ClassNotFoundException - While Loading a Class Dynamically in a Web Application using ClassLoader

Question

I am trying to load a class dynamically using loadClass method of java ClassLoader in NetBeans IDE. When I run the following standalone program it gets executed properly and prints the output as expected:

public class StandaloneClass {

    public static void main(String[] args) {
        try {

            String directory = "C:\\Workspace\\ProjectMeteor\\src\\java\\com\\meteor\\loader";

            File file = new File(directory);
            URL url = file.toURI().toURL();
            URL[] urls = new URL[]{url};

            ClassLoader cl = new URLClassLoader(urls);

            Class cls = cl.loadClass("com.meteor.loader.ClassToBeLoaded");
            Object o = cls.newInstance();

            System.out.println("Class Loaded: " + o.getClass().toString());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

Output:- Class Loaded: class com.meteor.loader.ClassToBeLoaded

But when I run the same piece of code (in a web application) its throwing ClassNotFoundException.

@Path("/test")
public class DynamicWebClass {

    @GET
    @Path("/getFileExplorerNodes")
    @Produces(MediaType.TEXT_PLAIN)
    public String getFileExplorerNodes() {
        try {

            String directory = "C:\\Workspace\\ProjectMeteor\\src\\java\\com\\meteor\\loader";

            File file = new File(directory);
            URL url = file.toURI().toURL();
            URL[] urls = new URL[]{url};

            ClassLoader cl = new URLClassLoader(urls);

            Class cls = cl.loadClass("com.meteor.loader.ClassToBeLoaded");
            Object o = cls.newInstance();

            return o.getClass().toString();

        } catch (Exception e) {
            e.printStackTrace();
            return "error";
        }
    }

}

Output:-
java.lang.ClassNotFoundException: com.meteor.loader.ClassToBeLoaded

Why is it throwing exception in web application when it is working fine in standalone program? How to fix this issue and make it run properly in a web application as well?

Yes. The class is there in the war. And the war is present under dist folder of the project. — Quick_Silver
– Quick_Silver, Commented Oct 20, 2014 at 12:28
But you are pointing to some other directory in C:/. Provide a relative url — dasrohith
– dasrohith, Commented Oct 20, 2014 at 12:34

dasrohith · Accepted Answer · 2014-10-20 12:47:32Z

1

Looks like problem with the URL provided to the Class loader. Please provide a relative URL

answered Oct 20, 2014 at 12:47

dasrohith

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1 Comment

Quick_Silver Over a year ago

Thank you very much for the information. Especially for pointing my url to the war. Alternatively, we can replace URLClassLoader with the default one. ClassLoader cl = DynamicWebClass.class.getClassLoader();

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