ChannelEvent是和这个Channel相关的IO事件和请求，会由各个ChannelHandler来处理。
事件分为上行（Upstream）和下行（Downstream）两种。
当服务器从客户端收到一个消息，那么与之相关的就是一个上行事件（Upstream Event），流水线（Pipeline）中的UpstreamChannelHandler会处理它；如果服务器要响应这个客户端，那么与响应消息对应的就是下行事件（Downstream Event），流水线（Pipeline）中的DownstreamChannelHandler会处理它。
org.jboss.netty.channel.ChannelEvent源码：
public interface ChannelEvent {
/**
* Returns the {@link Channel} which is associated with this event.
*/
Channel getChannel();
/**
* Returns the {@link ChannelFuture} which is associated with this event.
* If this event is an upstream event, this method will always return a
* {@link 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.
*/
ChannelFuture getFuture();
}
An I/O event or I/O request associated with a Channel.
A ChannelEvent is handled by a series of ChannelHandlers 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 |
| "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 |
| "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 |
| "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. |
网友评论