Channel (Netty API Reference (5.0.0.Alpha2))

All Superinterfaces:

AttributeMap, Comparable<Channel>

All Known Subinterfaces:

DatagramChannel, DomainSocketChannel, SctpChannel, SctpServerChannel, ServerChannel, ServerDomainSocketChannel, ServerSocketChannel, SocketChannel, UdtChannel, UdtServerChannel, UnixChannel

All Known Implementing Classes:

AbstractChannel, AbstractEpollServerChannel, AbstractEpollStreamChannel, AbstractNioByteChannel, AbstractNioChannel, AbstractNioMessageChannel, AbstractOioByteChannel, AbstractOioChannel, AbstractOioMessageChannel, AbstractServerChannel, EmbeddedChannel, EpollDatagramChannel, EpollDomainSocketChannel, EpollServerDomainSocketChannel, EpollServerSocketChannel, EpollSocketChannel, LocalChannel, LocalServerChannel, NioDatagramChannel, NioSctpChannel, NioSctpServerChannel, NioServerSocketChannel, NioSocketChannel, NioUdtAcceptorChannel, NioUdtByteAcceptorChannel, NioUdtByteConnectorChannel, NioUdtByteRendezvousChannel, NioUdtMessageAcceptorChannel, NioUdtMessageConnectorChannel, NioUdtMessageRendezvousChannel, OioByteStreamChannel, OioDatagramChannel, OioSctpChannel, OioSctpServerChannel, OioServerSocketChannel, OioSocketChannel, RxtxChannel
```
public interface Channel
extends AttributeMap, Comparable<Channel>
```
A nexus to a network socket or a component which is capable of I/O operations such as read, write, connect, and bind.
A channel provides a user:
- the current state of the channel (e.g. is it open? is it connected?),
- the configuration parameters of the channel (e.g. receive buffer size),
- the I/O operations that the channel supports (e.g. read, write, connect, and bind), and
- the ChannelPipeline which handles all I/O events and requests associated with the channel.
All I/O operations are asynchronous.

All I/O operations in Netty are asynchronous. It means any I/O calls will return immediately with no guarantee that the requested I/O operation has been completed at the end of the call. Instead, you will be returned with a ChannelFuture instance which will notify you when the requested I/O operation has succeeded, failed, or canceled.
Channels are hierarchical

A Channel can have a parent depending on how it was created. For instance, a SocketChannel, that was accepted by ServerSocketChannel, will return the ServerSocketChannel as its parent on parent().
The semantics of the hierarchical structure depends on the transport implementation where the Channel belongs to. For example, you could write a new Channel implementation that creates the sub-channels that share one socket connection, as BEEP and SSH do.
Downcast to access transport-specific operations

Some transports exposes additional operations that is specific to the transport. Down-cast the Channel to sub-type to invoke such operations. For example, with the old I/O datagram transport, multicast join / leave operations are provided by DatagramChannel.
Release resources

It is important to call close() or close(ChannelPromise) to release all resources once you are done with the Channel. This ensures all resources are released in a proper way, i.e. filehandles.

Nested Class Summary

Nested Classes
Modifier and Type Interface and Description

static interface Channel.Unsafe
Unsafe operations that should never be called from user-code.

Nested Classes
Modifier and Type	Interface and Description
`static interface`	`Channel.Unsafe` Unsafe operations that should never be called from user-code.

Method Summary

Methods
Modifier and Type	Method and Description
`ByteBufAllocator`	`alloc()` Return the assigned `ByteBufAllocator` which will be used to allocate `ByteBuf`s.
`ChannelFuture`	`bind(SocketAddress localAddress)` Request to bind to the given `SocketAddress` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`bind(SocketAddress localAddress, ChannelPromise promise)` Request to bind to the given `SocketAddress` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`close()` Request to close this `Channel` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`close(ChannelPromise promise)` Request to close this `Channel` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`closeFuture()` Returns the `ChannelFuture` which will be notified when this channel is closed.
`ChannelConfig`	`config()` Returns the configuration of this channel.
`ChannelFuture`	`connect(SocketAddress remoteAddress)` Request to connect to the given `SocketAddress` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`connect(SocketAddress remoteAddress, ChannelPromise promise)` Request to connect to the given `SocketAddress` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`connect(SocketAddress remoteAddress, SocketAddress localAddress)` Request to connect to the given `SocketAddress` while bind to the localAddress and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise)` Request to connect to the given `SocketAddress` while bind to the localAddress and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`deregister()` Request to deregister this `Channel` from its assigned `EventLoop` and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`deregister(ChannelPromise promise)` Request to deregister this `Channel` from its assigned `EventLoop` and notify the `ChannelPromise` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`disconnect()` Request to disconnect from the remote peer and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`ChannelFuture`	`disconnect(ChannelPromise promise)` Request to disconnect from the remote peer and notify the `ChannelFuture` once the operation completes, either because the operation was successful or because of an error.
`EventLoop`	`eventLoop()` Return the `EventLoop` this `Channel` was registered too.
`Channel`	`flush()` Request to flush all pending messages.
`ChannelId`	`id()` Returns the globally unique identifier of this `Channel`.
`boolean`	`isActive()` Return `true` if the `Channel` is active and so connected.
`boolean`	`isOpen()` Returns `true` if the `Channel` is open an may get active later
`boolean`	`isRegistered()` Returns `true` if the `Channel` is registered with an `EventLoop`.
`boolean`	`isWritable()` Returns `true` if and only if the I/O thread will perform the requested write operation immediately.
`SocketAddress`	`localAddress()` Returns the local address where this channel is bound to.
`ChannelMetadata`	`metadata()` Return the `ChannelMetadata` of the `Channel` which describe the nature of the `Channel`.
`ChannelFuture`	`newFailedFuture(Throwable cause)` Create a new `ChannelFuture` which is marked as failed already.
`ChannelProgressivePromise`	`newProgressivePromise()` Return an new `ChannelProgressivePromise`
`ChannelPromise`	`newPromise()` Return a new `ChannelPromise`.
`ChannelFuture`	`newSucceededFuture()` Create a new `ChannelFuture` which is marked as succeeded already.
`Channel`	`parent()` Returns the parent of this channel.
`ChannelPipeline`	`pipeline()` Return the assigned `ChannelPipeline`
`Channel`	`read()` Request to Read data from the `Channel` into the first inbound buffer, triggers an `ChannelHandler.channelRead(ChannelHandlerContext, Object)` event if data was read, and triggers a `channelReadComplete` event so the handler can decide to continue reading.
`SocketAddress`	`remoteAddress()` Returns the remote address where this channel is connected to.
`Channel.Unsafe`	`unsafe()` Returns an internal-use-only object that provides unsafe operations.
`ChannelPromise`	`voidPromise()` Return a special ChannelPromise which can be reused for different operations.
`ChannelFuture`	`write(Object msg)` Request to write a message via this `Channel` through the `ChannelPipeline`.
`ChannelFuture`	`write(Object msg, ChannelPromise promise)` Request to write a message via this `Channel` through the `ChannelPipeline`.
`ChannelFuture`	`writeAndFlush(Object msg)` Shortcut for call `write(Object)` and `flush()`.
`ChannelFuture`	`writeAndFlush(Object msg, ChannelPromise promise)` Shortcut for call `write(Object, ChannelPromise)` and `flush()`.

Methods inherited from interface io.netty.util.AttributeMap
attr, hasAttr

Methods inherited from interface java.lang.Comparable
compareTo

- Method Detail
  - id
```
ChannelId id()
```
    Returns the globally unique identifier of this Channel.
  - eventLoop
```
EventLoop eventLoop()
```
    Return the EventLoop this Channel was registered too.
  - parent
```
Channel parent()
```
    Returns the parent of this channel.
    
    Returns:
    the parent channel. null if this channel does not have a parent channel.
  - config
```
ChannelConfig config()
```
    Returns the configuration of this channel.
  - isOpen
```
boolean isOpen()
```
    Returns true if the Channel is open an may get active later
  - isRegistered
```
boolean isRegistered()
```
    Returns true if the Channel is registered with an EventLoop.
  - isActive
```
boolean isActive()
```
    Return true if the Channel is active and so connected.
  - metadata
```
ChannelMetadata metadata()
```
    Return the ChannelMetadata of the Channel which describe the nature of the Channel.
  - localAddress
```
SocketAddress localAddress()
```
    Returns the local address where this channel is bound to. The returned SocketAddress is supposed to be down-cast into more concrete type such as InetSocketAddress to retrieve the detailed information.
    
    Returns:
    the local address of this channel. null if this channel is not bound.
  - remoteAddress
```
SocketAddress remoteAddress()
```
    Returns the remote address where this channel is connected to. The returned SocketAddress is supposed to be down-cast into more concrete type such as InetSocketAddress to retrieve the detailed information.
    
    Returns:
    the remote address of this channel. null if this channel is not connected. If this channel is not connected but it can receive messages from arbitrary remote addresses (e.g. DatagramChannel, use DefaultAddressedEnvelope.recipient() to determine the origination of the received message as this method will return null.
  - closeFuture
```
ChannelFuture closeFuture()
```
    Returns the ChannelFuture which will be notified when this channel is closed. This method always returns the same future instance.
  - isWritable
```
boolean isWritable()
```
    Returns true if and only if the I/O thread will perform the requested write operation immediately. Any write requests made when this method returns false are queued until the I/O thread is ready to process the queued write requests.
  - unsafe
```
Channel.Unsafe unsafe()
```
    Returns an internal-use-only object that provides unsafe operations.
  - pipeline
```
ChannelPipeline pipeline()
```
    Return the assigned ChannelPipeline
  - alloc
```
ByteBufAllocator alloc()
```
    Return the assigned ByteBufAllocator which will be used to allocate ByteBufs.
  - newPromise
```
ChannelPromise newPromise()
```
    Return a new ChannelPromise.
  - newProgressivePromise
```
ChannelProgressivePromise newProgressivePromise()
```
    Return an new ChannelProgressivePromise
  - newSucceededFuture
```
ChannelFuture newSucceededFuture()
```
    Create a new ChannelFuture which is marked as succeeded already. So Future.isSuccess() will return true. All FutureListener added to it will be notified directly. Also every call of blocking methods will just return without blocking.
  - newFailedFuture
```
ChannelFuture newFailedFuture(Throwable cause)
```
    Create a new ChannelFuture which is marked as failed already. So Future.isSuccess() will return false. All FutureListener added to it will be notified directly. Also every call of blocking methods will just return without blocking.
  - voidPromise
```
ChannelPromise voidPromise()
```
    Return a special ChannelPromise which can be reused for different operations.
    It's only supported to use it for write(Object, ChannelPromise).
    
    Be aware that the returned ChannelPromise will not support most operations and should only be used if you want to save an object allocation for every write operation. You will not be able to detect if the operation was complete, only if it failed as the implementation will call ChannelPipeline.fireExceptionCaught(Throwable) in this case.
    Be aware this is an expert feature and should be used with care!
  - bind
```
ChannelFuture bind(SocketAddress localAddress)
```
    Request to bind to the given SocketAddress and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error.
    This will result in having the ChannelHandler.bind(ChannelHandlerContext, SocketAddress, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - connect
```
ChannelFuture connect(SocketAddress remoteAddress)
```
    Request to connect to the given SocketAddress and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error.
    If the connection fails because of a connection timeout, the ChannelFuture will get failed with a ConnectTimeoutException. If it fails because of connection refused a ConnectException will be used.
    This will result in having the ChannelHandler.connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - connect
```
ChannelFuture connect(SocketAddress remoteAddress,
                    SocketAddress localAddress)
```
    Request to connect to the given SocketAddress while bind to the localAddress and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error.
    This will result in having the ChannelHandler.connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - disconnect
```
ChannelFuture disconnect()
```
    Request to disconnect from the remote peer and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error.
    This will result in having the ChannelHandler.disconnect(ChannelHandlerContext, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - close
```
ChannelFuture close()
```
    Request to close this Channel and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error. After it is closed it is not possible to reuse it again.
    This will result in having the ChannelHandler.close(ChannelHandlerContext, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - deregister
```
ChannelFuture deregister()
```
    Request to deregister this Channel from its assigned EventLoop and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error.
    This will result in having the ChannelHandler.deregister(ChannelHandlerContext, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
    After this method completes (not the ChannelFuture!) one can not submit new tasks to the Channel's EventLoop until the Channel is again registered with an EventLoop. Any attempt to do so will result in a RejectedExecutionException being thrown. Any tasks that were submitted before the call to deregister() will finish before the ChannelFuture completes. Furthermore, periodic and delayed tasks will not be executed until the Channel is registered with an EventLoop again. Theses are tasks submitted to the EventLoop via one of the methods declared by ScheduledExecutorService. Please note that all of the above only applies to tasks created from within the deregistered Channel's ChannelHandlers.
    It's only safe to EventLoopGroup.register(Channel) the Channel with another (or the same) EventLoop after the ChannelFuture has completed.
  - bind
```
ChannelFuture bind(SocketAddress localAddress,
                 ChannelPromise promise)
```
    Request to bind to the given SocketAddress and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error. The given ChannelPromise will be notified.
    This will result in having the ChannelHandler.bind(ChannelHandlerContext, SocketAddress, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - connect
```
ChannelFuture connect(SocketAddress remoteAddress,
                    ChannelPromise promise)
```
    Request to connect to the given SocketAddress and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error. The given ChannelFuture will be notified.
    If the connection fails because of a connection timeout, the ChannelFuture will get failed with a ConnectTimeoutException. If it fails because of connection refused a ConnectException will be used.
    This will result in having the ChannelHandler.connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - connect
```
ChannelFuture connect(SocketAddress remoteAddress,
                    SocketAddress localAddress,
                    ChannelPromise promise)
```
    Request to connect to the given SocketAddress while bind to the localAddress and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error. The given ChannelPromise will be notified and also returned.
    This will result in having the ChannelHandler.connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - disconnect
```
ChannelFuture disconnect(ChannelPromise promise)
```
    Request to disconnect from the remote peer and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error. The given ChannelPromise will be notified.
    This will result in having the ChannelHandler.disconnect(ChannelHandlerContext, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - close
```
ChannelFuture close(ChannelPromise promise)
```
    Request to close this Channel and notify the ChannelFuture once the operation completes, either because the operation was successful or because of an error. After it is closed it is not possible to reuse it again. The given ChannelPromise will be notified.
    This will result in having the ChannelHandler.close(ChannelHandlerContext, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - deregister
```
ChannelFuture deregister(ChannelPromise promise)
```
    Request to deregister this Channel from its assigned EventLoop and notify the ChannelPromise once the operation completes, either because the operation was successful or because of an error.
    This will result in having the ChannelHandler.deregister(ChannelHandlerContext, ChannelPromise) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
    After this method completes (not the ChannelPromise!) one can not submit new tasks to the Channel's EventLoop until the Channel is again registered with an EventLoop. Any attempt to do so will result in a RejectedExecutionException being thrown. Any tasks that were submitted before the call to deregister() will finish before the ChannelPromise completes. Furthermore, periodic and delayed tasks will not be executed until the Channel is registered with an EventLoop again. Theses are tasks submitted to the EventLoop via one of the methods declared by ScheduledExecutorService. Please note that all of the above only applies to tasks created from within the deregistered Channel's ChannelHandlers.
    It's only safe to EventLoopGroup.register(Channel) the Channel with another (or the same) EventLoop after the ChannelPromise has completed.
  - read
```
Channel read()
```
    Request to Read data from the Channel into the first inbound buffer, triggers an ChannelHandler.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 ChannelHandler.read(ChannelHandlerContext) method called of the next ChannelHandler contained in the ChannelPipeline of the Channel.
  - write
```
ChannelFuture write(Object msg)
```
    Request to write a message via this Channel through the ChannelPipeline. This method will not request to actual flush, so be sure to call flush() once you want to request to flush all pending data to the actual transport.
  - write
```
ChannelFuture write(Object msg,
                  ChannelPromise promise)
```
    Request to write a message via this Channel through the ChannelPipeline. This method will not request to actual flush, so be sure to call flush() once you want to request to flush all pending data to the actual transport.
  - flush
```
Channel flush()
```
    Request to flush all pending messages.
  - writeAndFlush
```
ChannelFuture writeAndFlush(Object msg,
                          ChannelPromise promise)
```
    Shortcut for call write(Object, ChannelPromise) and flush().
  - writeAndFlush
```
ChannelFuture writeAndFlush(Object msg)
```
    Shortcut for call write(Object) and flush().

Interface Channel

All I/O operations are asynchronous.

Channels are hierarchical

Downcast to access transport-specific operations

Release resources

Nested Class Summary

Method Summary

Methods inherited from interface io.netty.util.AttributeMap

Methods inherited from interface java.lang.Comparable

Method Detail

id

eventLoop

parent

config

isOpen

isRegistered

isActive

metadata

localAddress

remoteAddress

closeFuture

isWritable

unsafe

pipeline

alloc

newPromise

newProgressivePromise

newSucceededFuture

newFailedFuture

voidPromise

bind

connect

connect

disconnect

close

deregister

bind

connect

connect

disconnect

close

deregister

read

write

write

flush

writeAndFlush

writeAndFlush