Java Stammtisch Carol McDonald

This Sample Slideshow app demonstrates the usage of the dojo Ajax framework, Comet, Bayeux, with Grizzly and Glassfish.

Download the dojo Comet Sample Application Code

dojo is an open source DHTML toolkit written in JavaScript. It includes many utilities that go beyond Ajax, for example the dojox.comet module simplifies programming comet applications. Comet is a term coined by Alex Russell  to describe applications where the Server pushes data to the client.  For example in the diagram below on the left you see  Ajax polling which uses synchronous requests/responses to get events from the server. Comet  uses long-lived previously-opened HTTP connections to "push" data to the client at any time, not only in response to user input.


Grizzly is an HTTP framework which uses the Java™ NIO API to provide fast HTTP processing . Grizzly provides Comet (long-lived streaming HTTP connections) support built on top of Grizzly's Asynchronous Request Processing (ARP).  With Grizzly ARP,  each Comet request isn't holding onto a thread which gives scalability.   Bayeux is a protocol for routing JSON encoded events between clients and servers in a publish subscribe model.  Grizzly provides an implementation of Bayeux, which makes it really easy to build Comet applications with dojo, you just configure Glassfish for Comet and configure your Web Application's web.xml for the Grizzly  Bayeux servlet  then you can use the dojox cometd publish and subscribe methods to send and receive Comet events as described in more detail below. 




Grizzly comes with Glassfish , or it can be used separately. To use Comet with Glassfish you just need to add the bold red line to the Glassfish config  domain.xml:

<http-listener acceptor-threads="1" address="0.0.0.0" 
  blocking-enabled="false" default-virtual-server="server" 
  enabled="true" family="inet" id="http-listener-1" port="8080" 
  security-enabled="false" server-name="" xpowered-by="true">
   <property name="cometSupport" value="true"/>
</http-listener>

to enable Bayeux on Glassfish, add the following to your Web application web.xml :

<servlet>
   <servlet-name>Grizzly Cometd Servlet</servlet-name>
   <servlet-class>
	com.sun.grizzly.cometd.servlet.CometdServlet
   </servlet-class>
   <init-param>
      <description>
	expirationDelay is the long delay before a request is
	resumed. -1 means never.
      </description>
      <param-name>expirationDelay</param-name>
      <param-value>-1</param-value>
   </init-param>
   <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
   <servlet-name>Grizzly Cometd Servlet</servlet-name>
   <url-pattern>/cometd/*</url-pattern>
</servlet-mapping>	

Package your war and deploy it on Glassfish,  then every request sent to your war's context-path/cometd/ will be serviced by the Grizzly Bayeux runtime.

Explanation of the usage of dojox cometd in the sample Slideshow Application

Quick installation and use of dojo with Netbeans

Loading base dojo and required modules into an application

Initializing a connection between the dojo client and the Grizzly BayeuxServlet

Publishing the next slide for the Comet Slideshow

Running the Sample Code

The sample code  is available as a NetBeans project. You can build and run the sample code using the NetBeans IDE.

Setting Things Up

• Download and install NetBeans 6.1 bundled with GlassFish V2
  
• Alternatively you can  Download and install GlassFish V2 separately.
• To use Comet with Glassfish you just need to add the bold red line to the Glassfish config  domain.xml (in the directory glassfish/domains/domain1/config ):

  Code Sample from:  index.html

  <http-listener acceptor-threads="1" address="0.0.0.0" blocking-enabled="false" default-virtual-server="server" enabled="true" family="inet" id="http-listener-1" port="8080" security-enabled="false" server-name="" xpowered-by="true"> <property name="cometSupport" value="true"/> </http-listener>

• Bayeux and dojo are already configured in the sample code.
  

Open and Run the Sample code:

1. Download the sample code and extract its contents. You should now see the newly extracted directory as <sample_install_dir>/dojoComet, where <sample_install_dir> is the directory where you unzipped the sample package. For example, if you extracted the contents to C:\ on a Windows machine, then your newly created directory should be at C:\dojoComet.
   
   
2. Start the NetBeans IDE. Click Open Project in the File menu and select the dojoComet directory you just unzipped.
   
   
3. Build the project as follows:
   
   
   • Right click the dojoComet node in the Projects window.
     
   • Select Clean and Build Project.
     
     
4. Run the project as follows:
   
   
   • Right click the dojoComet node in the Projects window.
     
   • Select Run Project.
     

When you run the project, your browser should display the opening page of the Sample Application (at http://localhost:8080/dojoComet/). Open another browser and set that url to http://localhost:8080/dojoComet/  then enter a name and click on the join button in both browser windows.   Then click on the next slide button in one browser window.  Both browsers should get updated with the next slide.  

For more Information:

• Jean-Francois Arcand's Blog on Cometd framework and its Bayeux protocol support in Grizzly
• Using the Grizzly Comet API
  
• dojo toolkit
  
• dojo cometd
  
• grizzly
• glassfish
• Enterprise Comet: Awaken the Grizzly!
• Asynchronous HTTP and Comet architectures
• A Comparison of Push vs Pull Ajax
• Comet and Reverse Ajax: The Next Generation Ajax 2.0 book