DUBBO-78 JVM之间共享长连接 HedlerExchangeHandler改回实现ChannelHandlerDelegate接口，并返回传入的Handler，解决问题：

1.ExchangeHandler提供了getExchangeHandler方法，该方法强制对handler进行转型。如果不返回传入的Handler，会导致强制转型失败

2.AbstractPeer中增加getDelegateChannelHandler方法，返回最终的handler，以便上层调用getHandler时，并通过handler直接处理消息时可以不丢失HeaderExchangeHandler的行为。

此处需要在后续考虑架构的调整，当前实现不优雅，


git-svn-id: http://code.alibabatech.com/svn/dubbo/trunk@461 1a56cb94-b969-4eaa-88fa-be21384802f2

dubbo-remoting/src/main/java/com/alibaba/dubbo/remoting/exchange/support/header/HeaderExchangeHandler.java

@@ -28,6 +28,7 @@ import com.alibaba.dubbo.remoting.exchange.ExchangeHandler;
 import com.alibaba.dubbo.remoting.exchange.Request;
 import com.alibaba.dubbo.remoting.exchange.Response;
 import com.alibaba.dubbo.remoting.exchange.support.DefaultFuture;
+import com.alibaba.dubbo.remoting.transport.ChannelHandlerDelegate;
 
 /**
  * ExchangeReceiver
@@ -35,8 +36,7 @@ import com.alibaba.dubbo.remoting.exchange.support.DefaultFuture;
  * @author william.liangf
  * @author chao.liuc
  */
-//如果实现implementChannelHandlerDelegate，方法getHandler需要返回this.否则getHandler返回的是ExchangeHandler，将丢失本handler附加的功能.
-public class HeaderExchangeHandler implements ChannelHandler {
+public class HeaderExchangeHandler implements ChannelHandlerDelegate {
 
     protected static final Logger logger              = LoggerFactory.getLogger(HeaderExchangeHandler.class);
 
@@ -205,4 +205,12 @@ public class HeaderExchangeHandler implements ChannelHandler {
             HeaderExchangeChannel.removeChannelIfDisconnected(channel);
         }
     }
+
+    public ChannelHandler getHandler() {
+        if (handler instanceof ChannelHandlerDelegate) {
+            return ((ChannelHandlerDelegate) handler).getHandler();
+        } else {
+            return handler;
+        }
+    }
 }
\ No newline at end of file

dubbo-remoting/src/main/java/com/alibaba/dubbo/remoting/transport/AbstractPeer.java

@@ -83,7 +83,23 @@ public abstract class AbstractPeer implements Endpoint, ChannelHandler {
             return handler;
         }
     }
-
+    
+    /**
+     * @return
+     */
+    @Deprecated
+    public ChannelHandler getHandler() {
+        return getDelegateHandler();
+    }
+    
+    /**
+     * 返回最终的handler，可能已被wrap,需要区别于getChannelHandler
+     * @return
+     */
+    public ChannelHandler getDelegateHandler() {
+        return handler;
+    }
+    
     public boolean isClosed() {
         return closed;
     }
@@ -121,9 +137,4 @@ public abstract class AbstractPeer implements Endpoint, ChannelHandler {
         }
         handler.caught(ch, ex);
     }
-
-    @Deprecated
-    public ChannelHandler getHandler() {
-        return getChannelHandler();
-    }
 }