?

http://linugb118.blog.51cto.com/272628/420738

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.連接server
ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port));

這里解釋一下channelFuture：

在Netty中所有的io操作都是異步的，這也就是意味任何io訪問，那么就立即返回處理，并且不能確保
返回的數據全部完成。因此就出現了channelFuture，channelFuture在傳輸數據時候包括數據和狀態兩個
部分。他只有Uncompleted和Completed

?
?*????????????????????????????????????? +---------------------------+
?*????????????????????????????????????? | Completed successfully??? |
?*????????????????????????????????????? +---------------------------+
?*???????????????????????????????? +---->????? isDone() = <b>true</b>????? |
?* +--------------------------+??? |??? |?? isSuccess() = <b>true</b>????? |
?* |??????? Uncompleted?????? |??? |??? +===========================+
?* +--------------------------+??? |??? | Completed with failure??? |
?* |????? isDone() = <b>false</b>??? |??? |??? +---------------------------+
?* |?? isSuccess() = false??? |----+---->?? isDone() = <b>true</b>???????? |
?* | isCancelled() = false??? |??? |??? | getCause() = <b>non-null</b>???? |
?* |??? getCause() = null???? |??? |??? +===========================+
?* +--------------------------+??? |??? | Completed by cancellation |
?*???????????????????????????????? |??? +---------------------------+
?*???????????????????????????????? +---->????? isDone() = <b>true</b>????? |
?*????????????????????????????????????? | isCancelled() = <b>true</b>????? |
?*????????????????????????????????????? +---------------------------+
?
?既然netty io是異步的，那么如何知道channel傳送完成有兩種方式，一種添加監聽器
?addListener(ChannelFutureListener) 還有一種直接調用await()方法，這兩種方式
?有下面的區別
?監聽器：是以事件模式的，因此代碼就需要用事件模式的樣式去寫，相當復雜，但他是non-blocking模式的
?性能方面要比await方法好，而且不會產生死鎖情況
?
?await(): 直接方法調用，使用簡單，但是他是blocking模式，性能方面要弱而且會產生死鎖情況
?
?不要在ChannelHandler 里面調用await(),這是因為通常在channelHandler里的event method是被i/o線程調用的
?（除非ChannelPipeline里面有個ExecutionHandler），那么如果這個時候用await就容易產生死鎖。
?
?錯誤樣例：
?// BAD - NEVER DO THIS
?* {@code @Override}
?* public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
?*???? if (e.getMessage() instanceof GoodByeMessage) {
?*???????? {@link ChannelFuture} future = e.getChannel().close();
?*???????? future.awaitUninterruptibly();
?*???????? // Perform post-closure operation
?*???????? // ...
?*???? }
?* }
?*
?正確樣例：
?* // GOOD
?* {@code @Override}
?* public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
?*???? if (e.getMessage() instanceof GoodByeMessage) {
?*???????? {@link ChannelFuture} future = e.getChannel().close();
?*???????? future.addListener(new {@link ChannelFutureListener}() {
?*???????????? public void operationComplete({@link ChannelFuture} future) {
?*???????????????? // Perform post-closure operation
?*???????????????? // ...
?*???????????? }
?*???????? });
?*???? }
?* }
?
?雖然await調用比較危險，但是你確保不是在一個i/o 線程中調用該方法，畢竟await方法還是很簡潔方便的，如果
?調用該方法是在一個i/o 線程，那么就會拋出 IllegalStateException
?
?await的timeout和i/o timeout區別
?需要注意的是這兩個timeout是不一樣的， #await(long)，#await(long, TimeUnit), #awaitUninterruptibly(long),
?#awaitUninterruptibly(long, TimeUnit) 這里面的timeout也i/o timeout 沒有任何關系，如果io timeout，那么
?channelFuture 將被標記為completed with failure，而await的timeout 與future完全沒有關系，只是await動作的
?timeout。
?錯誤代碼
? * // BAD - NEVER DO THIS
?* {@link ClientBootstrap} b = ...;
?* {@link 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
?* }
?*
?正確代碼
?* // GOOD
?* {@link ClientBootstrap} b = ...;
?* // Configure the connect timeout option.
?* <b>b.setOption("connectTimeoutMillis", 10000);</b>
?* {@link 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.等待或監聽數據全部完成
如： future.getChannel().getCloseFuture().awaitUninterruptibly();

5.釋放連接等資源
?bootstrap.releaseExternalResources();
?
Server：
1.配置server

ServerBootstrap bootstrap = new ServerBootstrap(
??????????????? new NioServerSocketChannelFactory(
??????????????????????? Executors.newCachedThreadPool(),
??????????????????????? Executors.newCachedThreadPool()));
???????????????????????
2.設置pipeFactory
??????? bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
??????????? public ChannelPipeline getPipeline() throws Exception {
??????????????? return Channels.pipeline(new EchoServerHandler());
??????????? }
??????? });
??? 或者
?? bootstrap.setPipelineFactory(new HttpServerPipelineFactory());
??
3.綁定sever端端口
bootstrap.bind(new InetSocketAddress(8080));

?

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