锐客网

  1. 首页 > it技术 > >

Netty应用


目前网上我没有看到让我觉得满意的文章，netty实战这本书很多东西也是一笔带过，并没有做详细的解释，很多东西只有靠自己测试，本文不会详细的介绍各种概念，建议先看netty实战。本文的目的是解释我自己在学习过程的一些疑惑。
Netty主要包含channel, 回调，Future，事件驱动及channelhandler.
回调的概念就是当你触发了某个事件，然后就自动调用相应的方法，比如JAVA SWING， 当你点击某个按钮，那就触发了按钮的事件，然后去调用相应的方法。
Future属于多线程里面的，线程启动然后执行，你并不能控制它什么时候结束，比如A线程启动，计算一个结果，主函数main希望获得A线程的结果，你可以通过Thread.join方式等待A执行完，再执行主方法，这种方式效率太低，因此出现了future，把线程放在future task里面执行，主函数继续运行，然后通过future.get方式获得结果，如果线程还没有执行完，会堵塞，直到完成。如果已经完成，那么通过get直接获得结果。
事件驱动就是触发了某个事件，这个和回调相结合，比如channelactive方法，当客户端连接到服务端，就会触发建立一条通道channel的事件, 这个时候channelactive就被调用了。
channelHandler顾名思义是拦截器，用来处理通道的数据的东西， channelhandler分in和out，对于客户端来说，进入客户端的数据就叫入站，数据传输到服务端就叫出站，对于服务端来说概念一样。
先来看一个示例：客户端连接到服务端发送Netty Rocks, 服务端收到信息打印出来，再发送welcome client给客户端
ServerHandler

package com.isesol.log.log; import java.net.InetAddress; import java.util.ArrayList; import java.util.Date; import java.util.List; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.Channel; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelFutureListener; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; import io.netty.channel.SimpleChannelInboundHandler; import io.netty.channel.ChannelHandler; import io.netty.channel.ChannelHandler.Sharable; import io.netty.handler.codec.string.StringDecoder; import io.netty.handler.codec.string.StringEncoder; import io.netty.util.CharsetUtil; @Sharable public class ServerHandler extends SimpleChannelInboundHandler { @Override public void channelReadComplete(ChannelHandlerContext ctx) { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { cause.printStackTrace(); ctx.close(); } @Override protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception { // TODO Auto-generated method stubSystem.out.println(msg.toString(CharsetUtil.UTF_8)); ChannelFuture future = ctx.write(Unpooled.copiedBuffer("welcome client!",CharsetUtil.UTF_8)); // ChannelFuture future = ctx.write(Unpooled.copiedBuffer("welcomee Client", CharsetUtil.UTF_8)); }}

Server:
package com.isesol.log.log; import io.netty.bootstrap.ServerBootstrap; import io.netty.channel.ChannelInitializer; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioServerSocketChannel; import io.netty.handler.codec.DelimiterBasedFrameDecoder; import io.netty.handler.codec.Delimiters; import io.netty.handler.codec.string.StringDecoder; import io.netty.handler.codec.string.StringEncoder; import io.netty.handler.logging.LogLevel; import io.netty.handler.logging.LoggingHandler; public class Server { private static final StringDecoder DECODER = new StringDecoder(); private static final StringEncoder ENCODER = new StringEncoder(); public static void main(String[] args) throws InterruptedException {//服务端有2个EventLoopGroup, 一个服务于自己，一个服务客户端， 也可以只用一个EventLoopGroup EventLoopGroup bossGroup = new NioEventLoopGroup(1); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { ServerBootstrap b = new ServerBootstrap(); b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class) //指定channel格式 .handler(new LoggingHandler(LogLevel.INFO)).childHandler(new ChannelInitializer() {@Override public void initChannel(SocketChannel ch) throws Exception { //ch.pipeline().addLast(new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter())); // ch.pipeline().addLast(DECODER); // ch.pipeline().addLast(ENCODER); // ch.pipeline().addLast(new ServerHandler2()); //添加了一个handler,用来处理通道数据 ch.pipeline().addLast(new ServerHandler()); }}); b.bind(8092).sync().channel().closeFuture().sync(); } finally { bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } }}

ClientHandler
package com.isesol.log.log; import java.net.InetAddress; import java.nio.charset.Charset; import java.util.Date; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; import io.netty.channel.SimpleChannelInboundHandler; import io.netty.channel.ChannelHandler.Sharable; import io.netty.util.CharsetUtil; @Sharable public class ClientHandler extends SimpleChannelInboundHandler { @Override public void channelActive(ChannelHandlerContext ctx) throws Exception {ctx.write(Unpooled.copiedBuffer("Netty Rocks", CharsetUtil.UTF_8)); ctx.flush(); } @Override public void channelReadComplete(ChannelHandlerContext ctx) { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { cause.printStackTrace(); ctx.close(); } @Override protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception { // TODO Auto-generated method stubSystem.out.println(msg.toString(CharsetUtil.UTF_8)); }}

Client:
package com.isesol.log.log; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import io.netty.bootstrap.Bootstrap; import io.netty.buffer.Unpooled; import io.netty.channel.Channel; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelInitializer; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioSocketChannel; import io.netty.handler.codec.DelimiterBasedFrameDecoder; import io.netty.handler.codec.Delimiters; import io.netty.handler.codec.string.StringDecoder; import io.netty.handler.codec.string.StringEncoder; import io.netty.util.CharsetUtil; public class Client { private static final StringDecoder DECODER = new StringDecoder(); private static final StringEncoder ENCODER = new StringEncoder(); public static void main(String[] args) throws InterruptedException, IOException {EventLoopGroup group = new NioEventLoopGroup(); try { Bootstrap b = new Bootstrap(); b.group(group).channel(NioSocketChannel.class).handler(new ChannelInitializer() {@Override public void initChannel(SocketChannel ch) throws Exception { // ch.pipeline().addLast(new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter())); // ch.pipeline().addLast(DECODER); //ch.pipeline().addLast(ENCODER); ch.pipeline().addLast(new ClientHandler()); }}); ; // Start the connection attempt. Channel ch = b.connect("127.0.0.1", 8092).sync().channel(); // Read commands from the stdin. ChannelFuture lastWriteFuture = null; BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); for (; ; ) { String line = in.readLine(); if (line == null) { break; }// Sends the received line to the server. lastWriteFuture = ch.writeAndFlush(Unpooled.copiedBuffer(line,CharsetUtil.UTF_8)); // If user typed the 'bye' command, wait until the server closes // the connection. if ("bye".equals(line.toLowerCase())) { ch.closeFuture().sync(); break; } }// Wait until all messages are flushed before closing the channel. if (lastWriteFuture != null) { lastWriteFuture.sync(); } } finally { group.shutdownGracefully(); } }}

然后打包成JAR，执行结果如下：
[root@datanode01-ucloud ~]# hadoop jar server.jar 18/08/21 01:38:50 INFO logging.LoggingHandler: [id: 0x4d2022aa] REGISTERED 18/08/21 01:38:50 INFO logging.LoggingHandler: [id: 0x4d2022aa] BIND(0.0.0.0/0.0.0.0:8092) 18/08/21 01:38:50 INFO logging.LoggingHandler: [id: 0x4d2022aa, /0.0.0.0:8092] ACTIVE 18/08/21 01:38:55 INFO logging.LoggingHandler: [id: 0x4d2022aa, /0.0.0.0:8092] RECEIVED: [id: 0xdd0eafe7, /127.0.0.1:36936 => /127.0.0.1:8092] its going to handler 1 Netty Rocks

[root@datanode01-ucloud ~]# hadoop jar client.jar welcome client!

【Netty应用】ChannelPipeline 和ChannelHandler的关系：
服务端与客户端连接之后，会建立一个通道channel, 数据的传输就是通过ChannelPipeline, ChannelHandler就是挂在ChannelPipeline拦截器，用来处理数据，分入站和出站。你可以在ChannelPipeline上挂无数个ChannelHandler，也可以一个不挂。把ChannelPipeline想象成一条水管，然后水管上有很多水龙头，水缓缓的从水管流入或者流出，每个水龙头作为一个拦截器，用来处理这些水。
Netty应用
文章图片

inboundhandler的执行顺序是从左到右，outbound是从右到左，在添加handler到pipeline的时候，顺序非常重要。下面是先执行ENcoder， 再执行DiscardHandle。
ch.pipeline() .addLast(new StringEncoder(CharsetUtil.UTF_8)) .addLast(new DiscardHandle());

outboundhandler的执行顺序相反，先从尾端处理，假设上面的2个handler属于outbound，那么处理顺序是DiscardHandle再StringEncoder.
最简单的理解就是 inbound 是从头到尾，outbound是从尾到头，addlast的意思添加到最后的意思，上面添加了2次，很显然stringencoder在前面，而对于outbound来说，DiscardHandler是最后，属于尾端，先执行。

Encoder和Deconder:
网络数据传输的单位是字节，ByteBuf是数据的容器，如果你发送的数据本身就是字节类型，那么是不需要encoder和decoder的，从上面的示例可以看到，我并没有添加任何encoder和decoder channelhandler，但是当你发送的数据类型不是字节，那么就一定要使用encoder和decoder， 否者服务端或者客户端是无法读取你的数据。网络传输还涉及到半包，粘包的概念，这个建议参考专门的文章。
@Sharable public class DiscardClient extends SimpleChannelInboundHandler { @Override public void channelActive(ChannelHandlerContext ctx) { ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!", CharsetUtil.UTF_8)); } }

上面的SimpleChannelInboundHandler表示数据传输是ByteBuf，因此在ctx.writeAndFlush的时候以ByteBuf的方式发送数据。现在我来修改成以String发送数据，这个时候你就会需要Encoder/Decoder，encoder的概念是把Sting包装成 ByteBuf再发送, Decoder接受到ByteBuf再解码成String. 如果没有这2个动作，你是无法发送数据和接受数据的，上面已经解释了，网络数据传输一定是字节。
修改inbound为String，发送数据的时候直接以String发送：
package com.isesol.elasticsearch; import java.nio.charset.Charset; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelFutureListener; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; import io.netty.channel.SimpleChannelInboundHandler; import io.netty.util.CharsetUtil; import io.netty.util.ReferenceCountUtil; import io.netty.channel.ChannelHandler.Sharable; @Sharable public class DiscardHandle extends SimpleChannelInboundHandler { @Override public void channelReadComplete(ChannelHandlerContext ctx) { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { super.exceptionCaught(ctx, cause); ctx.close(); } @Override protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception { // TODO Auto-generated method stub System.out.println(msg); ctx.writeAndFlush(msg); }}

那么在添加handler的时候就必须要添加encoder:
try{ ServerBootstrap bootstrap = new ServerBootstrap(); bootstrap.group(boss,worker).channel(NioServerSocketChannel.class) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer() { @Override public void initChannel(SocketChannel ch) throws Exception { ch.pipeline() .addLast(new StringEncoder(CharsetUtil.UTF_8)) .addLast(new StringDecoder(CharsetUtil.UTF_8)) .addLast(new DiscardHandle()); } });

发送数据的时候先通过encoder把 String封装成ByteBuf，Decoder把接受进来的ByteBuf解码成String再打印。
去掉encoder handler来看一下实际结果，服务端收到了Netty rocks, 但是客户端什么也没有输出，按照规则应该输出服务端发送的数据，这就是因为没有encoder string为ByteBuf，导致数据根本发不了：
[root@datanode01-ucloud ~]# [root@datanode01-ucloud ~]# hadoop jar service.jar 18/08/21 10:52:58 INFO logging.LoggingHandler: [id: 0x6022f658] REGISTERED 18/08/21 10:52:58 INFO logging.LoggingHandler: [id: 0x6022f658] BIND(/127.0.0.1:8888) 18/08/21 10:52:58 INFO logging.LoggingHandler: [id: 0x6022f658, /127.0.0.1:8888] ACTIVE 18/08/21 10:53:01 INFO logging.LoggingHandler: [id: 0x6022f658, /127.0.0.1:8888] RECEIVED: [id: 0x703db179, /127.0.0.1:56146 => /127.0.0.1:8888] Netty rocks!

^C[root@datanode01-ucloud ~]# hadoop jar client.jar

疑问1：之前不是说inbound会按照添加的handler顺序处理数据吗？那我通过DiscardHandler发送数据，怎么还会执行Encoder ？ 顺序明明是 encoder, decoder, discardhandler.
为了证明到底是否执行了encoder, decoder,我们需要做一个实验，StringEncoder, StringDecoder是netty提供的，我们把它们拷贝到自己的类中，然后在构造函数添加一个打印，一旦调用了这2个handler，就肯定会打印数据。 这2个类名字取为myStringEncoder, myStringDecoder， 测试2种情况，只发不收和只收不发，这样才知道整个过程是怎么样：
package com.isesol.elasticsearch; import io.netty.buffer.ByteBuf; import io.netty.buffer.ByteBufUtil; import io.netty.channel.ChannelHandler.Sharable; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelPipeline; import io.netty.handler.codec.LineBasedFrameDecoder; import io.netty.handler.codec.MessageToMessageEncoder; import java.nio.CharBuffer; import java.nio.charset.Charset; import java.util.List; @Sharable public class myStringEncoder extends MessageToMessageEncoder{ // TODO Use CharsetEncoder instead. private final Charset charset; /** * Creates a new instance with the current system character set. */ public myStringEncoder() { this(Charset.defaultCharset()); }/** * Creates a new instance with the specified character set. */ public myStringEncoder(Charset charset) {System.out.println("invoker encoder"); if (charset == null) { throw new NullPointerException("charset"); } this.charset = charset; }@Override protected void encode(ChannelHandlerContext ctx, CharSequence msg, List out) throws Exception { if (msg.length() == 0) { return; }System.out.println("start to encoder!!"); out.add(ByteBufUtil.encodeString(ctx.alloc(), CharBuffer.wrap(msg), charset)); }}
package com.isesol.elasticsearch; import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandler.Sharable; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelPipeline; import io.netty.handler.codec.ByteToMessageDecoder; import io.netty.handler.codec.DelimiterBasedFrameDecoder; import io.netty.handler.codec.LineBasedFrameDecoder; import io.netty.handler.codec.MessageToMessageDecoder; import java.nio.charset.Charset; import java.util.List; public class myStringDecoder extends MessageToMessageDecoder {private final Charset charset; /** * Creates a new instance with the current system character set. */ public myStringDecoder() { this(Charset.defaultCharset()); }/** * Creates a new instance with the specified character set. */ public myStringDecoder(Charset charset) {System.out.println("Decoder invoke"); if (charset == null) { throw new NullPointerException("charset"); } this.charset = charset; }@Override protected void decode(ChannelHandlerContext ctx, ByteBuf msg, List out) throws Exception { System.out.println("start to decoder!!"); out.add(msg.toString(charset)); } }
try{ ServerBootstrap bootstrap = new ServerBootstrap(); bootstrap.group(boss,worker).channel(NioServerSocketChannel.class) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer() { @Override public void initChannel(SocketChannel ch) throws Exception { ch.pipeline() .addLast(new myStringEncoder(CharsetUtil.UTF_8)) .addLast(new myStringDecoder(CharsetUtil.UTF_8)) .addLast(new DiscardHandle()); } });

只发不收：
[root@datanode01-ucloud ~]# hadoop jar service.jar 18/08/21 11:58:39 INFO logging.LoggingHandler: [id: 0xa212be6f] REGISTERED 18/08/21 11:58:39 INFO logging.LoggingHandler: [id: 0xa212be6f] BIND(/127.0.0.1:8888) 18/08/21 11:58:39 INFO logging.LoggingHandler: [id: 0xa212be6f, /127.0.0.1:8888] ACTIVE 18/08/21 11:58:43 INFO logging.LoggingHandler: [id: 0xa212be6f, /127.0.0.1:8888] RECEIVED: [id: 0x5a6bb294, /127.0.0.1:33552 => /127.0.0.1:8888] invoker encoder Decoder invoke DiscardHandler invoke start to encoder!!

^C[root@datanode01-ucloud ~]# hadoop jar client.jar Client received: this is from SERVER

从server端的调用顺序先encoder,再decoder,再执行DiscardHandler，发送的时候执行封装（start to encoder)。注意一点，虽然调用了decoder handler，但实际上没有去执行decoder的解码动作。
只收不发：
[root@datanode01-ucloud ~]# hadoop jar service.jar 18/08/21 12:06:15 INFO logging.LoggingHandler: [id: 0xb7f24453] REGISTERED 18/08/21 12:06:15 INFO logging.LoggingHandler: [id: 0xb7f24453] BIND(/127.0.0.1:8888) 18/08/21 12:06:15 INFO logging.LoggingHandler: [id: 0xb7f24453, /127.0.0.1:8888] ACTIVE 18/08/21 12:06:18 INFO logging.LoggingHandler: [id: 0xb7f24453, /127.0.0.1:8888] RECEIVED: [id: 0x86bc1f79, /127.0.0.1:37392 => /127.0.0.1:8888] invoker encoder Decoder invoke DiscardHandler invoke start to decoder!! Netty rocks!

调用顺序还是保持不变，最后执行decoder解码。
最后一个疑问，发数据的时候虽然掉用了decoder，但实际没有执行解码动作，收数据调用了encoder，也没有进行编码动作，这是为什么？ 谁在背后操纵？ 个人理解调用handler的时候会全部启动，但是至于执行不执行看实际逻辑，如果是进来的数据，很显然不需要encoder，那么就不会去执行。
Encode from one message to an other. This method will be called for each written message that can be handled by this encoder.

疑问2：之前我们提过入站inbound ,出站为outbound, 我之前以为出去的数据必须经过 outbound，但是上面的示例中并没有添加outbound, 数据照样能够发送, 网上也有人问inbound 和outbound到底有什么区别?
在上面的基本概念中我提过，pipeline上可以挂无数个handler，也可以一个不挂。 handler仅仅是拦截器，需要就挂上去，不需要就不挂，发送和接收数据与handler毫无关系。就好比水管上的水龙头，水要流入或者流出，与水龙头本身没有关系，仅仅是你需要去控制水流的时候才把水龙头挂到水管上。
我们来建立一个outbound，看看添加了outbound会如何？
package com.isesol.elasticsearch; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelOutboundHandlerAdapter; import io.netty.channel.ChannelPromise; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandler.Sharable; @Sharable public class DiscardOutHandler extends ChannelOutboundHandlerAdapter { @Override public void read(ChannelHandlerContext ctx) throws Exception {System.out.println("DiscardOutHandler has been invoker!!"); ctx.read(); }@Override public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception { ctx.writeAndFlush((ByteBuf) msg, promise); }}

try { final Bootstrap b = new Bootstrap(); b.group(boss).channel(NioSocketChannel.class) .handler(new ChannelInitializer() { @Override public void initChannel(SocketChannel ch) throws Exception { ch.pipeline() .addLast(new DiscardClient()) .addLast(new DiscardOutHandler()); }});

测试结果：
[root@datanode01-ucloud ~]# hadoop jar service.jar 18/08/21 12:25:54 INFO logging.LoggingHandler: [id: 0x9f697a1d] REGISTERED 18/08/21 12:25:54 INFO logging.LoggingHandler: [id: 0x9f697a1d] BIND(/127.0.0.1:8888) 18/08/21 12:25:54 INFO logging.LoggingHandler: [id: 0x9f697a1d, /127.0.0.1:8888] ACTIVE 18/08/21 12:25:59 INFO logging.LoggingHandler: [id: 0x9f697a1d, /127.0.0.1:8888] RECEIVED: [id: 0x20c8a8aa, /127.0.0.1:47458 => /127.0.0.1:8888] invoker encoder Decoder invoke DiscardHandler invoke start to decoder!! Netty rocks!

[root@datanode01-ucloud ~]# [root@datanode01-ucloud ~]# hadoop jar client.jar DiscardOutHandler has been invoker!!

从上面图片看到，添加了outbound的后，确实调用了，只不过我这个outbound没有做任何处理，仅仅是ctx.read, 仅仅是forware to the next ChannelOutboundler。看具体含义;
Calls ChannelHandlerContext.read() to forward to the next ChannelOutboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.

我们再来做一个实验，客户端在inbound里面执行ctx.writeandflush，发送Netty rocks经过了outbound再出去，我们在outbound来修改要发送的数据，修改了2个方法：
package com.isesol.elasticsearch; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelOutboundHandlerAdapter; import io.netty.channel.ChannelPromise; import io.netty.util.CharsetUtil; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandler.Sharable; @Sharable public class DiscardOutHandler extends ChannelOutboundHandlerAdapter { @Override public void read(ChannelHandlerContext ctx) throws Exception {System.out.println("DiscardOutHandler has been invoker!!"); ctx.writeAndFlush(Unpooled.copiedBuffer("hello world", CharsetUtil.UTF_8)); }@Override public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception { ctx.write(Unpooled.copiedBuffer("dogshit!!", CharsetUtil.UTF_8), promise); }}

实验结果，服务端不仅收到了Netty rocks, 还收到了outbound 发送的hello world：
[root@datanode01-ucloud ~]# hadoop jar service.jar 18/08/21 12:49:31 INFO logging.LoggingHandler: [id: 0x53b17dcf] REGISTERED 18/08/21 12:49:31 INFO logging.LoggingHandler: [id: 0x53b17dcf] BIND(/127.0.0.1:8888) 18/08/21 12:49:31 INFO logging.LoggingHandler: [id: 0x53b17dcf, /127.0.0.1:8888] ACTIVE 18/08/21 12:49:36 INFO logging.LoggingHandler: [id: 0x53b17dcf, /127.0.0.1:8888] RECEIVED: [id: 0x60c153f4, /127.0.0.1:59732 => /127.0.0.1:8888] invoker encoder Decoder invoke DiscardHandler invoke start to decoder!! Netty rocks!hello world

[root@datanode01-ucloud ~]# hadoop jar client.jar DiscardOutHandler has been invoker!!

上面已经介绍了数据传输，编码解码，channelhandler，channelpipeline等主要的netty结构。还有一个future没有讲，我们随便在服务端或者客户端添加一个listener，用来监听动作是否成功失败。修改DiscardClient:
package com.isesol.elasticsearch; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.SimpleChannelInboundHandler; import io.netty.util.CharsetUtil; import io.netty.util.ReferenceCountUtil; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelFutureListener; import io.netty.channel.ChannelHandler.Sharable; @Sharable public class DiscardClient extends SimpleChannelInboundHandler { @Override public void channelActive(ChannelHandlerContext ctx) { ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!", CharsetUtil.UTF_8)).addListener(listener); } @Override public void channelRead0(ChannelHandlerContext ctx, ByteBuf in) { System.out.println("Client received: " + in.toString(CharsetUtil.UTF_8)); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { super.exceptionCaught(ctx, cause); ctx.close(); }private final ChannelFutureListener listener = new ChannelFutureListener() { public void operationComplete(ChannelFuture future) throws Exception { // TODO Auto-generated method stub if (future.isSuccess()) { System.out.println("send is success!"); } else { future.cause().printStackTrace(); future.channel().close(); } } }; }

结果如下， 发送数据成功之后，会调用listener的方法，打印send is success：
[root@datanode01-ucloud ~]# hadoop jar client.jar send is success! DiscardOutHandler has been invoker!!

现在我故意发送失败，上面发送的数据格式应该为ByteBuf，然后我们来发送String。
[root@datanode01-ucloud ~]# hadoop jar client.jar send is failed java.lang.UnsupportedOperationException: unsupported message type: String (expected: ByteBuf, FileRegion) at io.netty.channel.nio.AbstractNioByteChannel.filterOutboundMessage(AbstractNioByteChannel.java:281) at io.netty.channel.AbstractChannel$AbstractUnsafe.write(AbstractChannel.java:707) at io.netty.channel.DefaultChannelPipeline$HeadContext.write(DefaultChannelPipeline.java:1122) at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:633) at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:691) at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:681) at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:716) at com.isesol.elasticsearch.DiscardClient.channelActive(DiscardClient.java:18) at io.netty.channel.AbstractChannelHandlerContext.invokeChannelActive(AbstractChannelHandlerContext.java:183) at io.netty.channel.AbstractChannelHandlerContext.fireChannelActive(AbstractChannelHandlerContext.java:169) at io.netty.channel.DefaultChannelPipeline.fireChannelActive(DefaultChannelPipeline.java:817) at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.fulfillConnectPromise(AbstractNioChannel.java:260) at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:290) at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:528) at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468) at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382) at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354) at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:111) at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137) at java.lang.Thread.run(Thread.java:745) DiscardOutHandler has been invoker!!


    推荐阅读


    上一篇：JS之返回字符串最后出现的位置lastIndexOf

    下一篇：加密解密（Base64、AES、MD5、HMACSHA256）