Re: [classlib][luni] HashMap doesn't support proxy object as keys

[Regis]

Jim Yu wrote:

2009/6/18 Regis <xu.re...@gmail.com>

Jim Yu wrote:

Hi all,

There is an interesting edge case in HashMap. If we use a proxy object as
the key to put something into HashMap, we will fail to retrieve the value
by
using that key. But RI works well for this case. Here is a test case below
to present the problem. I found the root cause of the failure for our
HashMap is that proxyInstance.equals(proxyInstance) returns false which
sounds strange but appears work correctly as both Harmony and RI behave
so.

It's very interesting behaviors, seems like RI did it intended, are there
any cases we need proxyInstance.equals(proxyInstance) return false?

I think it is reasonable to return false here since spec mentioned for proxy
instance that "An invocation of the hashCode, equals, or toString methods
declared in java.lang.Object on a proxy instance will be encoded and
dispatched to the invocation handler's invoke method" So the meaning of
equals method seems has been changed by the invoke here: )

 I suspect RI has made some special approaches to match the key when the

key
is a proxy object. So I would be inclined to follow RI's behavior in this
case. Any thoughts here?

I think if proxyInstance.equals(proxyInstance) return false is reasonable,
we should do some tricks to make HashMap work with Proxy. And does Proxy
object work well with other collections which used equals to retrieve object
from collection?

Agree. I have made a patch to do the trick so as to follow RI's behavior.

The patch looks good for me, applied at r786015, please verify.

I have raised a JIRA at
https://issues.apache.org/jira/browse/HARMONY-6237for this issue.


public interface MockInterface {
   public String mockMethod();
}

public class MockClass implements MockInterface {
   public String mockMethod() {
       return "This is a mock class.";
   }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;

public class TestProxy implements InvocationHandler {

   Object obj;

   public TestProxy(Object o) {
       obj = o;
   }

   public Object invoke(Object proxy, Method m, Object[] args)
           throws Throwable {

       Object result = null;

       try {

           result = m.invoke(obj, args);

       } catch (Exception e) {
           e.printStackTrace();
       } finally {
       }
       return result;
   }

   public static void main(String[] argv) throws Exception {

       MockInterface proxyInstance = (MockInterface)
Proxy.newProxyInstance(
               MockInterface.class.getClassLoader(),
               new Class[] { MockInterface.class }, new TestProxy(
                       new MockClass()));

       Map hm = new HashMap();

       hm.put(proxyInstance, "Value");

       Object o = hm.get(proxyInstance);

       System.out.println("Value got for proxy object key:" + o);

       System.out.println(proxyInstance.equals(proxyInstance));

   }
}

Output
Harmony:
Value got for proxy object key:null
false

RI:
Value got for proxy object key:Value
false

--
Best Regards,
Regis.

--
Best Regards,
Regis.