Tutorial 01 : JWS/JNLP Guide

•  Introduction

JWS (Java Web Start) is a deployment technology for Java applications through networks. This is used to simplify installation.
With a simple click on an internet browser, JWS download, install and execute any Java application using JNLP Java Network Launching Protocol.

The only need for the client site is that Java is installed on his system. JWS is included in the JRE (Java Runtime Environment) since Java 1.4.

We will see in this tutorial only what the client see.
 

•  Tutorial - Part 1

To deployable application appears like a classic link in a web page. This link points towards a JNLP file.

Look at this capture :

JNLP link

Now, what JWS do if you click on the link ?

If your browser associated JNLP file with JWS, you will see this download box :

Download JNLP file with Mozilla Firefox

Sorry by these French captures but I've got a French system.
May be one day I will take English captures or your captures submites.

After downloading the JNLP file (few ko), JWS start :
 

JWS launching

The JNLP file contains all the informations about the application that will be start.
It contains these informations :
  - application name and description.
  - author and certificate (for security purpose).
  - all requiered files : classes and libraries.
  - version of the JRE.
  - ...

Now, JWS downloads files (jogl.jar, jogl libraries, BaseCode.jar and Tutorial26.jar) :

Downloading requiered files

After that all files are downloaded, before the application is executed, you will be asked to accept or refuse the certificate. This is for security reason.
If you accept the certificate, the application will have all permissions (ie same permissions like when you run "classic" applications).

Certificate

If you want to have more informations on the certificate, press "More details" button :

Certificate details

Finally, the application is launched. You can notice the JWS console :

JWS console - Application launched

You can see in all of these steps that the client don't need to know anything about Java.

He just have to know how to install Java on his computer (ie go to sun site, download jre and click ok for installing).

Easy, no ?
 

• Tutorial - Part 2

We have seen that JWS download the application and cache the application locally.

How can I find where the application is cached ?

This is very simple, go to the installation folder of your JRE. Then, launch javaws from bin folder (ie C:\Java\jre1.5.0_05\bin\javaws.exe under Windows platform).

Javaws (JWS)

You can see the application launched previously with JWS.
The application is cache somewhere in you're hard drive (Documents and Settings/.../Sun under Windows platform). If you want to re-execute it, just double click on it.

With this panel, you can obtain some informations like the author site, the jnlp file ...
Here is the JNLP file associated with the application (OpenGl Tutorial 26) :

JNLP file

Java application launch externally to JWS are harder to run compared with binarie (exe) application generate by other langage like C++...
Because you need to specify where classes are stored, where to find libraries ...

I think that JWS is really cool because the user don't need to know nothing about Java to use the application. All is done automatically !