Wicket Native WebSockets

What ?

Since version 6.0 Wicket provides an experimental module that provides integration with WebSocket support in the web containers like Jetty and Tomcat.

How it works ?

Each of the integrations provide a custom implementation of org.apache.wicket.protocol.http.WicketFilter that first checks whether the current web request needs to upgrade its protocol from HTTP to WebSocket. This is done by checking the request headers for the special header with name "Upgrade". If the request is an upgrade then the filter registers an endpoint for the web socket connection. Later this endpoint is used to read/write messages from/to the client.
All messages sent through the web socket connection are not intercepted by WicketFilter. This is how the web containers currently work.
When a client is connected it is being registered in a global (application scoped) registry using as a key the application, the client session and the id of the page that registered it. Later when the server needs to push a message it uses this registry to filter which clients need to receive the message.
When a message is received from the client Wicket uses the associated page id for the web connection and loads the Wicket Page as Ajax requests do, then it broadcasts a IWebSocketMessage (Wicket 1.5 Event system) to all its components so they can react on it.
The server-side can push plain text and binary messages to the client - pure web socket messages, but can also add components for re-render, prepend/append _javascript_ as you do with AjaxRequestTarget.

How to use it ?

Add org.apache.wicket.protocol.ws.api.WebSocketBehavior to the page that will use web socket communication:

MyPage.java

public class MyPage extends WebPage {


  public MyPage()
  {
    add(new WebSocketBehavior() {
      @Override
      protected void onMessage(WebSocketRequestHandler handler, TextMessage message)
      {
      }
    });
  }
}

Use message.getText() to read the message sent by the client and use the passed handler.push(String) to push a text message to the connected client. Additionally you can use handler.add(Component...) to add Wicket components for re-render, handler#prependJavaScript(CharSequence) and handler#appendJavaScript(CharSequence) as you do with AjaxRequestTarget.

Differences with Wicket-Atmosphere module.

Wicket-Atmosphere provides integration with Atmosphere and let it handle the inconsistencies in WebSocket protocol support in different browsers and web containers. If either the browser or the web container do not support WebSockets then Atmosphere will downgrade (depending on the configuration) to either long-polling, streaming, server-side events, jsonp, ... to simulate the long running connection.

Wicket Native WebSocket uses only WebSocket connections, so it wont work for browsers and web containers which do not support WebSockets. There are no plans to add such support in future. Use it only if you really know that you will run your application in an environment that supports WebSockets.

Currently supported web containers are Jetty 7.5+ and Tomcat 7.0.27+.
Currently supported browsers are Google Chrome/Chromium, Firefox 11+, Safari 5.x (with Jetty), IE10.

Change Notification Preferences

View Online | Add Comment

[CONF] Apache Wicket > Wicket Native WebSockets