URLClassLOader无法从jar动态加载类

Question

   URLClassLoader child;
   try {
       child = new URLClassLoader(new URL[]{myJar.toURI().toURL()}, Test2.class.getClassLoader());
       child.loadClass("com.bla.bla.StringUtilService");
   } catch (MalformedURLException | ClassNotFoundException ex) {
       ex.printStackTrace();
   }

I am getting ClassNotFoundException in loadClass .

I have tried several variants of the code such as

URL[] urls = { new URL("jar:file:" + "E:\\Works\\Workspace\\JUnit_Proj\\client.jar"+"!/") };
URLClassLoader cl = URLClassLoader.newInstance(urls);

But all results into ClassNotFoundException !

I have tried debugging in Eclipse, but the class loader instance is unable to load classes from the jar. The classes Vector is empty.

Answer 1

Succeeded using different costructor of URLClassLoader.

    try {
        File jarFile = new File("D:\\Workspace\\Test\\Test.jar");
        URLClassLoader loader = new URLClassLoader(new URL[]{jarFile.toURI().toURL()});

        Class.forName("com.bla.bla.HelloWorld", true, loader);
        System.out.println("Success");
        loader.close();
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

Answer 2

The class is a direct child of the dir in the url, so you need no package.

Try this without the package. Like this:

URLClassLoader child;
try {
    child = new URLClassLoader(new URL[]{myJar.toURI().toURL()}, Test2.class.getClassLoader());
    child.loadClass("StringUtilService");
} catch (MalformedURLException | ClassNotFoundException ex) {
    ex.printStackTrace();
}

Also, try like this:

URLClassLoader child;
try {
    child = new URLClassLoader(new URL[]{myJar.toURI().toURL()}, getClass().class.getClassLoader());
    child.loadClass("StringUtilService");
} catch (MalformedURLException | ClassNotFoundException ex) {
    ex.printStackTrace();
}

Solution from: ClassNotFoundException while loading a class from file with URLClassLoader