Load class from Jar file

[Azriel Abramovich]

I have my own class loader, and I wish to load a class from a Jar file.
How do I do it?
I have overridden the

  
public Class findClass(String name) {
    byte[] b = readClass(name);
       //invoke the super-classes method
    return defineClass(name, b, 0, b.length);
}
private byte[] readClass(String name) {
    byte[] ret = null;
    InputStream in = null;
    try {
in = new BufferedInputStream(
                 new FileInputStream("myFolder/"+name + ".class"));
ret = new byte[in.available()];
in.read(ret);
    } catch (Exception e) {
in.close();
    }
    return ret;
}

How do I read the class from the Jar file
Thanks!

[David O'Meara]

Do you need to write your own ClassLoader? You can use a URLClassLoader to load the class from a JAR file, unless you need some specific behaviour not provided by the existing ClassLoaders.
Even if you do, you can extend the URLClassLoader, override the bits you need, then delegate the 'loading of classes from jar files' bit to the parent.
The following code uses aURLClassLoader to load a class from a JAR file.

        //create two ClassLoaders with different
        URL[] classpath = { new File("dir1/my.jar").toURL() };
        URLClassLoader cl = new URLClassLoader( classpath, null );
        Class clazz = Class.forName("com.javaranch.davo.MyClass",true,cl);

Note you'll have to play with the dir1/my.jar part to get it working correctly.
Dave

[Azriel Abramovich]

Thanx!