Question

I use the asm to implements a proxy patterns.
for example:
the original class is test.service.Service

public class ProxyFactory{
    public static Object generateProxy(Class<?> argument){
        //do generate use asm. 
        //generate a proxyClass that extends argument
        //and override the sayHello() method
        //and than invoke System.out.println("anything") before we call super.sayHello()
        Class<?> class = proxyClass;
        return class.newInstance();
    }
}


public class Service implements IService{
    @Override
    public List<String> sayHello(){
        List<String> list = new ArrayList<String>();
        list.add("stackoverflow user");
        return list;
    }
}

public class Action extends ActionSupport{

     private IService service = ProxyFactory.generateProxy(Service.class);

}

When I request this action than will be an Exception:

java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
…
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NoClassDefFoundError: test.service.Service
at java.lang.ClassLoader.defineClass1(Native Method)
…
… 40 more
Caused by: java.lang.ClassNotFoundException: test.service.Service
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
…
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
… 43 more

It’s seem like tomcat classloader problem because all above code can work if I run it as application could you anybody help me to solve it.
Thank

Answer 1

Solve by myself, actually , As I expected, the problem is caused by classloader.
this is before code:

byte[] b = class byte code...
ClassLoder loader = ClassLoader.getSystemClassLoader();
Class<?> cls = Class.forName("java.lang.ClassLoader");
java.lang.reflect.Method method = cls.getDeclaredMethod(
                "defineClass", new Class[] { String.class, byte[].class,
                        int.class, int.class });
method.setAccessible(true);
Object[] args = new Object[] { sc.getName(), b, new Integer(0),
                    new Integer(b.length) };
clazz = (Class<?>) method.invoke(loader, args);

and now i use Thread.currentThread().getContextClassLoader() to instead of
ClassLoader.getSystemClassLoader();

it mean we can use tomcat classloader to defined our class so than can found our web
application class “test.service.Service”