Package org.jboss.netty.channel

Interface Channel

All Superinterfaces:
Comparable<Channel>
All Known Subinterfaces:
DatagramChannel, LocalChannel, LocalServerChannel, ServerChannel, ServerSocketChannel, SocketChannel
All Known Implementing Classes:
AbstractChannel, AbstractNioChannel, AbstractOioChannel, AbstractServerChannel, DefaultLocalChannel, DefaultLocalServerChannel, EmbeddedChannel, HttpTunnelingClientSocketChannel, NioAcceptedSocketChannel, NioClientSocketChannel, NioDatagramChannel, NioServerSocketChannel, NioSocketChannel, OioAcceptedSocketChannel, OioClientSocketChannel, OioDatagramChannel, OioServerSocketChannel, OioSocketChannel
public interface Channel extends 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 getParent().

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.

InterestOps

A Channel has a property called interestOps which is similar to that of NIO SelectionKey. It is represented as a bit field which is composed of the two flags.

  • OP_READ - If set, a message sent by a remote peer will be read immediately. If unset, the message from the remote peer will not be read until the OP_READ flag is set again (i.e. read suspension).
  • OP_WRITE - If set, a write request will not be sent to a remote peer until the OP_WRITE flag is cleared and the write request will be pending in a queue. If unset, the write request will be flushed out as soon as possible from the queue.
  • OP_READ_WRITE - This is a combination of OP_READ and OP_WRITE, which means only write requests are suspended.
  • OP_NONE - This is a combination of (NOT OP_READ) and (NOT OP_WRITE), which means only read operation is suspended.

You can set or clear the OP_READ flag to suspend and resume read operation via setReadable(boolean).

Please note that you cannot suspend or resume write operation just like you can set or clear OP_READ. The OP_WRITE flag is read only and provided simply as a mean to tell you if the size of pending write requests exceeded a certain threshold or not so that you don't issue too many pending writes that lead to an OutOfMemoryError. For example, the NIO socket transport uses the writeBufferLowWaterMark and writeBufferHighWaterMark properties in NioSocketChannelConfig to determine when to set or clear the OP_WRITE flag.

  • Field Details

  • Method Details

    • getId

      Integer getId()
      Returns the unique integer ID of this channel.

    • getFactory

      ChannelFactory getFactory()
      Returns the ChannelFactory which created this channel.

    • getParent

      Channel getParent()
      Returns the parent of this channel.
      Returns:
      the parent channel. null if this channel does not have a parent channel.

    • getConfig

      ChannelConfig getConfig()
      Returns the configuration of this channel.

    • getPipeline

      ChannelPipeline getPipeline()
      Returns the ChannelPipeline which handles ChannelEvents associated with this channel.

    • isOpen

      boolean isOpen()
      Returns true if and only if this channel is open.

    • isBound

      boolean isBound()
      Returns true if and only if this channel is bound to a local address.

    • isConnected

      boolean isConnected()
      Returns true if and only if this channel is connected to a remote address.

    • getLocalAddress

      SocketAddress getLocalAddress()
      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.

    • getRemoteAddress

      SocketAddress getRemoteAddress()
      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 MessageEvent.getRemoteAddress() to determine the origination of the received message as this method will return null.

    • write

      ChannelFuture write(Object message)
      Sends a message to this channel asynchronously. If this channel was created by a connectionless transport (e.g. DatagramChannel) and is not connected yet, you have to call write(Object, SocketAddress) instead. Otherwise, the write request will fail with NotYetConnectedException and an 'exceptionCaught' event will be triggered.
      Parameters:
      message - the message to write
      Returns:
      the ChannelFuture which will be notified when the write request succeeds or fails
      Throws:
      NullPointerException - if the specified message is null

    • write

      ChannelFuture write(Object message, SocketAddress remoteAddress)
      Sends a message to this channel asynchronously. It has an additional parameter that allows a user to specify where to send the specified message instead of this channel's current remote address. If this channel was created by a connectionless transport (e.g. DatagramChannel) and is not connected yet, you must specify non-null address. Otherwise, the write request will fail with NotYetConnectedException and an 'exceptionCaught' event will be triggered.
      Parameters:
      message - the message to write
      remoteAddress - where to send the specified message. This method is identical to write(Object) if null is specified here.
      Returns:
      the ChannelFuture which will be notified when the write request succeeds or fails
      Throws:
      NullPointerException - if the specified message is null

    • bind

      ChannelFuture bind(SocketAddress localAddress)
      Binds this channel to the specified local address asynchronously.
      Parameters:
      localAddress - where to bind
      Returns:
      the ChannelFuture which will be notified when the bind request succeeds or fails
      Throws:
      NullPointerException - if the specified address is null

    • connect

      ChannelFuture connect(SocketAddress remoteAddress)
      Connects this channel to the specified remote address asynchronously.
      Parameters:
      remoteAddress - where to connect
      Returns:
      the ChannelFuture which will be notified when the connection request succeeds or fails
      Throws:
      NullPointerException - if the specified address is null

    • disconnect

      ChannelFuture disconnect()
      Disconnects this channel from the current remote address asynchronously.
      Returns:
      the ChannelFuture which will be notified when the disconnection request succeeds or fails

    • unbind

      ChannelFuture unbind()
      Unbinds this channel from the current local address asynchronously.
      Returns:
      the ChannelFuture which will be notified when the unbind request succeeds or fails

    • close

      ChannelFuture close()
      Closes this channel asynchronously. If this channel is bound or connected, it will be disconnected and unbound first. Once a channel is closed, it can not be open again. Calling this method on a closed channel has no effect. Please note that this method always returns the same future instance.
      Returns:
      the ChannelFuture which will be notified when the close request succeeds or fails

    • getCloseFuture

      ChannelFuture getCloseFuture()
      Returns the ChannelFuture which will be notified when this channel is closed. This method always returns the same future instance.

    • getInterestOps

      int getInterestOps()
      Returns the current interestOps of this channel.
      Returns:
      OP_NONE, OP_READ, OP_WRITE, or OP_READ_WRITE

    • isReadable

      boolean isReadable()
      Returns true if and only if the I/O thread will read a message from this channel. This method is a shortcut to the following code: 
       return (getInterestOps() invalid input: '&' OP_READ) != 0;

    • 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. This method is a shortcut to the following code: 
       return (getInterestOps() invalid input: '&' OP_WRITE) == 0;

    • setInterestOps

      ChannelFuture setInterestOps(int interestOps)
      Changes the interestOps of this channel asynchronously.
      Parameters:
      interestOps - the new interestOps
      Returns:
      the ChannelFuture which will be notified when the interestOps change request succeeds or fails

    • setReadable

      ChannelFuture setReadable(boolean readable)
      Suspends or resumes the read operation of the I/O thread asynchronously. This method is a shortcut to the following code: 
       int interestOps = getInterestOps();
 if (readable) {
     setInterestOps(interestOps | OP_READ);
 } else {
     setInterestOps(interestOps invalid input: '&' ~OP_READ);
 }
      Parameters:
      readable - true to resume the read operation and false to suspend the read operation
      Returns:
      the ChannelFuture which will be notified when the interestOps change request succeeds or fails

    • getUserDefinedWritability

      boolean getUserDefinedWritability(int index)
      Returns true if and only if the user-defined writability flag at the specified index is set to true.

    • setUserDefinedWritability

      void setUserDefinedWritability(int index, boolean isWritable)
      Sets a user-defined writability flag at the specified index.

    • getAttachment

      Object getAttachment()
      Retrieves an object which is attached to this Channel.
      Returns:
      null if no object was attached or null was attached

    • setAttachment

      void setAttachment(Object attachment)
      Attaches an object to this Channel to store a stateful information