public interface ChannelHandlerContext
ChannelHandler
to interact with its ChannelPipeline
and other handlers. A handler can send a ChannelEvent
upstream or
downstream, modify the ChannelPipeline
it belongs to dynamically.
ChannelEvent
to the closest handler in the
same ChannelPipeline
by calling sendUpstream(ChannelEvent)
or sendDownstream(ChannelEvent)
. Please refer to
ChannelPipeline
to understand how an event flows.
ChannelPipeline
your handler belongs to by calling
getPipeline()
. A non-trivial application could insert, remove, or
replace handlers in the pipeline dynamically in runtime.
ChannelHandlerContext
for later use, such as
triggering an event outside the handler methods, even from a different thread.
public class MyHandler extendsSimpleChannelHandler
implementsLifeCycleAwareChannelHandler
{ privateChannelHandlerContext
ctx; public void beforeAdd(ChannelHandlerContext
ctx) { this.ctx = ctx; } public void login(String username, password) {Channels
.write( this.ctx,Channels
.succeededFuture(this.ctx.getChannel()), new LoginMessage(username, password)); } ... }
setAttachment(Object)
and getAttachment()
allow you to
store and access stateful information that is related with a handler and its
context. Please refer to ChannelHandler
to learn various recommended
ways to manage stateful information.
ChannelHandler
instance can be added to more than
one ChannelPipeline
. It means a single ChannelHandler
instance can have more than one ChannelHandlerContext
and therefore
the single instance can be invoked with different
ChannelHandlerContext
s if it is added to one or more
ChannelPipeline
s more than once.
For example, the following handler will have as many independent attachments as how many times it is added to pipelines, regardless if it is added to the same pipeline multiple times or added to different pipelines multiple times:
public class FactorialHandler extendsSimpleChannelHandler
{ // This handler will receive a sequence of increasing integers starting // from 1.@Override
public void messageReceived(ChannelHandlerContext
ctx,MessageEvent
evt) { Integer a = (Integer) ctx.getAttachment(); Integer b = (Integer) evt.getMessage(); if (a == null) { a = 1; } ctx.setAttachment(Integer.valueOf(a * b)); } } // Different context objects are given to "f1", "f2", "f3", and "f4" even if // they refer to the same handler instance. Because the FactorialHandler // stores its state in a context object (as an attachment), the factorial is // calculated correctly 4 times once the two pipelines (p1 and p2) are active. FactorialHandler fh = new FactorialHandler();ChannelPipeline
p1 =Channels
.pipeline(); p1.addLast("f1", fh); p1.addLast("f2", fh);ChannelPipeline
p2 =Channels
.pipeline(); p2.addLast("f3", fh); p2.addLast("f4", fh);
Please refer to the ChannelHandler
, ChannelEvent
, and
ChannelPipeline
to find out what a upstream event and a downstream
event are, what fundamental differences they have, how they flow in a
pipeline, and how to handle the event in your application.
Modifier and Type | Method and Description |
---|---|
boolean |
canHandleDownstream()
|
boolean |
canHandleUpstream()
|
Object |
getAttachment()
Retrieves an object which is
attached to
this context. |
Channel |
getChannel()
Returns the
Channel that the ChannelPipeline belongs to. |
ChannelHandler |
getHandler()
Returns the
ChannelHandler that this context object is
serving. |
String |
getName()
Returns the name of the
ChannelHandler in the
ChannelPipeline . |
ChannelPipeline |
getPipeline()
Returns the
ChannelPipeline that the ChannelHandler
belongs to. |
void |
sendDownstream(ChannelEvent e)
Sends the specified
ChannelEvent to the
ChannelDownstreamHandler which is placed in the closest
downstream from the handler associated with this context. |
void |
sendUpstream(ChannelEvent e)
Sends the specified
ChannelEvent to the
ChannelUpstreamHandler which is placed in the closest upstream
from the handler associated with this context. |
void |
setAttachment(Object attachment)
Attaches an object to this context to store a stateful information
specific to the
ChannelHandler which is associated with this
context. |
Channel getChannel()
Channel
that the ChannelPipeline
belongs to.
This method is a shortcut to getPipeline().getChannel().ChannelPipeline getPipeline()
ChannelPipeline
that the ChannelHandler
belongs to.String getName()
ChannelHandler
in the
ChannelPipeline
.ChannelHandler getHandler()
ChannelHandler
that this context object is
serving.boolean canHandleUpstream()
boolean canHandleDownstream()
void sendUpstream(ChannelEvent e)
ChannelEvent
to the
ChannelUpstreamHandler
which is placed in the closest upstream
from the handler associated with this context. It is recommended to use
the shortcut methods in Channels
rather than calling this method
directly.void sendDownstream(ChannelEvent e)
ChannelEvent
to the
ChannelDownstreamHandler
which is placed in the closest
downstream from the handler associated with this context. It is
recommended to use the shortcut methods in Channels
rather than
calling this method directly.Object getAttachment()
attached
to
this context.null
if no object was attached or
null
was attachedvoid setAttachment(Object attachment)
ChannelHandler
which is associated with this
context.Copyright © 2008-2014 The Netty Project. All Rights Reserved.