How to dynamically Add Classess to Running VMs class path

[echarish Kumar]

Hi All,

I want to know how can i add classess from a jar through code to the running VM's class path. i want this because a user cn upload a JAR and the classess in that JAR shoud get loded into the SYSTEM Class loader.

I will really appriciate if someone can explain this by a code example.

[Tim McGuire]

This is what Class.forName() is for
check out http://java.sun.com/developer/technicalArticles/ALT/Reflection/


allowing a user to upload any class at all is a huge security problem though.

[Rob Spoor]

Not quite Tim. The JAR files need to be added to the system class loader, and that is the tricky part. A URLClassLoader can load JAR files on the fly but it's not the system class loader.

[Tim McGuire]

Rob Prime wrote:Not quite Tim. The JAR files need to be added to the system class loader, and that is the tricky part. A URLClassLoader can load JAR files on the fly but it's not the system class loader.

missing piece added. Thanks Rob.

[echarish Kumar]

Thanks both of you for your replies , but still i have not got my Answer

[Vivek K Singh]

As rob said, It will be done by the URLClassLoader Check the doc URLClassLoader

URL[] urlArray = new URL[]{new File("myJarFile").toURL()};
URLClassLoader loader = new URLClassLoader(urlArray);
Class class1 = loader.loadClass("x.x.x.MyClass"); // binary name of the class like java.lang.String or java.net.URLClassLoader$3$1

[Rob Spoor]

I just remembered you can use Thread.setContextClassLoader to change the default class loader for a thread.

You may also want to subclass URLClassLoader to make the addURL method public:

class DynamicURLClassLoader extends URLClassLoader
{
    // constructors go here

    public void addURL(URL url)
    {
        super.addURL(url);
    }
}