Netty 是JBoss旗下的io传输的框架,他利用java里面的nio来实现高效,稳定的io传输。
作为io传输,就会有client和server,下面我们看看用netty怎样写client和server
Client:
需要做的事情:
1.配置client启动类
ClientBootstrap bootstrap = new ClientBootstrap(..)
2.根据不同的协议或者模式为client启动类设置pipelineFactory。
这里telnet pipline Factory 在netty中已经存在,所有直接用
bootstrap.setPipelineFactory(new TelnetClientPipelineFactory());
也可以自己定义
bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(
new DiscardClientHandler(firstMessageSize));
}
});
这里DiscardClientHandler 就是自己定义的handler,他需要
public class DiscardServerHandler extends SimpleChannelUpstreamHandler
继承SimpleChannelUpstreamHandler 来实现自己的handler。这里DiscardClientHandler
是处理自己的client端的channel,他的
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
// Server is supposed to send nothing. Therefore, do nothing.
}
可以看到Discard client不需要接受任何信息
3.连接server
ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port));
这里解释一下channelFuture:
在Netty中所有的io操作都是异步的,这也就是意味任何io访问,那么就立即返回处理,并且不能确保
返回的数据全部完成。因此就出现了channelFuture,channelFuture在传输数据时候包括数据和状态两个
部分。他只有Uncompleted和Completed
+---------------------------+ | Completed successfully | +---------------------------+ +----> isDone() = true | +--------------------------+ | | isSuccess() = true | | Uncompleted | | +===========================+ +--------------------------+ | | Completed with failure | | isDone() = false | | +---------------------------+ | isSuccess() = false |----+----> isDone() = true | | isCancelled() = false | | | getCause() = non-null | | getCause() = null | | +===========================+ +--------------------------+ | | Completed by cancellation | | +---------------------------+ +----> isDone() = true | | isCancelled() = true | +---------------------------+
既然netty io是异步的,那么如何知道channel传送完成有两种方式,一种添加监听器
addListener(ChannelFutureListener) 还有一种直接调用await()方法,这两种方式
有下面的区别
监听器:是以事件模式的,因此代码就需要用事件模式的样式去写,相当复杂,但他是non-blocking模式的
性能方面要比await方法好,而且不会产生死锁情况
await(): 直接方法调用,使用简单,但是他是blocking模式,性能方面要弱而且会产生死锁情况
不要在ChannelHandler 里面调用await(),这是因为通常在channelHandler里的event method是被i/o线程调用的
(除非ChannelPipeline里面有个ExecutionHandler),那么如果这个时候用await就容易产生死锁。
// BAD - NEVER DO THIS@Override
public void messageReceived(ChannelHandlerContext
ctx,MessageEvent
e) { if (e.getMessage() instanceof GoodByeMessage) {ChannelFuture
future = e.getChannel().close(); future.awaitUninterruptibly(); // Perform post-closure operation // ... } } // GOOD@Override
public void messageReceived(ChannelHandlerContext
ctx,MessageEvent
e) { if (e.getMessage() instanceof GoodByeMessage) {ChannelFuture
future = e.getChannel().close(); future.addListener(newChannelFutureListener
() { public void operationComplete(ChannelFuture
future) { // Perform post-closure operation // ... } }); } }
虽然await调用比较危险,但是你确保不是在一个i/o 线程中调用该方法,毕竟await方法还是很简洁方便的,如果
调用该方法是在一个i/o 线程,那么就会抛出 IllegalStateException
await的timeout和i/o timeout区别
需要注意的是这两个timeout是不一样的, #await(long),#await(long, TimeUnit), #awaitUninterruptibly(long),
#awaitUninterruptibly(long, TimeUnit) 这里面的timeout也i/o timeout 没有任何关系,如果io timeout,那么
channelFuture 将被标记为completed with failure,而await的timeout 与future完全没有关系,只是await动作的
timeout。
// BAD - NEVER DO THISClientBootstrap
b = ...;ChannelFuture
f = b.connect(...); f.awaitUninterruptibly(10, TimeUnit.SECONDS); if (f.isCancelled()) { // Connection attempt cancelled by user } else if (!f.isSuccess()) { // You might get a NullPointerException here because the future // might not be completed yet. f.getCause().printStackTrace(); } else { // Connection established successfully } // GOODClientBootstrap
b = ...; // Configure the connect timeout option. b.setOption("connectTimeoutMillis", 10000);ChannelFuture
f = b.connect(...); f.awaitUninterruptibly(); // Now we are sure the future is completed. assert f.isDone(); if (f.isCancelled()) { // Connection attempt cancelled by user } else if (!f.isSuccess()) { f.getCause().printStackTrace(); } else { // Connection established successfully }
4.等待或监听数据全部完成
如: future.getChannel().getCloseFuture().awaitUninterruptibly();
5.释放连接等资源
bootstrap.releaseExternalResources();
Server:
1.配置server
ServerBootstrap bootstrap = new ServerBootstrap(
new NioServerSocketChannelFactory(
Executors.newCachedThreadPool(),
Executors.newCachedThreadPool()));
2.设置pipeFactory
bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(new EchoServerHandler());
}
});
或者
bootstrap.setPipelineFactory(new HttpServerPipelineFactory());
3.绑定sever端端口
bootstrap.bind(new InetSocketAddress(8080));