Dynamic Proxy with Exceptions

["Edward Sumerfield" <esumerfd@xxxxxxxxxxx>]

I want to create a dynamic proxy that can call a method that might throw an exception. When this method does throw I get an java.lang.reflect.UndeclaredThrowableException exception and am not sure what the fix is. The "testThrowException" test is the one that fails.

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import junit.framework.TestCase;

/**
 * @author Ed Sumerfield
 */
public class DynamicProxyTest extends TestCase
{
    private ProxyTestInterface m_proxy;

    /* (non-Javadoc)
     * @see junit.framework.TestCase#setUp()
     */
    protected void setUp() throws Exception
    {
        ProxyTestImpl impl = new ProxyTestImpl();
        Class[] arguments = new Class[] { ProxyTestInterface.class };
        InvocationHandler proxyImpl = new ProxyTestProxy(impl);

        m_proxy = (ProxyTestInterface)Proxy.newProxyInstance(impl.getClass()
            .getClassLoader(), arguments, proxyImpl);
    }

    /**
     * Prove that we can call a proxy method
     */
    public void testCallProxyMethod()
    {
        m_proxy.aMethod();
    }

    /**
     * Prove that we can call a proxy method and pass in an argument
     */
    public void testCallProxyMethodWithArgs()
    {
        m_proxy.aMethodWithArgs("hello world");
    }

    /**
     * Prove that an exception can be thrown from the delegate.
     * @throws Exception
     */
    public void testThrowException() throws Throwable
    {
        try
        {
            m_proxy.aMethodWithAnException();
            fail("Should have thrown exception");
        }
        catch (ProxyTestException e)
        {
            // Success
        }
    }
}

interface ProxyTestInterface
{
    public void aMethod();
    public void aMethodWithArgs(String a_text);
    public void aMethodWithAnException() throws ProxyTestException;
}

class ProxyTestImpl implements ProxyTestInterface
{
    public void aMethod()
    {
        System.out.println("aMethod called");
    }

    public void aMethodWithArgs(String a_text)
    {
        System.out.println("aMethodWithArgs called: " + a_text);
    }

    public void aMethodWithAnException() throws ProxyTestException
    {
        System.out.println("aMethodWithAnException called");
        throw new ProxyTestException();
    }
}

class ProxyTestProxy implements InvocationHandler
{
    private ProxyTestInterface m_impl;

    public ProxyTestProxy(ProxyTestInterface a_impl)
    {
        m_impl = a_impl;
    }

    public Object invoke(Object a_proxy, Method a_method, Object[] a_args)
            throws Throwable
    {
        System.out.println("Proxy calling: " + a_method.getName());
        return a_method.invoke(m_impl, a_args);
    }
}

class ProxyTestException extends Exception
{
}

 

Ed