ChannelHandlerContext (Netty API Reference (4.1.115.Final))

All Superinterfaces:

AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker
```
public interface ChannelHandlerContext
extends AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker
```
Enables a ChannelHandler to interact with its ChannelPipeline and other handlers. Among other things a handler can notify the next ChannelHandler in the ChannelPipeline as well as modify the ChannelPipeline it belongs to dynamically.
Notify
You can notify the closest handler in the same ChannelPipeline by calling one of the various methods provided here. Please refer to ChannelPipeline to understand how an event flows.
Modifying a pipeline
You can get the ChannelPipeline your handler belongs to by calling pipeline(). A non-trivial application could insert, remove, or replace handlers in the pipeline dynamically at runtime.
Retrieving for later use
You can keep the ChannelHandlerContext for later use, such as triggering an event outside the handler methods, even from a different thread.
```
 public class MyHandler extends ChannelDuplexHandler {

     private ChannelHandlerContext ctx;

     public void beforeAdd(ChannelHandlerContext ctx) {
         this.ctx = ctx;
     }

     public void login(String username, password) {
         ctx.write(new LoginMessage(username, password));
     }
     ...
 }
 
```
Storing stateful information
attr(AttributeKey) allow you to store and access stateful information that is related with a ChannelHandler / Channel and its context. Please refer to ChannelHandler to learn various recommended ways to manage stateful information.
A handler can have more than one ChannelHandlerContext
Please note that a 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 ChannelHandlerContexts if it is added to one or more ChannelPipelines more than once. Also note that a ChannelHandler that is supposed to be added to multiple ChannelPipelines should be marked as ChannelHandler.Sharable.
Additional resources worth reading

Please refer to the ChannelHandler, and ChannelPipeline to find out more about inbound and outbound operations, what fundamental differences they have, how they flow in a pipeline, and how to handle the operation in your application.

Method Summary

All Methods Instance Methods Abstract Methods Deprecated Methods
Modifier and Type	Method and Description
`ByteBufAllocator`	`alloc()` Return the assigned `ByteBufAllocator` which will be used to allocate `ByteBuf`s.
`<T> Attribute<T>`	`attr(AttributeKey<T> key)` Deprecated. Use `AttributeMap.attr(AttributeKey)`
`Channel`	`channel()` Return the `Channel` which is bound to the `ChannelHandlerContext`.
`EventExecutor`	`executor()` Returns the `EventExecutor` which is used to execute an arbitrary task.
`ChannelHandlerContext`	`fireChannelActive()` A `Channel` is active now, which means it is connected.
`ChannelHandlerContext`	`fireChannelInactive()` A `Channel` is inactive now, which means it is closed.
`ChannelHandlerContext`	`fireChannelRead(Object msg)` A `Channel` received a message.
`ChannelHandlerContext`	`fireChannelReadComplete()` Triggers an `ChannelInboundHandler.channelReadComplete(ChannelHandlerContext)` event to the next `ChannelInboundHandler` in the `ChannelPipeline`.
`ChannelHandlerContext`	`fireChannelRegistered()` A `Channel` was registered to its `EventLoop`.
`ChannelHandlerContext`	`fireChannelUnregistered()` A `Channel` was unregistered from its `EventLoop`.
`ChannelHandlerContext`	`fireChannelWritabilityChanged()` Triggers an `ChannelInboundHandler.channelWritabilityChanged(ChannelHandlerContext)` event to the next `ChannelInboundHandler` in the `ChannelPipeline`.
`ChannelHandlerContext`	`fireExceptionCaught(Throwable cause)` A `Channel` received an `Throwable` in one of its inbound operations.
`ChannelHandlerContext`	`fireUserEventTriggered(Object evt)` A `Channel` received an user defined event.
`ChannelHandlerContext`	`flush()` Request to flush all pending messages via this ChannelOutboundInvoker.
`ChannelHandler`	`handler()` The `ChannelHandler` that is bound this `ChannelHandlerContext`.
`<T> boolean`	`hasAttr(AttributeKey<T> key)` Deprecated. Use `AttributeMap.hasAttr(AttributeKey)`
`boolean`	`isRemoved()` Return `true` if the `ChannelHandler` which belongs to this context was removed from the `ChannelPipeline`.
`String`	`name()` The unique name of the `ChannelHandlerContext`.The name was used when then `ChannelHandler` was added to the `ChannelPipeline`.
`ChannelPipeline`	`pipeline()` Return the assigned `ChannelPipeline`
`ChannelHandlerContext`	`read()` Request to Read data from the `Channel` into the first inbound buffer, triggers an `ChannelInboundHandler.channelRead(ChannelHandlerContext, Object)` event if data was read, and triggers a `channelReadComplete` event so the handler can decide to continue reading.

Methods inherited from interface io.netty.channel.ChannelOutboundInvoker
bind, bind, close, close, connect, connect, connect, connect, deregister, deregister, disconnect, disconnect, newFailedFuture, newProgressivePromise, newPromise, newSucceededFuture, voidPromise, write, write, writeAndFlush, writeAndFlush

- Method Detail
  - channel
```
Channel channel()
```
    Return the Channel which is bound to the ChannelHandlerContext.
  - executor
```
EventExecutor executor()
```
    Returns the EventExecutor which is used to execute an arbitrary task.
  - name
```
String name()
```
    The unique name of the ChannelHandlerContext.The name was used when then ChannelHandler was added to the ChannelPipeline. This name can also be used to access the registered ChannelHandler from the ChannelPipeline.
  - handler
```
ChannelHandler handler()
```
    The ChannelHandler that is bound this ChannelHandlerContext.
  - isRemoved
```
boolean isRemoved()
```
    Return true if the ChannelHandler which belongs to this context was removed from the ChannelPipeline. Note that this method is only meant to be called from with in the EventLoop.
  - fireChannelRegistered
```
ChannelHandlerContext fireChannelRegistered()
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel was registered to its EventLoop. This will result in having the ChannelInboundHandler.channelRegistered(ChannelHandlerContext) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireChannelRegistered in interface ChannelInboundInvoker
  - fireChannelUnregistered
```
ChannelHandlerContext fireChannelUnregistered()
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel was unregistered from its EventLoop. This will result in having the ChannelInboundHandler.channelUnregistered(ChannelHandlerContext) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireChannelUnregistered in interface ChannelInboundInvoker
  - fireChannelActive
```
ChannelHandlerContext fireChannelActive()
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel is active now, which means it is connected. This will result in having the ChannelInboundHandler.channelActive(ChannelHandlerContext) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireChannelActive in interface ChannelInboundInvoker
  - fireChannelInactive
```
ChannelHandlerContext fireChannelInactive()
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel is inactive now, which means it is closed. This will result in having the ChannelInboundHandler.channelInactive(ChannelHandlerContext) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireChannelInactive in interface ChannelInboundInvoker
  - fireExceptionCaught
```
ChannelHandlerContext fireExceptionCaught(Throwable cause)
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel received an Throwable in one of its inbound operations. This will result in having the ChannelInboundHandler.exceptionCaught(ChannelHandlerContext, Throwable) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireExceptionCaught in interface ChannelInboundInvoker
  - fireUserEventTriggered
```
ChannelHandlerContext fireUserEventTriggered(Object evt)
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel received an user defined event. This will result in having the ChannelInboundHandler.userEventTriggered(ChannelHandlerContext, Object) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireUserEventTriggered in interface ChannelInboundInvoker
  - fireChannelRead
```
ChannelHandlerContext fireChannelRead(Object msg)
```
    Description copied from interface: ChannelInboundInvoker
    
    A Channel received a message. This will result in having the ChannelInboundHandler.channelRead(ChannelHandlerContext, Object) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    fireChannelRead in interface ChannelInboundInvoker
  - fireChannelReadComplete
```
ChannelHandlerContext fireChannelReadComplete()
```
    Description copied from interface: ChannelInboundInvoker
    
    Triggers an ChannelInboundHandler.channelReadComplete(ChannelHandlerContext) event to the next ChannelInboundHandler in the ChannelPipeline.
    
    Specified by:
    
    fireChannelReadComplete in interface ChannelInboundInvoker
  - fireChannelWritabilityChanged
```
ChannelHandlerContext fireChannelWritabilityChanged()
```
    Description copied from interface: ChannelInboundInvoker
    
    Triggers an ChannelInboundHandler.channelWritabilityChanged(ChannelHandlerContext) event to the next ChannelInboundHandler in the ChannelPipeline.
    
    Specified by:
    
    fireChannelWritabilityChanged in interface ChannelInboundInvoker
  - read
```
ChannelHandlerContext read()
```
    Description copied from interface: ChannelOutboundInvoker
    
    Request to Read data from the Channel into the first inbound buffer, triggers an ChannelInboundHandler.channelRead(ChannelHandlerContext, Object) event if data was read, and triggers a channelReadComplete event so the handler can decide to continue reading. If there's a pending read operation already, this method does nothing.
    This will result in having the ChannelOutboundHandler.read(ChannelHandlerContext) method called of the next ChannelOutboundHandler contained in the ChannelPipeline of the Channel.
    
    Specified by:
    
    read in interface ChannelOutboundInvoker
  - flush
```
ChannelHandlerContext flush()
```
    Description copied from interface: ChannelOutboundInvoker
    
    Request to flush all pending messages via this ChannelOutboundInvoker.
    
    Specified by:
    
    flush in interface ChannelOutboundInvoker
  - pipeline
```
ChannelPipeline pipeline()
```
    Return the assigned ChannelPipeline
  - alloc
```
ByteBufAllocator alloc()
```
    Return the assigned ByteBufAllocator which will be used to allocate ByteBufs.
  - attr
```
@Deprecated
<T> Attribute<T> attr(AttributeKey<T> key)
```
    Deprecated. Use AttributeMap.attr(AttributeKey)
    
    Description copied from interface: AttributeMap
    
    Get the Attribute for the given AttributeKey. This method will never return null, but may return an Attribute which does not have a value set yet.
    
    Specified by:
    
    attr in interface AttributeMap
  - hasAttr
```
@Deprecated
<T> boolean hasAttr(AttributeKey<T> key)
```
    Deprecated. Use AttributeMap.hasAttr(AttributeKey)
    
    Description copied from interface: AttributeMap
    
    Returns true if and only if the given Attribute exists in this AttributeMap.
    
    Specified by:
    
    hasAttr in interface AttributeMap

Interface ChannelHandlerContext

Notify

Modifying a pipeline

Retrieving for later use

Storing stateful information

A handler can have more than one `ChannelHandlerContext`

Additional resources worth reading

Method Summary

Methods inherited from interface io.netty.channel.ChannelOutboundInvoker

Method Detail

channel

executor

name

handler

isRemoved

fireChannelRegistered

fireChannelUnregistered

fireChannelActive

fireChannelInactive

fireExceptionCaught

fireUserEventTriggered

fireChannelRead

fireChannelReadComplete

fireChannelWritabilityChanged

read

flush

pipeline

alloc

attr

hasAttr

Interface ChannelHandlerContext

Notify

Modifying a pipeline

Retrieving for later use

Storing stateful information

A handler can have more than one ChannelHandlerContext

Additional resources worth reading

Method Summary

Methods inherited from interface io.netty.channel.ChannelOutboundInvoker

Method Detail

channel

executor

name

handler

isRemoved

fireChannelRegistered

fireChannelUnregistered

fireChannelActive

fireChannelInactive

fireExceptionCaught

fireUserEventTriggered

fireChannelRead

fireChannelReadComplete

fireChannelWritabilityChanged

read

flush

pipeline

alloc

attr

hasAttr

A handler can have more than one `ChannelHandlerContext`