Jim Yu wrote:
2009/6/18 Regis <[email protected]>
Jim Yu wrote:
2009/6/18 Regis <[email protected]>
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.
Verified at r786379. Thanks, Regis.
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.
I found this patch involve serious performance regression. Because
Proxy.isProxyClass() synchronized on a instance "proxyCache", which is a static
field of Proxy, so all HashMap.get() will contend for this lock. So is there
other way to test whether a class is Proxy class or Proxy.isProxyClass() could
avoid to use lock of static field?
--
Best Regards,
Regis.
