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From "Joerg Schaible (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DBCP-358) Equals implementations in DelegatingXxx classes are not symmetric
Date Tue, 03 May 2011 00:34:03 GMT

    [ https://issues.apache.org/jira/browse/DBCP-358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13027957#comment-13027957
] 

Joerg Schaible commented on DBCP-358:
-------------------------------------

This behavior is unfortunately used in the PoolableManagedConnection w/ TransactionRegistry.
When a new connection is created in the pool, the unwrapped connection is registered (and
used as key in the internal WeakHashMap). Later on the wrapped connection is used to unregister
again (or to lookup the XAResource as done in org.apache.commons.dbcp.managed.TestBasicManagedDataSource.testReallyClose()).
As workaround it is possible to wrap the registered connection if it is not wrapped yet:

{noformat}
Index: src/java/org/apache/commons/dbcp/managed/TransactionRegistry.java
===================================================================
--- src/java/org/apache/commons/dbcp/managed/TransactionRegistry.java   (revision 1098813)
+++ src/java/org/apache/commons/dbcp/managed/TransactionRegistry.java   (working copy)
@@ -28,7 +28,9 @@
 import javax.transaction.TransactionManager;
 import javax.transaction.xa.XAResource;
 
+import org.apache.commons.dbcp.DelegatingConnection;
 
+
 /**
  * TransactionRegistry tracks Connections and XAResources in a transacted environment for
a single XAConnectionFactory.
  * </p>
@@ -62,7 +64,10 @@
     public synchronized void registerConnection(Connection connection, XAResource xaResource)
{
         if (connection == null) throw new NullPointerException("connection is null");
         if (xaResource == null) throw new NullPointerException("xaResource is null");
-        xaResources.put(connection, xaResource);
+        Connection key = connection instanceof DelegatingConnection 
+            ? connection 
+            : new DelegatingConnection(connection);
+        xaResources.put(key, xaResource);
     }
 
     /**
{noformat}

This approach will also solve DBCP-356 (another workaround is to use a HasMap instead of a
WeakHashMap for the XAResources).

> Equals implementations in DelegatingXxx classes are not symmetric
> -----------------------------------------------------------------
>
>                 Key: DBCP-358
>                 URL: https://issues.apache.org/jira/browse/DBCP-358
>             Project: Commons Dbcp
>          Issue Type: Bug
>    Affects Versions: 1.2, 1.2.2, 1.3, 1.4
>            Reporter: Phil Steitz
>             Fix For: 1.3.1, 1.4.1
>
>
> For reasons unclear to me, DelegatingConnection, DelegatingStatement, PoolGuardConnectionWrappers
and other DBCP classes implement equals so that the wrapping class is considered equal to
its innermost delegate JDBC object.  This makes equals asymmetric when applied to a wrapper
and its wrapped JDBC object - wrapper.equals(delegate) returns true, but delegate.equals(wrapper)
will in general return false.
> I am pretty sure that DBCP itself does not rely on this bugged behavior, so I am inclined
to fix it, making equals an equivalence relation on wrapper instances, with two considered
equal iff their innermost delegates are equal.  I can't imagine use cases where the bugged
behavior is required.  Can anyone else?

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