nameField.setText(pEvent.getDataAsString());
			}
		};

		final ErrorHandler webWorkerErrorHandler = new ErrorHandler() {
			@Override
			public void onError(final ErrorEvent pEvent) {
				errorLabel.setText(pEvent.getMessage());
			}
		};

		worker.setOnMessage(webWorkerMessageHandler);
		worker.setOnError(webWorkerErrorHandler);


		final Button sendButton = new Button("Reverse!", new ClickHandler() {
			public void onClick(ClickEvent event) {
				worker.postMessage(nameField.getText());
			}
		});

		RootPanel.get("nameFieldContainer").add(nameField);
		RootPanel.get("sendButtonContainer").add(sendButton);
		RootPanel.get("errorLabelContainer").add(errorLabel);
	}
}

The worker code needs to be compiles as a separate GWT module using the "dedicatedworker" linker which adds some necessary javascript to the code. The client code can be compiled in as a normal module which also inherits the com.google.gwt.webworker.WebWorker module. It all needs to be compiled in production mode, trying to use dev-mode will result in a error about the DedicatedWorkerLinker. The maven configuration has not been set up to allow compilation.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.8.1//EN"
  "http://gwtproject.org/doctype/2.8.1/gwt-module.dtd">

<module rename-to='worker'>
	<inherits name='com.google.gwt.core.Core'/>
	<inherits name="com.google.gwt.http.HTTP" />  
	<inherits name='com.google.gwt.webworker.WebWorker' />

	<set-property name="user.agent" value="safari" />
	<set-configuration-property name="user.agent.runtimeWarning" value="false" />

	<!-- Use the WebWorker linker for a Dedicated worker -->
	<add-linker name="dedicatedworker" />

	<!-- Specify the app entry point classes.                         -->
  	<entry-point class='org.singsurf.simplewebworker.worker.SimpleWorker'/>
    <source path='worker' />
</module>

A sample webpage can be found in the war directory.

Serialisation using AutoBeans

A second version of the client and worker uses AutoBeans. Here factory methods can be used to create beans with a given set of getter and setter methods. These beans can then be easily serialised and deserialised to send receive data from the web worker. There are three packages for this method

• org.singsurf.simplewebworker.common contains methods to create beans and serialised and deserialised them
• org.singsurf.simplewebworker.beanclient contains the BeanClient class
• org.singsurf.simplewebworker.beanworker contains the BeanWorker class.

The sample webpage is in the war directory.

Note that the AutoBean code only works with beans created by the factories using interfaces. The can not be used concrete classes implementing the interfaces.

Example web pages using these two mechanisms can be found at SimpleWebWorker and BeanWorker.