/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

	Copyright (c) Non, Inc. 1999 -- All Rights Reserved

PACKAGE:	JavaWorld
FILE:		JarClassLoader.java

AUTHOR:		John D. Mitchell, Mar  3, 1999

REVISION HISTORY:
	Name	Date		Description
	----	----		-----------
	JDM	99.03.03   	Initial version.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/


/**
 ** JarClassLoader provides a minimalistic ClassLoader which shows how to
 ** instantiate a class which resides in a .jar file.
<br><br>
 **
 ** @author	John D. Mitchell, Non, Inc., Mar  3, 1999
 **
 ** @version 0.5
 **
 **/

public class JarClassLoader extends MultiClassLoader
    {
    private JarResources	jarResources;

    public JarClassLoader (String jarName)
	{
	// Create the JarResource and suck in the .jar file.
	jarResources = new JarResources (jarName);
	}

    protected byte[] loadClassBytes (String className)
	{
	// Support the MultiClassLoader's class name munging facility.
	className = formatClassName (className);

	// Attempt to get the class data from the JarResource.
	return (jarResources.getResource (className));
	}


    /*
     * Internal Testing application.
     */
    public static class Test
	{
	public static void main(String[] args) throws Exception
	    {
	    if (args.length != 2)
		{
		System.err.println
		    ("Usage: java JarClassLoader " +
		     "<jar file name> <class name>");
		System.exit (1);
		}

	    /*
	     * Create the .jar class loader and use the first argument
	     * passed in from the command line as the .jar file to use.
	     */
	    JarClassLoader jarLoader = new JarClassLoader (args [0]);

	    /* Load the class from the .jar file and resolve it.	*/
	    Class c = jarLoader.loadClass (args [1], true);

	    /*
	     * Create an instance of the class.
	     *
	     * Note that created object's constructor-taking-no-arguments
	     * will be called as part of the objects creation.
	     */
	    Object o = c.newInstance();

	    /* Are we using a class that we specifically know about?	*/
	    if (o instanceof TestClass)
		{
		// Yep, lets call a method that we know about.	*/
		TestClass tc = (TestClass) o;
		tc.doSomething();
		}
	    }
	}	// End of nested Class Test.
    
    }	// End of Class JarClassLoader.