org.jboss.netty.channel

## Interface ChannelEvent

All Known Subinterfaces:
  ChannelStateEvent, ChildChannelStateEvent, ExceptionEvent, IdleStateEvent, MessageEvent, WriteCompletionEvent

All Known Implementing Classes:
  DefaultChildChannelStateEvent, DefaultExceptionEvent, DefaultIdleStateEvent, DefaultWriteCompletionEvent, DownstreamChannelStateEvent, DownstreamMessageEvent, UpstreamChannelStateEvent, UpstreamMessageEvent

    public interface ChannelEvent

An I/O event or I/O request associated with a `Channel`.

A `ChannelEvent` is handled by a series of `ChannelHandler`s in a `ChannelPipeline`.

### Upstream events and downstream events, and their interpretation

Every event is either an upstream event or a downstream event. If an event flows forward from the first handler to the last handler in a `ChannelPipeline`, we call it an upstream event and say "an event goes upstream." If an event flows backward from the last handler to the first handler in a `ChannelPipeline`, we call it a downstream event and say "an event goes downstream." (Please refer to the diagram in `ChannelPipeline` for more explanation.)

When your server receives a message from a client, the event associated with the received message is an upstream event. When your server sends a message or reply to the client, the event associated with the write request is a downstream event. The same rule applies for the client side. If your client sent a request to the server, it means your client triggered a downstream event. If your client received a response from the server, it means your client will be notified with an upstream event. Upstream events are often the result of inbound operations such as `InputStream.read(byte[])`, and downstream events are the request for outbound operations such as `OutputStream.write(byte[])`, `Socket.connect(SocketAddress)`, and `Socket.close()`.

#### Upstream events

Event name | Event type and condition | Meaning
--- | --- | ---
`"messageReceived"` | `MessageEvent` | a message object (e.g. `ChannelBuffer`) was received from a remote peer
`"exceptionCaught"` | `ExceptionEvent` | an exception was raised by an I/O thread or a `ChannelHandler`
`"channelOpen"` | `ChannelStateEvent` (state = `OPEN`, value = `true`) | a `Channel` is open, but not bound nor connected | Be aware that this event is fired from within the Boss-Thread so you should not execute any heavy operation in there as it will block the dispatching to other workers!
`"channelClosed"` | `ChannelStateEvent` (state = `OPEN`, value = `false`) | a `Channel` was closed and all its related resources were released
`"channelBound"` | `ChannelStateEvent` (state = `BOUND`, value = `SocketAddress`) | a `Channel` is open and bound to a local address, but not connected. | Be aware that this event is fired from within the Boss-Thread so you should not execute any heavy operation in there as it will block the dispatching to other workers!
`"channelUnbound"` | `ChannelStateEvent` (state = `BOUND`, value = `null`) | a `Channel` was unbound from the current local address
`"channelConnected"` | `ChannelStateEvent` (state = `CONNECTED`, value = `SocketAddress`) | a `Channel` is open, bound to a local address, and connected to a remote address | Be aware that this event is fired from within the Boss-Thread so you should not execute any heavy operation in there as it will block the dispatching to other workers!
`"writeComplete"` | `WriteCompletionEvent` | something has been written to a remote peer
`"channelDisconnected"` | `ChannelStateEvent` (state = `CONNECTED`, value = `null`) | a `Channel` was disconnected from its remote peer
`"channelInterestChanged"` | `ChannelStateEvent` (state = `INTEREST_OPS`, no value) | a `Channel`'s `interestOps` was changed

These two additional event types are used only for a parent channel which can have a child channel (e.g. `ServerSocketChannel`).

Event name | Event type and condition | Meaning
--- | --- | ---
`"childChannelOpen"` | `ChildChannelStateEvent` (`childChannel.isOpen() = true`) | a child `Channel` was open (e.g. a server channel accepted a connection.)
`"childChannelClosed"` | `ChildChannelStateEvent` (`childChannel.isOpen() = false`) | a child `Channel` was closed (e.g. the accepted connection was closed.)

#### Downstream events

Event name | Event type and condition | Meaning
--- | --- | ---
`"write"` | `MessageEvent` | Send a message to the `Channel`.
`"bind"` | `ChannelStateEvent` (state = `BOUND`, value = `SocketAddress`) | Bind the `Channel` to the specified local address.
`"unbind"` | `ChannelStateEvent` (state = `BOUND`, value = `null`) | Unbind the `Channel` from the current local address.
`"connect"` | `ChannelStateEvent` (state = `CONNECTED`, value = `SocketAddress`) | Connect the `Channel` to the specified remote address.
`"disconnect"` | `ChannelStateEvent` (state = `CONNECTED`, value = `null`) | Disconnect the `Channel` from the current remote address.
`"close"` | `ChannelStateEvent` (state = `OPEN`, value = `false`) | Close the `Channel`.

Other event types and conditions which were not addressed here will be ignored and discarded. Please note that there's no `"open"` in the table. It is because a `Channel` is always open when it is created by a `ChannelFactory`.

### Additional resources worth reading

Please refer to the `ChannelHandler` and `ChannelPipeline` documentation to find out how an event flows in a pipeline and how to handle the event in your application.

### Method Summary

Methods
`Channel` `getChannel()` Returns the `Channel` which is associated with this event.
`ChannelFuture` `getFuture()` Returns the `ChannelFuture` which is associated with this event.

### Method Detail

#### getChannel

    Channel getChannel()

Returns the `Channel` which is associated with this event.

#### getFuture

    ChannelFuture getFuture()

Returns the `ChannelFuture` which is associated with this event. If this event is an upstream event, this method will always return a `SucceededChannelFuture` because the event has occurred already. If this event is a downstream event (i.e. I/O request), the returned future will be notified when the I/O request succeeds or fails.