JNLP: Delivering client-side Java programs using browser

Recently we made a swing application for one of our clients. It was meant to be just a tool for the APIs that we wrote for the client, to facilitate the business people to get a hand of the system. But now as with most of the projects the requirement changed. The UI that we made was meant to work over browser and should be available over intranet. This was a complete surprise for us, as now the application needs to be converted from Swing to Applet, which is a bit unstable as it gives its own set of security concerns.

Not feeling quite optimistic about converting the UI I started to look at options that can help us out to put desktop application on browser. It was then I started playing with Java network launch protocol(JNLP) and Java Webstart.

Unlike other browser-based applications Webstart applications run outside the browser but are delivered through a standard Web server. These applications get downloaded on client machine then get installed and run from the local client machine. You can have newer version of a Webstart application and it will get downloaded on the client automatically , whenever the client runs it the next time.

Now in order to convert a standard java application to a Webstart application you need to do quite some work as specified by SUN tutorial. Following are the steps in brief:

1. Generate a key
2. Create a JNLP specification file
3. Pack the whole stuff in a jar
4. Sign the Jar using the key
5. create a war for the application using signed jars
6. Deploy it into a web server.

Or we can use the maven webstart plugin for generating the signed jars and maybe use assembly plugin to get a deployable War. The plugin works quite out of the box with some initial configuration as specified on the plugin page. It has its own set of sample templates that can be used to generate the JNLP file for the application.

Following is the snapshot of the configuration that I used to generate the signed jars.:

<plugin>
<groupId>org.codehaus.mojo.webstart</groupId>
<artifactId>webstart-maven-plugin</artifactId>
<configuration>
<dependencies>
<includes>
<include>commons-lang:commons-lang</include>
<include>commons-io:commons-io</include>
</includes>
</dependencies>
<jnlp>
myApp.jnlp <!– defaults to launch.jnlp –>
<mainClass>com.sample.HelloWorld</mainClass>
</jnlp>
<sign>
<keystore>pass</keystore>
<keypass>pass</keypass>
<storepass>pass
<alias>hello</alias>
<dnameCn>MyName</dnameCn>
<verify>true</verify>
<keystoreConfig>
true <!– delete the keystore –>
<gen>true</gen>       <!– optional shortcut to generate the store. –>
</keystoreConfig>
</sign>
<pack200>true</pack200>
<gzip>true</gzip>
<outputJarVersions>false</outputJarVersions>
</configuration>
</plugin>

The plugin works with webstart :jnlp goal. Then I packed the jars generated using the assembly plugin and integrated it into the build.

The plugin also provides a mechanism to configure JnlpDownloadServlet class that can be used to generate Wars which can automatically suit to your context path. It has a sample template which can be used with the webstart:jnlp-servelet goal. But I faced some issues with it and was unable to use it successfully. With the task of generating this War as time-boxed I resorted to my earlier attempt of using webstart:jnlp goal along with assembly plugin and integrated it into build process.

PS: If someone is able to work with JnlpDownloadServlet using webstart plugin do tell me 🙂

Resources:

http://java.sun.com/developer/technicalArticles/Programming/jnlp/

http://mojo.codehaus.org/webstart/webstart-maven-plugin/

http://java.sun.com/javase/6/docs/technotes/guides/javaws/developersguide/downloadservletguide.html