Interface ChannelDownstreamHandler

All Superinterfaces:
All Known Implementing Classes:
Base64Encoder, BufferedWriteHandler, ChunkedWriteHandler, CompatibleObjectEncoder, ExecutionHandler, HttpClientCodec, HttpContentCompressor, HttpContentEncoder, HttpMessageEncoder, HttpRequestEncoder, HttpResponseEncoder, HttpServerCodec, IdleStateAwareChannelHandler, LengthFieldPrepender, LoggingHandler, ObjectEncoder, OneToOneEncoder, ProtobufEncoder, ProtobufVarint32LengthFieldPrepender, RtspMessageEncoder, RtspRequestEncoder, RtspResponseEncoder, SimpleChannelDownstreamHandler, SimpleChannelHandler, SslHandler, StringEncoder, WebSocketFrameEncoder, WriteTimeoutHandler, ZlibEncoder

public interface ChannelDownstreamHandler
extends ChannelHandler

Handles or intercepts a downstream ChannelEvent, and sends a ChannelEvent to the next handler in a ChannelPipeline.

The most common use case of this interface is to intercept an I/O request such as Channel.write(Object) and Channel.close().


In most cases, you will get to use a SimpleChannelDownstreamHandler to implement a downstream handler because it provides an individual handler method for each event type. You might want to implement this interface directly though if you want to handle various types of events in more generic way.

Firing an event to the next handler

You can forward the received event downstream or upstream. In most cases, ChannelDownstreamHandler will send the event downstream (i.e. outbound) although it is legal to send the event upstream (i.e. inbound):

 // Sending the event downstream (outbound)
 void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e) throws Exception {

 // Sending the event upstream (inbound)
 void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
     ctx.sendUpstream(new UpstreamChannelStateEvent(...));

Using the helper class to send an event

You will also find various helper methods in Channels to be useful to generate and send an artificial or manipulated event.

State management

Please refer to ChannelHandler.

Thread safety

handleDownstream may be invoked by more than one thread simultaneously. If the handler accesses a shared resource or stores stateful information, you might need proper synchronization in the handler implementation.

$Rev: 2122 $, $Date: 2010-02-02 11:00:04 +0900 (Tue, 02 Feb 2010) $
The Netty Project, Trustin Lee

Nested Class Summary
Nested classes/interfaces inherited from interface
Method Summary
 void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)
          Handles the specified downstream event.

Method Detail


void handleDownstream(ChannelHandlerContext ctx,
                      ChannelEvent e)
                      throws Exception
Handles the specified downstream event.

ctx - the context object for this handler
e - the downstream event to process or intercept

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