A Dangerous Use of Proxy Names

package simmons.robert;
 
/*
 * $Proxy0 $Proxy0
 */
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
 
/*
 * 
 * This software is granted under the terms of the Common Public License, CPL, which may be found at
 * the following URL: http://www-124.ibm.com/developerworks/oss/CPLv1.0.htm
 * 
 * Copyright(c) 2003-2005 by the authors indicated in the @author tags. All Rights are Reserved by
 * the various authors.
 * 
 * ########## DO NOT EDIT ABOVE THIS LINE ##########
 */
 
/**
 * Demonstrates a dangerous use of proxy names.
 * 
 * <p>
 * According to the JDK, the unqualified name of a proxy class is undefined so using it in code like
 * this could cause you grief.
 * </p>
 * 
 * @author <a href=mailto:kraythe@arcor.de>Robert Simmons jr. (kraythe)</a>
 * @version $Revision: 1.2 $
 */
public class DangerousNames {
    /**
     * Run the demonstration.
     * 
     * @param args
     *            Command line arguments (ignored).
     */
    public static final void main(final String[] args) {
	SomeClass proxy = SomeClassFactory.getDynamicSomeClassProxy();
	System.out.println(proxy.getClass().getName());
	try {
	    Class cl = Class.forName("$Proxy0"); // <== Dangerous!
	    System.out.println(cl.getName());
	} catch (final ClassNotFoundException ex) {
	    ex.printStackTrace();
	}
    }
}
 
class SomeClassFactory {
 
    /**
     * Gets a counting proxy to an object that is constructed with the user name.
     * 
     * @return The proxy to the implementation.
     */
    public static final SomeClassCountingProxy getCountingProxy() {
	SomeClassImpl impl = new SomeClassImpl(System.getProperty("user.name"));
	return new SomeClassCountingProxy(impl);
    }
 
    /**
     * Gets proxy to depending upon debug status in Log4J.
     * 
     * @return The proxy to the implementation.
     */
    public static final SomeClass getDynamicSomeClassProxy() {
	SomeClassImpl impl = new SomeClassImpl(System.getProperty("user.name"));
	InvocationHandler handler = new MethodCountingHandler(impl);
	Class[] interfaces = new Class[] { SomeClass.class };
	ClassLoader loader = SomeClassFactory.class.getClassLoader();
	SomeClass proxy = (SomeClass) Proxy.newProxyInstance(loader, interfaces, handler);
	return proxy;
    }
 
    /**
     * Gets a proxy to an object that is constructed with the user name.
     * 
     * @return The proxy to the implementation.
     */
    public static final SomeClassProxy getProxy() {
	SomeClassImpl impl = new SomeClassImpl(System.getProperty("user.name"));
	return new SomeClassProxy(impl);
    }
 
    /**
     * Gets proxy to depending upon debug status in Log4J.
     * 
     * @return The proxy to the implementation.
     */
    public static final SomeClass getSomeClassProxy() {
	SomeClassImpl impl = new SomeClassImpl(System.getProperty("user.name"));
	if (true) {
	    return new SomeClassCountingProxy(impl);
	} else {
	    return new SomeClassProxy(impl);
	}
    }
}
 
class SomeClassCountingProxy implements SomeClass {
    /** The implementation object for this proxy. */
    private final SomeClassImpl impl;
 
    /** Holds the invocation count. */
    private int invocationCount = 0;
 
    /**
     * Creates a new SomeClassProxy object.
     * 
     * @param impl
     *            The implementation object for this proxy.
     */
    public SomeClassCountingProxy(final SomeClassImpl impl) {
	this.impl = impl;
    }
 
    /**
     * Gets the value of the property invocationCount.
     * 
     * @return The current value of invocationCount
     */
    public int getInvocationCount() {
	return invocationCount;
    }
 
    /**
     * @see java2s.hcj.proxies.SomeClass#someMethod()
     */
    public void someMethod() {
	this.invocationCount++;
	this.impl.someMethod();
    }
 
    /**
     * @see java2s.hcj.proxies.SomeClass#someOtherMethod(java.lang.String)
     */
    public void someOtherMethod(String text) {
	this.invocationCount++;
	this.impl.someOtherMethod(text);
    }
}
 
class SomeClassImpl implements SomeClass {
    /** Holds the user name. */
    private String userName;
 
    /**
     * Creates a new SomeClass object.
     * 
     * @param userName
     *            The user name to use.
     */
    public SomeClassImpl(final String userName) {
	this.userName = userName;
    }
 
    /**
     * @see java2s.hcj.proxies.SomeClass#someOtherMethod(java.lang.String)
     */
    public void someMethod() {
	System.out.println(this.userName);
    }
 
    /**
     * @see java2s.hcj.proxies.SomeClass#someOtherMethod(java.lang.String)
     */
    public void someOtherMethod(final String text) {
	System.out.println(text);
    }
}
 
class SomeClassProxy implements SomeClass {
    /** The impl object for this proxy. */
    private final SomeClassImpl impl;
 
    /**
     * Creates a new SomeClassProxy object.
     * 
     * @param impl
     *            The implementation object for this proxy.
     */
    public SomeClassProxy(final SomeClassImpl impl) {
	this.impl = impl;
    }
 
    /**
     * @see java2s.hcj.proxies.SomeClass#someMethod()
     */
    public void someMethod() {
	this.impl.someMethod();
    }
 
    /**
     * @see java2s.hcj.proxies.SomeClass#someOtherMethod(java.lang.String)
     */
    public void someOtherMethod(String text) {
	this.impl.someOtherMethod(text);
    }
}
 
interface SomeClass {
    /**
     * Print out the user name.
     */
    public abstract void someMethod();
 
    /**
     * Print out the string given to us.
     * 
     * @param text
     *            The string to print.
     */
    public abstract void someOtherMethod(final String text);
}
 
/**
 * An invocation handler that counts the number of calls for all methods in the target class.
 * 
 * @author <a href=mailto:kraythe@arcor.de>Robert Simmons jr. (kraythe)</a>
 * @version $Revision: 1.2 $
 * 
 * @see java.lang.reflect.InvocationHandler
 */
class MethodCountingHandler implements InvocationHandler {
    /** The implementation object for this proxy. */
    private final Object impl;
 
    /** Holds the invocation count. */
    private int invocationCount = 0;
 
    /**
     * Creates a new MethodCOuntingHandler object.
     * 
     * @param impl
     */
    public MethodCountingHandler(final Object impl) {
	this.impl = impl;
    }
 
    /**
     * Gets the value of the property invocationCount.
     * 
     * @return The current value of invocationCount
     */
    public int getInvocationCount() {
	return invocationCount;
    }
 
    /**
     * @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object, java.lang.reflect.Method,
     *      java.lang.Object[])
     */
    public Object invoke(Object proxy, Method meth, Object[] args) throws Throwable {
	try {
	    this.invocationCount++;
	    Object result = meth.invoke(impl, args);
	    return result;
	} catch (final InvocationTargetException ex) {
	    throw ex.getTargetException();
	}
    }
}