Java Web Start Resource Loading Tutorial

In this tutorial I create a real-world example that loads resources (e.g. properties and images) from a jar to make the app Java Web Start ready.

• Browse the Source
• Launch Hello Venus Tutorial Example

Here is a first impression of the Hello Venus resource loading example. The icons are retrieved from the jar as well as menu.properties which is used to create the help menu.

Retrieving resources from jars isn't hard if you use the resource anchor trick presented here.

Start with creating an empty class and package it with your resources. Example:

public class ResourceAnchor
{
    public ResourceAnchor()
    {
    }
}

The ResourceAnchor class is just here to identify the Java archive that holds your resources. There is no need to burn the weather report on your toast in the constructor.

Here is the content of tutorial.jar that holds ResourceAnchor.class and all resources we want to retrieve:

vamp/tutorial/CmdShowUrl.class
vamp/tutorial/HelloVenus$1.class
vamp/tutorial/HelloVenus.class
vamp/tutorial/Main.class
vamp/tutorial/menu.properties
vamp/tutorial/ResourceAnchor.class
vamp/tutorial/WebBrowser.class
vamp/tutorial/images/inform.gif
vamp/tutorial/images/world2.gif

To retrieve your resources you need to get a hand on a class loader. Here's the pick-up line:

ClassLoader cl = ResourceAnchor.class.getClassLoader();

Now, you are ready to drill for bits. Here is how you get an icon from tutorial.jar:

URL worldIconUrl = cl.getResource( "vamp/tutorial/images/world2.gif" );
ImageIcon worldIcon = new ImageIcon( worldIconUrl );

Or in compressed form:

ImageIcon worldIcon = new ImageIcon( cl.getResource( "vamp/tutorial/images/world2.gif" ) );

Tip: Use only lower case resource names as on some machines retrieving resources with both upper and lower case letters will fail (e.g rename World2.gif to world2.gif).

And here is how to get menu.properties from tutorial.jar:

Properties props = new Properties();
try
{
  props.load( cl.getResourceAsStream( "vamp/tutorial/menu.properties"  ));
}
catch( IOException ioex )
{
  System.err.println( "*** failed to load properties: " + ioex.toString() );
}

That's it. That's all there is to it.