Re: add jar to classpath at runtime but not able to access resource in jar

From:

Alessio Stalla <alessiostalla@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 20 Apr 2010 06:21:38 -0700 (PDT)

Message-ID:

<495ec267-98c7-42be-9d00-83bf55833515@r28g2000vbi.googlegroups.com>

On Apr 20, 11:24 am, mike <mikaelpetter...@hotmail.com> wrote:

On 20 Apr, 10:50, Alessio Stalla <alessiosta...@gmail.com> wrote:

On Apr 20, 10:04 am, mike <mikaelpetter...@hotmail.com> wrote:

Hi,

I have exteneded URLClassLoader to:

import java.net.URL;
import java.net.URLClassLoader;

/**
* The ExtenedClassLoader class.
*/
public class ExtendedClassLoader extends URLClassLoader {
    /**
     * @param urls, to carryforward the existing classpath.
     */
    public ExtendedClassLoader(URL[] urls) {
        super(urls);
    }

    @Override
    /**
     * add ckasspath to the loader.
     */
    public void addURL(URL url) {
        super.addURL(url);
    }

}

Then to add my jar file to classpath at runtime I use the following
code ( see below).

private void addToClasspath(){
        try
        {
            URL urls [] = {};

            String path = "/home/xddmid/out/xml.jar";
            String urlPath = "jar:file://" + path + "!/=

URL url = new URL (urlPath);
ExtendedClassLoader cl = new ExtendedClassL=

oader (urls);

cl.addURL(url);
String resource =
ClassLoader.getSystemClassLoader().getResource("test.xml").toExternal=

Form();

System.out.println ("Success! Resource "+reso=

urce + "

found!");
        }
        catch (Exception ex)
        {
            System.out.println ("Failed.");
            ex.printStackTrace ();
        }

I have verified that the jarfile exists and that it contains "test.xm=

file" ( "jar tvf xml.jar).
The "test.xml" file is directly in root ( no package name).

I get a NullPointerException for this line:

String resource =
ClassLoader.getSystemClassLoader().getResource("test.xml").toExternal=

Form();

Why are you using the system classloader and not the one you wrote? In
other words, that should be cl.getResource...

Alessio

This line is used in code to access system resources. I cannot change
it.

ClassLoader.getSystemClassLoader().getResource("test.xml").toExternalForm=

();

Then you cannot dynamically add jars to the classpath. Problem
solved. ;)

Alessio