If an application is large in size and its version is frequently changed, it is recommended to use Java Network Launching Protocol (JNLP) . JNLP is a protocol for the deployment and execution of software components. Using the protocol, a client application (hereafter client) can automatically be downloaded via the web server and executed. This is called Java Web Start. Like other clients, a client downloaded by JNLP can access JEUS.

JNLP makes it easier to deploy client programs because it automatically supplies with binaries required for version upgrade, enabling continual deployment. You can practice using the JNLP file with JNLP samples and the README file in sample\jnlp in the JDK home directory.

This section describes how to configure a web application.

Configuring Web Application

To obtain the JNLP file from the web and download the defined JAR files from the web server, the servlet that implements the JNLP protocol is required. Since the servlet is not provided by JEUS, use a sample JNLP servlet provided by JDK 1.7.

The jnlp-servlet.jar file, where the servlet is implemented, resides in the following directory of Sun JDK 1.7. (For IBM JDK 1.7, it exists in the lib directory.)

sample/jnlp/servlet

Copy the jnlp-servlet.jar file to WEB-INF/lib directory of the web application, and create the web.xml file as follows. When this is done, the servlet will transmit the JNLP and resource files to the client according to the JNLP protocol.

The following is an example of the web.xml file for JNLP servlet.

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
         http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
       <servlet-name>JnlpDownloadServlet</servlet-name>
       <servlet-class>jnlp.sample.servlet.JnlpDownloadServlet</servlet-class>
       <init-param>
           <param-name>logLevel</param-name>
           <param-value>DEBUG</param-value>
       </init-param>
       <init-param>
           <param-name>logPath</param-name>
           <param-value>jnlpdownloadservlet.log</param-value>
       </init-param>
  </servlet>
  <servlet-mapping>
      <servlet-name>JnlpDownloadServlet</servlet-name>
      <url-pattern>*.jnlp</url-pattern>
  </servlet-mapping>
</web-app>

The following is the source code for the HelloClient class. A JNLP client is not much different from normal clients. Since a JNLP client does not have a console window, like an applet, a GUI window is created by using Swing.

package helloejb;

import javax.naming.Context;
import javax.naming.InitialContext;
import java.util.Hashtable;

import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.event.*;

import javax.swing.*;

public class HelloClient extends JFrame {
   public static void main(String[] args)
   {
      new HelloClient();
   }

   public HelloClient() {
    try {
            Hashtable env = new Hashtable();
            env.put(Context.INITIAL_CONTEXT_FACTORY,"jeus.jndi.JNSContextFactory");
            Context context = new InitialContext(env);
            Hello hello = (Hello) context.lookup("helloejb.Hello");

            JLabel label = new JLabel(hello.sayHello());
            label.setFont(new Font("Helevetica", Font.BOLD, 15));
            getContentPane().setLayout(new BorderLayout());
            getContentPane().add(label, BorderLayout.CENTER);
            setSize(500, 250);
            setVisible(true);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
   }
}

Java Web Start requires a JNLP file containing information for executing HelloClient.

The following example specifies the JAR file to execute HelloClient, the Java version in use, etc. The '$$codebase' setting of the codebase attribute in the <jnlp> tag is automatically replaced according to the context used for deploying the web application including the JNLP servlets. In the example, since there is no path specified for the href attribute for the JAR file, JNLP file and JAR file should be placed in the same directory.

<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0" codebase="$$codebase">
   <information>
      <title>HelloClient</title>
      <vendor>TmaxSoft</vendor>
   </information>
   <resources>
      <j2se version="1.5+" href="http://java.sun.com/products/autodl/j2se"/>
      <jar href="hello-client.jar"/>
      <jar href="jclient.jar"/>
   </resources>
   <application-desc main-class="helloejb.HelloClient"/>
</jnlp>

This section explains how to execute a client.

http://host1:8088/hello/app/HelloClient.jnlp

package helloejb;

import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.event.*;

import javax.swing.*;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.ejb.EJB;

public class HelloClient extends JFrame {
   @EJB
   private static Hello hello;

   public static void main(String[] args) {
      new HelloClient();
   }

   public HelloClient() {
    try {
            JLabel label = new JLabel(hello.sayHello());
            label.setFont(new Font("Helevetica", Font.BOLD, 15));
            getContentPane().setLayout(new BorderLayout());
            getContentPane().add(label, BorderLayout.CENTER);
            setSize(500, 250);
            setVisible(true);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
   }
}

<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0" codebase="$$codebase">
   <information>
      <title>HelloClient</title>
      <vendor>TmaxSoft</vendor>
   </information>
   <security>
      <all-permissions/>
   </security>
   <resources>
      <j2se version="1.5+" href="http://java.sun.com/products/autodl/j2se"/>
      <jar href="clientcontainer.jar"/>
      <jar href="hello-client.jar"/>
      <property name="jeus.client.container.jws" value="true"/>
   </resources>
   <application-desc main-class="jeus.client.container.ClientContainer">
        <argument>-main</argument>
        <argument>helloejb.HelloClient</argument>
   </application-desc>
</jnlp>

keytool -genkey -alias helloclient -keypass 1234 -keystore helloks -storepass 1234
jarsigner -keystore helloks hello-client.jar helloclient