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Netty实践

　　Netty是JBOSS针对网络开发的一套应用框架，它也是在NIO的基础上发展起来的。netty基于异步的事件驱动，具有高性能、高扩展性等特性，它提供了统一的底层协议接口，使得开发者从底层的网络协议（比如 TCP/IP、UDP）中解脱出来。

　　TCP传输面向的是字节流，存在粘包半包问题。Netty提供了三种基本的解码类（显然只有读数据时才会有该问题）来解决粘包拆包问题：LineBasedFrameDecoder、DelimiterBasedFrameDecoder、LengthFieldBasedFrameDecoder。其中，前二者所读码流到达指定长度或遇到分隔符时认为结束，若读到的数据大于指定长度则抛TooLongFrameException并忽略之前读到的码流；最后一者每次读固定长度码流。此外，也针对特定协议提供了一些解决该问题的解码类，如ProtobufVarint32FrameDecoder）

　　Netty封装得很好，使得使用起来比较容易，按照“套路”填代码即可。给几个示例：

1、示例

Maven依赖：

 1         <dependency>
 2             <groupId>io.netty</groupId>
 3             <artifactId>netty-all</artifactId>
 4             <version>5.0.0.Alpha2</version>
 5         </dependency>
 6 
 7         <dependency><!-- 只有使用到Protobuf时才需要 -->
 8             <groupId>com.google.protobuf</groupId>
 9             <artifactId>protobuf-java</artifactId>
10             <version>2.5.0</version>
11         </dependency>

View Code

1.1、服务端/客户端

Server:

 1 public class SimpleChatServer {
 2 
 3     private static int port = 8080;
 4 
 5     public SimpleChatServer(int port) {
 6         this.port = port;
 7     }
 8 
 9     public void run() throws Exception {
10 
11         EventLoopGroup bossGroup = new NioEventLoopGroup();
12         EventLoopGroup workerGroup = new NioEventLoopGroup();
13         try {
14             ServerBootstrap b = new ServerBootstrap();
15             b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 128)
16                     .childHandler(new SimpleChatServerInitializer()).childOption(ChannelOption.SO_KEEPALIVE, true);
17 
18             System.out.println("server 启动了");
19 
20             // 绑定端口，开始接收进来的连接
21             // b.bind(11122);//可以绑定多个端口
22             ChannelFuture f = b.bind(port).sync();
23 
24             // 等待服务器 socket 关闭 。
25             // 在这个例子中，这不会发生，但你可以优雅地关闭你的服务器。
26             f.channel().closeFuture().sync();
27         } finally {
28             workerGroup.shutdownGracefully();
29             bossGroup.shutdownGracefully();
30 
31             System.out.println("server 关闭了");
32         }
33     }
34 
35     public static void main(String[] args) throws Exception {
36         new SimpleChatServer(port).run();
37     }
38 }

SimpleChatServer

 1 public class SimpleChatServerInitializer extends ChannelInitializer<SocketChannel> {
 2     private static final StringDecoder DECODER = new StringDecoder();
 3     private static final StringEncoder ENCODER = new StringEncoder();
 4 
 5     @Override
 6     public void initChannel(SocketChannel ch) throws Exception {// Pipeline里的Handler是从底层开始向上添加的，故流动方向为后添加的输出给先添加的、或先添加的读入给后添加的
 7         ChannelPipeline pipeline = ch.pipeline();
 8 
 9         // 添加ChannelHandler，顺序是敏感的；名字任意，不冲突即可，也可以不指定名字
10 
11         // Netty提供了三种解码器解决粘包拆包问题：LineBasedFrameDecoder、DelimiterBasedFrameDecoder、LengthFieldBasedFrameDecoder。
12         // 其中，前二者所读码流到达指定长度或遇到分隔符时认为结束，若读到的数据大于指定长度则抛TooLongFrameException并忽略之前读到的码流；最后一者每次读固定长度码流。
13         // 也可以继承ByteToMessageDecoder自己处理
14         pipeline.addLast("FrameDecoder", new ProtobufVarint32FrameDecoder());
15         pipeline.addLast("StringDecoder", DECODER);
16 
17         // 解码只会应用于读数据时、编码只会应用于写数据时，因此解码器与编码器添加的先后顺序在客户端和服务端中可不同，但编码器添加的顺序须桶，解码器亦然。
18         pipeline.addLast("StringEncoder", ENCODER);
19 
20         pipeline.addLast("handler", new SimpleChatServerHandler());
21 
22         System.out.println("client " + ch.remoteAddress() + " 连接上");
23     }
24 }

SimpleChatServerInitializer

 1 public class SimpleChatServerHandler extends SimpleChannelInboundHandler<String> {
 2 
 3     public static ChannelGroup channels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
 4 
 5     // 一个客户端连上再断开时，六个事件的触发顺序：加入、(连接上(在SimpleChatServerInitializer中))、在线、异常、掉线、离开
 6     @Override
 7     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {// 在ctx加入本Handler时触发，一般在此做初始化工作，如创建buf
 8         Channel incoming = ctx.channel();
 9         for (Channel channel : channels) {
10             channel.writeAndFlush("[SERVER] - " + incoming.remoteAddress() + " 加入
");
11         }
12         System.out.println("client " + incoming.remoteAddress() + " 加入");
13         channels.add(ctx.channel());
14     }
15 
16     @Override
17     public void channelActive(ChannelHandlerContext ctx) throws Exception {// 当客户端和服务端建立tcp成功之后，Netty的NIO线程会调用channelActive
18         Channel incoming = ctx.channel();
19         System.out.println("client " + incoming.remoteAddress() + " 在线");
20     }
21 
22     @Override
23     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
24         Channel incoming = ctx.channel();
25         System.err.println("client " + incoming.remoteAddress() + " 异常:" + cause.getMessage());
26         // 当出现异常就关闭连接
27         // cause.printStackTrace();
28         ctx.close();
29     }
30 
31     @Override
32     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
33         Channel incoming = ctx.channel();
34         System.out.println("client " + incoming.remoteAddress() + " 掉线");
35     }
36 
37     @Override
38     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {// 从ctx移除本Handler时触发
39         Channel incoming = ctx.channel();
40         for (Channel channel : channels) {
41             channel.writeAndFlush("[SERVER] - " + incoming.remoteAddress() + " 离开
");
42         }
43         System.out.println("client " + incoming.remoteAddress() + " 离开");
44         channels.remove(ctx.channel());
45     }
46 
47     // 优先级高于messageReceived方法，有了这个方法就会屏蔽messageReceived方法
48     // @Override
49     // public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
50     // System.out.println("channelRead");
51     // Channel incoming = ctx.channel();
52     // for (Channel channel : channels) {
53     // if (channel != incoming){
54     // channel.writeAndFlush("[" + incoming.remoteAddress() + "]" + msg + "
");
55     // } else {
56     // channel.writeAndFlush("server: " + msg + "
");
57     // }
58     // }
59     // }
60 
61     @Override
62     protected void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception {
63         Channel incoming = ctx.channel();
64         System.out.println("**" + incoming.remoteAddress() + " send: " + msg);
65         for (Channel channel : channels) {
66             if (channel != incoming) {
67                 // System.out.println("[" + incoming.remoteAddress() + "] " + msg);
68                 channel.writeAndFlush("[" + incoming.remoteAddress() + "] " + msg + "
");
69             } else {
70                 // System.out.println("server: " + msg);
71                 channel.writeAndFlush("server: " + msg + "
");
72             }
73         }
74     }
75 
76 }

SimpleChatServerHandler

Client:

 1 public class SimpleChatClient {
 2 
 3     private String host;
 4     private int port;
 5 
 6     public SimpleChatClient(String host, int port) {
 7         this.host = host;
 8         this.port = port;
 9     }
10 
11     public void run() throws Exception {
12         EventLoopGroup group = new NioEventLoopGroup();
13         try {
14             Bootstrap bootstrap = new Bootstrap().group(group).channel(NioSocketChannel.class)
15                     .handler(new SimpleChatClientInitializer());
16             Channel channel = bootstrap.connect(host, port).sync().channel();
17 
18             Scanner sc = new Scanner(System.in);
19             System.out.println("please enter...");
20             boolean exit = false;
21             // 输入exit，退出系统
22             while (!exit) {
23                 String str = sc.next();
24                 channel.writeAndFlush(str + "
");
25                 if (str.equalsIgnoreCase("exit")) {
26                     exit = true;
27                     channel.close();
28                 }
29             }
30             sc.close();
31         } catch (Exception e) {
32             e.printStackTrace();
33         } finally {
34             group.shutdownGracefully();
35         }
36     }
37 
38     public static void main(String[] args) throws Exception {
39         new SimpleChatClient("localhost", 8080).run();
40     }
41 }

SimpleChatClient

 1 public class SimpleChatClientInitializer extends ChannelInitializer<SocketChannel> {
 2     private static final StringDecoder DECODER = new StringDecoder();
 3     private static final StringEncoder ENCODER = new StringEncoder();
 4 
 5     @Override
 6     public void initChannel(SocketChannel ch) throws Exception {// Pipeline里的Handler是从底层开始向上添加的，故流动方向为后添加的输出给先添加的、或先添加的读入给后添加的
 7         ChannelPipeline pipeline = ch.pipeline();
 8 
 9         // 添加ChannelHandler，顺序是敏感的；名字任意，不冲突即可，也可以不指定名字
10 
11         // Netty提供了三种解码器解决粘包拆包问题：LineBasedFrameDecoder、DelimiterBasedFrameDecoder、LengthFieldBasedFrameDecoder。
12         // 其中，前二者所读码流到达指定长度或遇到分隔符时认为结束，若读到的数据大于指定长度则抛TooLongFrameException并忽略之前读到的码流；最后一者每次读固定长度码流。
13         // 也可以继承ByteToMessageDecoder自己处理
14         pipeline.addLast("FrameDecoder", new ProtobufVarint32FrameDecoder());
15         pipeline.addLast("StringDecoder", DECODER);
16 
17         // 解码只会应用于读数据时、编码只会应用于写数据时，因此解码器与编码器添加的先后顺序在客户端和服务端中可不同，但编码器添加的顺序须桶，解码器亦然。
18         pipeline.addLast("StringEncoder", ENCODER);
19 
20         pipeline.addLast("handler", new SimpleChatClientHandler());
21     }
22 }

SimpleChatClientInitializer

 1 public class SimpleChatClientHandler extends SimpleChannelInboundHandler<String> {
 2 
 3     // 优先级高于messageReceived方法，有了这个方法就会屏蔽messageReceived方法
 4     // @Override
 5     // public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
 6     // System.out.println(msg.toString());
 7     // }
 8 
 9     @Override
10     protected void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception {
11         System.out.println(msg);
12     }
13 }

SimpleChatClientHandler

以下几个是官方示例（翻译）：

1.2、DiscardServer

服务端接收客户端的消息，不返回任何信息：

 1 class DiscardServerHandler extends ChannelHandlerAdapter { // (1)
 2 
 3     // @Override
 4     // public void channelRead(ChannelHandlerContext ctx, Object msg) { // (2)
 5     // // 以静默方式丢弃接收的数据
 6     // ((ByteBuf) msg).release(); // (3)ByteBuf属于引用计数的对象，必须通过release()方法显式释放。
 7     // }
 8 
 9     @Override
10     public void channelRead(ChannelHandlerContext ctx, Object msg) { // (2)
11         ByteBuf in = (ByteBuf) msg;
12         try {
13             System.out.println(in.toString(Charset.defaultCharset()));
14             while (in.isReadable()) { // (1)
15                 System.out.print((char) in.readByte());
16                 System.out.flush();
17             } // 这个低效的循环可以简化为 System.out.println(in.toString(io.netty.util.CharsetUtil.US_ASCII));
18         } finally {
19             ReferenceCountUtil.release(msg);// (2) // 或者写为 in.release();
20         }
21         // 或者直接打印
22         System.out.println("Yes, A new client in = " + ctx.name());
23     }
24 
25     @Override
26     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // (4)
27         // 出现异常时关闭连接。
28         cause.printStackTrace();
29         ctx.close();
30     }
31 }
32 
33 public class DiscardServer {// 可以用telnet连接并输入进行测试，客户端没有任何输出
34     private int port;
35 
36     public DiscardServer(int port
37 
38     ) {
39         this.port = port;
40     }
41 
42     public void run() throws Exception {
43         EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)NioEventLoopGroup是处理I/O操作的多线程事件循环。第一个通常称为“boss”，接受传入连接。 第二个通常称为“worker”，当“boss”接受连接并且向“worker”注册接受连接，则“worker”处理所接受连接的流量。
44                                                             // 使用多少个线程以及如何将它们映射到创建的通道取决于EventLoopGroup实现，甚至可以通过构造函数进行配置。
45         EventLoopGroup workerGroup = new NioEventLoopGroup();
46         try {
47             ServerBootstrap b = new ServerBootstrap(); // (2)
48             b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class) // (3)该类用于实例化新的通道以接受传入连接
49                     .childHandler(new ChannelInitializer<SocketChannel>() { // (4)ChannelInitializer是一个特殊的处理程序，用于帮助用户配置新的通道。 很可能要通过添加一些处理程序。随着应用程序变得复杂，可能会向管道中添加更多处理程序
50                         @Override
51                         public void initChannel(SocketChannel ch) throws Exception {
52                             ch.pipeline().addLast(new DiscardServerHandler());// 每次有新连接都会创建一个新的DiscardServerHandler处理之，，而不是只用一个来处理所有的
53                         }
54                     }).option(ChannelOption.SO_BACKLOG, 128) // (5)指定Channel实现的参数
55                     .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)
56 
57             System.out.println("server 启动了");
58 
59             // Bind and start to accept incoming connections.
60             // b.bind(11122);//可以绑定多个端口
61             ChannelFuture f = b.bind(port).sync(); // (7)
62 
63             // Wait until the server socket is closed.
64             // In this example, this does not happen, but you can do that to gracefully
65             // shut down your server.
66             f.channel().closeFuture().sync();
67         } finally {
68             workerGroup.shutdownGracefully();
69             bossGroup.shutdownGracefully();
70 
71             System.out.println("server 关闭了");
72         }
73     }
74 
75     public static void main(String[] args) throws Exception {
76         int port;
77         if (args.length > 0) {
78             port = Integer.parseInt(args[0]);
79         } else {
80             port = 8080;
81         }
82         new DiscardServer(port).run();// 可以用telnet连接并输入进行测试，客户端没有任何输出
83     }
84 }

DiscardServer

1.3、TimeServer_StremBased

时间服务器：服务端收到客户端连接就往客户端发生时间，发完后就关闭连接；客户端连接上服务端，收到消息后就关闭连接，读的一方需要处理 粘包拆包 的问题

  1 //http://www.yiibai.com/netty/netty-time-server.htmlclass
  2 /**
  3  * 时间服务器<br>
  4  * 服务端收到客户端连接就往客户端发生时间，发完后就关闭连接；客户端连接上服务端，收到消息后就关闭连接。<br>
  5  * 只有读者会有粘包拆包的问题，所以这里只有客户端可能有该问题。
  6  */
  7 class TimeServerHandler_StreamBased extends ChannelHandlerAdapter {
  8     // 因为时间服务器将忽略任何接收到的数据，但是一旦建立连接就发送消息，所以我们不能使用channelRead()方法。而是覆盖channelActive()方法。
  9     @Override
 10     public void channelActive(final ChannelHandlerContext ctx) { // (1)
 11         final ByteBuf time = ctx.alloc().buffer(4); // (2)
 12 
 13         // 在Java NIO中发送消息之前需调用java.nio.ByteBuffer.flip()，但Netty ByteBuf没有这样的方法，它只有两个指针;一个用于读取操作，另一个用于写入操作。当您向ByteBuf写入内容时，写入索引会增加，而读取器索引不会更改。读取器索引和写入器索引分别表示消息的开始和结束位置。
 14         time.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));
 15 
 16         // ChannelHandlerContext.write()(和writeAndFlush())方法返回一个ChannelFuture。
 17         // ChannelFuture表示尚未发生的I/O操作。这意味着，任何请求的操作可能尚未执行，因为所有操作在Netty中是异步的。因此，需要在ChannelFuture完成后调用close()方法。注意，close()也可能不会立即关闭连接，并返回一个ChannelFuture。
 18         final ChannelFuture f = ctx.writeAndFlush(time); // (3)
 19 
 20         // 当写请求完成时，我们如何得到通知？添加监听器
 21         f.addListener(new ChannelFutureListener() {
 22             @Override
 23             public void operationComplete(ChannelFuture future) {
 24                 assert f == future;
 25                 ctx.close();// 发完就关闭连接
 26             }
 27         }); // (4)// 可以使用预定义的监听器来简化代码：f.addListener(ChannelFutureListener.CLOSE);
 28     }
 29 
 30     @Override
 31     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
 32         cause.printStackTrace();
 33         ctx.close();
 34     }
 35 }
 36 
 37 public class TimeServer_StreamBased {
 38     private int port;
 39 
 40     public TimeServer_StreamBased(int port) {
 41         this.port = port;
 42     }
 43 
 44     public void run() throws Exception {
 45         EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)NioEventLoopGroup是处理I/O操作的多线程事件循环。第一个通常称为“boss”，接受传入连接。 第二个通常称为“worker”，当“boss”接受连接并且向“worker”注册接受连接，则“worker”处理所接受连接的流量。
 46                                                             // 使用多少个线程以及如何将它们映射到创建的通道取决于EventLoopGroup实现，甚至可以通过构造函数进行配置。
 47         EventLoopGroup workerGroup = new NioEventLoopGroup();
 48         try {
 49             ServerBootstrap b = new ServerBootstrap(); // (2)
 50             b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class) // (3)该类用于实例化新的通道以接受传入连接
 51                     .childHandler(new ChannelInitializer<SocketChannel>() { // (4)ChannelInitializer是一个特殊的处理程序，用于帮助用户配置新的通道。 很可能要通过添加一些处理程序。随着应用程序变得复杂，可能会向管道中添加更多处理程序
 52                         @Override
 53                         public void initChannel(SocketChannel ch) throws Exception {
 54                             ch.pipeline().addLast(new TimeServerHandler_StreamBased());// 每次有新连接就创建一个新的该handler来处理，而不是只用一个来处理所有的
 55                         }
 56                     }).option(ChannelOption.SO_BACKLOG, 128) // (5)指定Channel实现的参数
 57                     .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)
 58 
 59             System.out.println("server 启动了");
 60 
 61             // Bind and start to accept incoming connections.
 62             // b.bind(11122);//可以绑定多个端口
 63             ChannelFuture f = b.bind(port).sync(); // (7)
 64 
 65             // Wait until the server socket is closed.
 66             // In this example, this does not happen, but you can do that to gracefully
 67             // shut down your server.
 68             f.channel().closeFuture().sync();
 69         } finally {
 70             workerGroup.shutdownGracefully();
 71             bossGroup.shutdownGracefully();
 72 
 73             System.out.println("server 关闭了");
 74         }
 75     }
 76 
 77     public static void main(String[] args) throws Exception {
 78         int port = 8080;
 79 
 80         new TimeServer_StreamBased(port).run();// 可以用telnet连接并输入进行测试，客户端输出二进制的32位整数，所以为乱码
 81     }
 82 }
 83 
 84 class TimeClient_StreamBased {
 85     public static void main(String[] args) throws Exception {
 86         String host = "localhost";
 87         int port = 8080;
 88         EventLoopGroup workerGroup = new NioEventLoopGroup();
 89 
 90         try {
 91             Bootstrap b = new Bootstrap(); // (1)Bootstrap与ServerBootstrap类似，只是它用于非服务器通道，例如客户端或无连接通道。
 92             b.group(workerGroup); // (2)如果只指定一个EventLoopGroup，它将同时用作boss组和worker组。boss组和worker组不是用于客户端。
 93             b.channel(NioSocketChannel.class); // (3)不使用NioServerSocketChannel，而是使用NioSocketChannel来创建客户端通道。
 94             b.option(ChannelOption.SO_KEEPALIVE, true); // (4)这里不像我们使用的ServerBootstrap，所以不使用childOption()，因为客户端SocketChannel没有父类。
 95             b.handler(new ChannelInitializer<SocketChannel>() {
 96                 @Override
 97                 public void initChannel(SocketChannel ch) throws Exception {
 98                     // 以下两种方式都可以解决读取粘包拆包的问题
 99                     ch.pipeline().addLast(new TimeClientHandler_1_TimeDecoder(), new TimeClientHandler_1_withproblem());
100                     // ch.pipeline().addLast(new TimeClientHandler_2());
101                 }
102             });
103 
104             // Start the client.
105             ChannelFuture f = b.connect(host, port).sync(); // (5)应该调用connect()方法，而不是bind()方法
106 
107             // Wait until the connection is closed.
108             f.channel().closeFuture().sync();
109         } finally {
110             workerGroup.shutdownGracefully();
111         }
112     }
113 }
114 
115 /**
116  * 此Handler单独使用的话存在粘包拆包的问题
117  */
118 class TimeClientHandler_1_withproblem extends ChannelHandlerAdapter {
119     @Override
120     public void channelRead(ChannelHandlerContext ctx, Object msg) {// 粘包拆包问题，在TCP/IP的基于流的传输中，接收的数据被存储到套接字接收缓冲器中。不幸的是，基于流的传输的缓冲器不是分组的队列，而是字节的队列。这意味着，即使将两个消息作为两个独立的数据包发送，操作系统也不会将它们视为两个消息，而只是一组字节。
121                                                                     // 因此，不能保证读的是输入的完整。不过，由于返回的是32位int，数据量小，所以这里很少可能发生此问题。
122         ByteBuf m = (ByteBuf) msg; // (1)
123         try {
124             long currentTimeMillis = (m.readUnsignedInt() - 2208988800L) * 1000L;// 每次读取到m的字节数不一定是4，所以存在粘包拆包的问题
125             Date currentTime = new Date(currentTimeMillis);
126             System.out.println("Default Date Format:" + currentTime.toString());
127 
128             SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
129             String dateString = formatter.format(currentTime);
130             // 转换一下成中国人的时间格式
131             System.out.println("Date Format:" + dateString);
132 
133             ctx.close();
134         } finally {
135             m.release();
136         }
137     }
138 
139     @Override
140     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
141         cause.printStackTrace();
142         ctx.close();
143     }
144 }
145 
146 /**
147  * 与TimeClientHandler_1_withproblem搭配使用，解决粘包拆包问题，且易扩展 <br>
148  * <br>
149  * 在客户端的ClientHandler之前加上一层，使得字节够了才往ClientHandler传，以解决粘包拆包的问题
150  */
151 class TimeClientHandler_1_TimeDecoder extends ByteToMessageDecoder { // (1)ByteToMessageDecoder是ChannelHandlerAdapter的一个实现，它使得处理碎片问题变得容易
152     @Override
153     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) { // (2)
154         if (in.readableBytes() < 4) {
155             return; // (3)
156         }
157         out.add(in.readBytes(4)); // (4)
158     }
159 }
160 
161 /**
162  * 此的Handler能解决读取粘包拆包问题，但可扩展性差<br>
163  * <br>
164  * 在客户端的ClientHandler里解决粘包拆包问题：字节够了才读
165  */
166 class TimeClientHandler_2 extends ChannelHandlerAdapter {
167     private ByteBuf buf;
168 
169     @Override
170     public void handlerAdded(ChannelHandlerContext ctx) {
171         buf = ctx.alloc().buffer(4); // (1)初始化
172     }
173 
174     @Override
175     public void handlerRemoved(ChannelHandlerContext ctx) {
176         buf.release(); // (1)初始化的释放
177         buf = null;
178     }
179 
180     @Override
181     public void channelRead(ChannelHandlerContext ctx, Object msg) {
182         ByteBuf m = (ByteBuf) msg;
183         buf.writeBytes(m); // (2)
184         m.release();
185 
186         if (buf.readableBytes() >= 4) { // (3)
187             long currentTimeMillis = (buf.readUnsignedInt() - 2208988800L) * 1000L;
188             System.out.println(new Date(currentTimeMillis));
189             ctx.close();
190         }
191     }
192 
193     @Override
194     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
195         cause.printStackTrace();
196         ctx.close();
197     }
198 }

TimeServer_StreamBased

1.4、TimeServer_POJOBased

时间服务器：同上，但通过POJO来通信，同样，读的一方需要处理 粘包拆包 的问题

  1 /**
  2  * 时间服务器<br>
  3  * 服务端收到客户端连接就往客户端发送时间，发完后就关闭连接；客户端连接上服务端，收到消息后就关闭连接。<br>
  4  * 由于只有服务端往客户端发数据，所以服务端只要encode、客户端只要decode
  5  */
  6 
  7 class UnixTime {
  8     private final long value;
  9 
 10     public UnixTime() {
 11         this(System.currentTimeMillis() / 1000L + 2208988800L);
 12     }
 13 
 14     public UnixTime(long value) {
 15         this.value = value;
 16     }
 17 
 18     public long value() {
 19         return value;
 20     }
 21 
 22     @Override
 23     public String toString() {
 24         Date date = new Date((value() - 2208988800L) * 1000L);
 25         SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 26         String dateString = formatter.format(date);
 27         return dateString;
 28     }
 29 }
 30 
 31 class TimeEncoder_POJOBased extends MessageToByteEncoder<UnixTime> {
 32     @Override
 33     protected void encode(ChannelHandlerContext ctx, UnixTime msg, ByteBuf out) {
 34         out.writeInt((int) msg.value());
 35     }
 36 }
 37 
 38 class TimeServerHandler_POJOBased extends ChannelHandlerAdapter {
 39     @Override
 40     public void channelActive(ChannelHandlerContext ctx) {// 当客户端和服务端建立tcp成功之后，Netty的NIO线程会调用channelActive
 41         ChannelFuture f = ctx.writeAndFlush(new UnixTime());
 42         f.addListener(ChannelFutureListener.CLOSE);
 43     }
 44 
 45     @Override
 46     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {// 在ctx加入本Handler时触发，一般在此做初始化工作，如创建buf
 47         Channel incoming = ctx.channel();
 48         System.out.println("client " + incoming.remoteAddress() + " 加入");
 49     }
 50 
 51     @Override
 52     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {// 从ctx移除本Handler时触发
 53         Channel incoming = ctx.channel();
 54         System.out.println("client " + incoming.remoteAddress() + " 离开");
 55     }
 56 
 57     @Override
 58     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
 59         cause.printStackTrace();
 60         ctx.close();
 61     }
 62 }
 63 
 64 public class TimeServer_POJOBased {
 65     private int port;
 66 
 67     public TimeServer_POJOBased(int port) {
 68         this.port = port;
 69     }
 70 
 71     public void run() throws Exception {
 72         // NioEventLoopGroup类是个线程组，包含一组NIO线程，用于网络事件的处理（实际上它就是Reactor线程组）。 创建的2个线程组，1个用于服务端接收客户端的连接，另一个用于SocketChannel的 网络读写
 73         EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)
 74         EventLoopGroup workerGroup = new NioEventLoopGroup();
 75         try {
 76             // ServerBootstrap类是启动NIO服务器的辅助启动类
 77             ServerBootstrap b = new ServerBootstrap(); // (2)
 78             b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class) // (3)
 79                     .option(ChannelOption.SO_BACKLOG, 128).childHandler(new ChannelInitializer<SocketChannel>() { // (4)
 80                         @Override
 81                         public void initChannel(SocketChannel ch) throws Exception {
 82                             // Pipeline里的Handler是从底层开始向上叠加的，即后者输出给前者、或前者读出的给后者
 83                             // 由于只有服务端往客户端发数据，所以服务端只要encode、客户端只要decode
 84                             ch.pipeline().addLast(new TimeEncoder_POJOBased(), new TimeServerHandler_POJOBased());
 85                         }
 86                     })// (5)
 87                     .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)
 88 
 89             System.out.println("server 启动了");
 90 
 91             // 绑定端口，开始接收进来的连接
 92             // b.bind(11122);//可以绑定多个端口
 93             ChannelFuture f = b.bind(port).sync(); // (7)
 94 
 95             // 等待服务器 socket 关闭 。
 96             // 在这个例子中，这不会发生，但你可以优雅地关闭你的服务器。
 97             f.channel().closeFuture().sync();
 98         } finally {
 99             workerGroup.shutdownGracefully();
100             bossGroup.shutdownGracefully();
101             System.out.println("server 关闭了");
102         }
103     }
104 
105     public static void main(String[] args) throws Exception {
106         int port;
107         if (args.length > 0) {
108             port = Integer.parseInt(args[0]);
109         } else {
110             port = 8080;
111         }
112         new TimeServer_POJOBased(port).run();
113     }
114 }
115 
116 class TimeClient_POJOBased {
117 
118     public static void main(String[] args) throws Exception {
119 
120         String host = "127.0.0.1";
121         int port = 8080;
122         EventLoopGroup workerGroup = new NioEventLoopGroup();
123 
124         try {
125             Bootstrap b = new Bootstrap(); // (1)
126             b.group(workerGroup); // (2)
127             b.channel(NioSocketChannel.class); // (3)
128             b.option(ChannelOption.SO_KEEPALIVE, true); // (4)
129             b.handler(new ChannelInitializer<SocketChannel>() {
130                 @Override
131                 public void initChannel(SocketChannel ch) throws Exception {
132                     // Pipeline里的Handler是从底层开始向上添加的，故流动方向为后添加的输出给先添加的、或先添加的读入给后添加的
133                     // 由于只有服务端往客户端发数据，所以服务端只要encode、客户端只要decode
134                     ch.pipeline().addLast(new TimeDecoder_POJOBased(), new TimeClientHandler_POJOBased());
135                 }
136             });
137 
138             // 启动客户端
139             ChannelFuture f = b.connect(host, port).sync(); // (5)
140 
141             // 等待连接关闭
142             f.channel().closeFuture().sync();
143         } finally {
144             workerGroup.shutdownGracefully();
145         }
146     }
147 }
148 
149 class TimeDecoder_POJOBased extends ByteToMessageDecoder {
150     @Override
151     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
152         // TODO Auto-generated method stub
153         if (in.readableBytes() < 4) {// 只有读者存在粘包半包问题，这里不少于4个字节时才处理，以避免该问题
154             return;
155         }
156         out.add(new UnixTime(in.readUnsignedInt()));
157     }
158 }
159 
160 class TimeClientHandler_POJOBased extends ChannelHandlerAdapter {
161     // @Override
162     public void channelRead(ChannelHandlerContext ctx, Object msg) {
163         UnixTime m = (UnixTime) msg;
164         System.out.println(m);
165         ctx.close();
166     }
167 
168     @Override
169     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
170         cause.printStackTrace();
171         ctx.close();
172     }
173 }

TimeServer_POJOBased

1.5、结合Protobuf

　　（就是把自动生成的类当成一个JavaBean来用，但是该JavaBean比普通的Bean更强大，如包含了与Protobuf格式间进行序列化/反序列化的方法）

Netty提供了与Protobuf相关的解决粘包半包问题的编解码器(ByteBuf与ByteBuf间) 以及 ByteBuf与自定义Protobuf类间的编解码器：

ProtobufVarint32FrameDecoder()
ProtobufVarint32LengthFieldPrepender()
ProtobufDecoder(Custom Protobuf Class)
ProtobufEncoder()

示例（需要添加Protobuf依赖，）：

  1 public final class PersonProbuf {
  2     private PersonProbuf() {
  3     }
  4 
  5     public static void registerAllExtensions(com.google.protobuf.ExtensionRegistry registry) {
  6     }
  7 
  8     public interface PersonOrBuilder extends com.google.protobuf.MessageOrBuilder {
  9 
 10         // optional int64 id = 1;
 11         /**
 12          * <code>optional int64 id = 1;</code>
 13          *
 14          * <pre>
 15          *可选的字段，为64位整数..
 16          * </pre>
 17          */
 18         boolean hasId();
 19 
 20         /**
 21          * <code>optional int64 id = 1;</code>
 22          *
 23          * <pre>
 24          *可选的字段，为64位整数..
 25          * </pre>
 26          */
 27         long getId();
 28 
 29         // optional string name = 2;
 30         /**
 31          * <code>optional string name = 2;</code>
 32          */
 33         boolean hasName();
 34 
 35         /**
 36          * <code>optional string name = 2;</code>
 37          */
 38         java.lang.String getName();
 39 
 40         /**
 41          * <code>optional string name = 2;</code>
 42          */
 43         com.google.protobuf.ByteString getNameBytes();
 44 
 45         // optional string sex = 3;
 46         /**
 47          * <code>optional string sex = 3;</code>
 48          */
 49         boolean hasSex();
 50 
 51         /**
 52          * <code>optional string sex = 3;</code>
 53          */
 54         java.lang.String getSex();
 55 
 56         /**
 57          * <code>optional string sex = 3;</code>
 58          */
 59         com.google.protobuf.ByteString getSexBytes();
 60 
 61         // optional string tel = 4;
 62         /**
 63          * <code>optional string tel = 4;</code>
 64          */
 65         boolean hasTel();
 66 
 67         /**
 68          * <code>optional string tel = 4;</code>
 69          */
 70         java.lang.String getTel();
 71 
 72         /**
 73          * <code>optional string tel = 4;</code>
 74          */
 75         com.google.protobuf.ByteString getTelBytes();
 76     }
 77 
 78     /**
 79      * Protobuf type {@code Person}
 80      */
 81     public static final class Person extends com.google.protobuf.GeneratedMessage implements PersonOrBuilder {
 82         // Use Person.newBuilder() to construct.
 83         private Person(com.google.protobuf.GeneratedMessage.Builder<?> builder) {
 84             super(builder);
 85             this.unknownFields = builder.getUnknownFields();
 86         }
 87 
 88         private Person(boolean noInit) {
 89             this.unknownFields = com.google.protobuf.UnknownFieldSet.getDefaultInstance();
 90         }
 91 
 92         private static final Person defaultInstance;
 93 
 94         public static Person getDefaultInstance() {
 95             return defaultInstance;
 96         }
 97 
 98         public Person getDefaultInstanceForType() {
 99             return defaultInstance;
100         }
101 
102         private final com.google.protobuf.UnknownFieldSet unknownFields;
103 
104         @java.lang.Override
105         public final com.google.protobuf.UnknownFieldSet getUnknownFields() {
106             return this.unknownFields;
107         }
108 
109         private Person(com.google.protobuf.CodedInputStream input,
110                 com.google.protobuf.ExtensionRegistryLite extensionRegistry)
111                 throws com.google.protobuf.InvalidProtocolBufferException {
112             initFields();
113             int mutable_bitField0_ = 0;
114             com.google.protobuf.UnknownFieldSet.Builder unknownFields = com.google.protobuf.UnknownFieldSet
115                     .newBuilder();
116             try {
117                 boolean done = false;
118                 while (!done) {
119                     int tag = input.readTag();
120                     switch (tag) {
121                     case 0:
122                         done = true;
123                         break;
124                     default: {
125                         if (!parseUnknownField(input, unknownFields, extensionRegistry, tag)) {
126                             done = true;
127                         }
128                         break;
129                     }
130                     case 8: {
131                         bitField0_ |= 0x00000001;
132                         id_ = input.readInt64();
133                         break;
134                     }
135                     case 18: {
136                         bitField0_ |= 0x00000002;
137                         name_ = input.readBytes();
138                         break;
139                     }
140                     case 26: {
141                         bitField0_ |= 0x00000004;
142                         sex_ = input.readBytes();
143                         break;
144                     }
145                     case 34: {
146                         bitField0_ |= 0x00000008;
147                         tel_ = input.readBytes();
148                         break;
149                     }
150                     }
151                 }
152             } catch (com.google.protobuf.InvalidProtocolBufferException e) {
153                 throw e.setUnfinishedMessage(this);
154             } catch (java.io.IOException e) {
155                 throw new com.google.protobuf.InvalidProtocolBufferException(e.getMessage()).setUnfinishedMessage(this);
156             } finally {
157                 this.unknownFields = unknownFields.build();
158                 makeExtensionsImmutable();
159             }
160         }
161 
162         public static final com.google.protobuf.Descriptors.Descriptor getDescriptor() {
163             return PersonProbuf.internal_static_Person_descriptor;
164         }
165 
166         protected com.google.protobuf.GeneratedMessage.FieldAccessorTable internalGetFieldAccessorTable() {
167             return PersonProbuf.internal_static_Person_fieldAccessorTable
168                     .ensureFieldAccessorsInitialized(PersonProbuf.Person.class, PersonProbuf.Person.Builder.class);
169         }
170 
171         public static com.google.protobuf.Parser<Person> PARSER = new com.google.protobuf.AbstractParser<Person>() {
172             public Person parsePartialFrom(com.google.protobuf.CodedInputStream input,
173                     com.google.protobuf.ExtensionRegistryLite extensionRegistry)
174                     throws com.google.protobuf.InvalidProtocolBufferException {
175                 return new Person(input, extensionRegistry);
176             }
177         };
178 
179         @java.lang.Override
180         public com.google.protobuf.Parser<Person> getParserForType() {
181             return PARSER;
182         }
183 
184         private int bitField0_;
185         // optional int64 id = 1;
186         public static final int ID_FIELD_NUMBER = 1;
187         private long id_;
188 
189         /**
190          * <code>optional int64 id = 1;</code>
191          *
192          * <pre>
193          *可选的字段，为64位整数..
194          * </pre>
195          */
196         public boolean hasId() {
197             return ((bitField0_ & 0x00000001) == 0x00000001);
198         }
199 
200         /**
201          * <code>optional int64 id = 1;</code>
202          *
203          * <pre>
204          *可选的字段，为64位整数..
205          * </pre>
206          */
207         public long getId() {
208             return id_;
209         }
210 
211         // optional string name = 2;
212         public static final int NAME_FIELD_NUMBER = 2;
213         private java.lang.Object name_;
214 
215         /**
216          * <code>optional string name = 2;</code>
217          */
218         public boolean hasName() {
219             return ((bitField0_ & 0x00000002) == 0x00000002);
220         }
221 
222         /**
223          * <code>optional string name = 2;</code>
224          */
225         public java.lang.String getName() {
226             java.lang.Object ref = name_;
227             if (ref instanceof java.lang.String) {
228                 return (java.lang.String) ref;
229             } else {
230                 com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
231                 java.lang.String s = bs.toStringUtf8();
232                 if (bs.isValidUtf8()) {
233                     name_ = s;
234                 }
235                 return s;
236             }
237         }
238 
239         /**
240          * <code>optional string name = 2;</code>
241          */
242         public com.google.protobuf.ByteString getNameBytes() {
243             java.lang.Object ref = name_;
244             if (ref instanceof java.lang.String) {
245                 com.google.protobuf.ByteString b = com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
246                 name_ = b;
247                 return b;
248             } else {
249                 return (com.google.protobuf.ByteString) ref;
250             }
251         }
252 
253         // optional string sex = 3;
254         public static final int SEX_FIELD_NUMBER = 3;
255         private java.lang.Object sex_;
256 
257         /**
258          * <code>optional string sex = 3;</code>
259          */
260         public boolean hasSex() {
261             return ((bitField0_ & 0x00000004) == 0x00000004);
262         }
263 
264         /**
265          * <code>optional string sex = 3;</code>
266          */
267         public java.lang.String getSex() {
268             java.lang.Object ref = sex_;
269             if (ref instanceof java.lang.String) {
270                 return (java.lang.String) ref;
271             } else {
272                 com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
273                 java.lang.String s = bs.toStringUtf8();
274                 if (bs.isValidUtf8()) {
275                     sex_ = s;
276                 }
277                 return s;
278             }
279         }
280 
281         /**
282          * <code>optional string sex = 3;</code>
283          */
284         public com.google.protobuf.ByteString getSexBytes() {
285             java.lang.Object ref = sex_;
286             if (ref instanceof java.lang.String) {
287                 com.google.protobuf.ByteString b = com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
288                 sex_ = b;
289                 return b;
290             } else {
291                 return (com.google.protobuf.ByteString) ref;
292             }
293         }
294 
295         // optional string tel = 4;
296         public static final int TEL_FIELD_NUMBER = 4;
297         private java.lang.Object tel_;
298 
299         /**
300          * <code>optional string tel = 4;</code>
301          */
302         public boolean hasTel() {
303             return ((bitField0_ & 0x00000008) == 0x00000008);
304         }
305 
306         /**
307          * <code>optional string tel = 4;</code>
308          */
309         public java.lang.String getTel() {
310             java.lang.Object ref = tel_;
311             if (ref instanceof java.lang.String) {
312                 return (java.lang.String) ref;
313             } else {
314                 com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
315                 java.lang.String s = bs.toStringUtf8();
316                 if (bs.isValidUtf8()) {
317                     tel_ = s;
318                 }
319                 return s;
320             }
321         }
322 
323         /**
324          * <code>optional string tel = 4;</code>
325          */
326         public com.google.protobuf.ByteString getTelBytes() {
327             java.lang.Object ref = tel_;
328             if (ref instanceof java.lang.String) {
329                 com.google.protobuf.ByteString b = com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
330                 tel_ = b;
331                 return b;
332             } else {
333                 return (com.google.protobuf.ByteString) ref;
334             }
335         }
336 
337         private void initFields() {
338             id_ = 0L;
339             name_ = "";
340             sex_ = "";
341             tel_ = "";
342         }
343 
344         private byte memoizedIsInitialized = -1;
345 
346         public final boolean isInitialized() {
347             byte isInitialized = memoizedIsInitialized;
348             if (isInitialized != -1)
349                 return isInitialized == 1;
350 
351             memoizedIsInitialized = 1;
352             return true;
353         }
354 
355         public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
356             getSerializedSize();
357             if (((bitField0_ & 0x00000001) == 0x00000001)) {
358                 output.writeInt64(1, id_);
359             }
360             if (((bitField0_ & 0x00000002) == 0x00000002)) {
361                 output.writeBytes(2, getNameBytes());
362             }
363             if (((bitField0_ & 0x00000004) == 0x00000004)) {
364                 output.writeBytes(3, getSexBytes());
365             }
366             if (((bitField0_ & 0x00000008) == 0x00000008)) {
367                 output.writeBytes(4, getTelBytes());
368             }
369             getUnknownFields().writeTo(output);
370         }
371 
372         private int memoizedSerializedSize = -1;
373 
374         public int getSerializedSize() {
375             int size = memoizedSerializedSize;
376             if (size != -1)
377                 return size;
378 
379             size = 0;
380             if (((bitField0_ & 0x00000001) == 0x00000001)) {
381                 size += com.google.protobuf.CodedOutputStream.computeInt64Size(1, id_);
382             }
383             if (((bitField0_ & 0x00000002) == 0x00000002)) {
384                 size += com.google.protobuf.CodedOutputStream.computeBytesSize(2, getNameBytes());
385             }
386             if (((bitField0_ & 0x00000004) == 0x00000004)) {
387                 size += com.google.protobuf.CodedOutputStream.computeBytesSize(3, getSexBytes());
388             }
389             if (((bitField0_ & 0x00000008) == 0x00000008)) {
390                 size += com.google.protobuf.CodedOutputStream.computeBytesSize(4, getTelBytes());
391             }
392             size += getUnknownFields().getSerializedSize();
393             memoizedSerializedSize = size;
394             return size;
395         }
396 
397         private static final long serialVersionUID = 0L;
398 
399         @java.lang.Override
400         protected java.lang.Object writeReplace() throws java.io.ObjectStreamException {
401             return super.writeReplace();
402         }
403 
404         public static PersonProbuf.Person parseFrom(com.google.protobuf.ByteString data)
405                 throws com.google.protobuf.InvalidProtocolBufferException {
406             return PARSER.parseFrom(data);
407         }
408 
409         public static PersonProbuf.Person parseFrom(com.google.protobuf.ByteString data,
410                 com.google.protobuf.ExtensionRegistryLite extensionRegistry)
411                 throws com.google.protobuf.InvalidProtocolBufferException {
412             return PARSER.parseFrom(data, extensionRegistry);
413         }
414 
415         public static PersonProbuf.Person parseFrom(byte[] data)
416                 throws com.google.protobuf.InvalidProtocolBufferException {
417             return PARSER.parseFrom(data);
418         }
419 
420         public static PersonProbuf.Person parseFrom(byte[] data,
421                 com.google.protobuf.ExtensionRegistryLite extensionRegistry)
422                 throws com.google.protobuf.InvalidProtocolBufferException {
423             return PARSER.parseFrom(data, extensionRegistry);
424         }
425 
426         public static PersonProbuf.Person parseFrom(java.io.InputStream input) throws java.io.IOException {
427             return PARSER.parseFrom(input);
428         }
429 
430         public static PersonProbuf.Person parseFrom(java.io.InputStream input,
431                 com.google.protobuf.ExtensionRegistryLite extensionRegistry) throws java.io.IOException {
432             return PARSER.parseFrom(input, extensionRegistry);
433         }
434 
435         public static PersonProbuf.Person parseDelimitedFrom(java.io.InputStream input) throws java.io.IOException {
436             return PARSER.parseDelimitedFrom(input);
437         }
438 
439         public static PersonProbuf.Person parseDelimitedFrom(java.io.InputStream input,
440                 com.google.protobuf.ExtensionRegistryLite extensionRegistry) throws java.io.IOException {
441             return PARSER.parseDelimitedFrom(input, extensionRegistry);
442         }
443 
444         public static PersonProbuf.Person parseFrom(com.google.protobuf.CodedInputStream input)
445                 throws java.io.IOException {
446             return PARSER.parseFrom(input);
447         }
448 
449         public static PersonProbuf.Person parseFrom(com.google.protobuf.CodedInputStream input,
450                 com.google.protobuf.ExtensionRegistryLite extensionRegistry) throws java.io.IOException {
451             return PARSER.parseFrom(input, extensionRegistry);
452         }
453 
454         public static Builder newBuilder() {
455             return Builder.create();
456         }
457 
458         public Builder newBuilderForType() {
459             return newBuilder();
460         }
461 
462         public static Builder newBuilder(PersonProbuf.Person prototype) {
463             return newBuilder().mergeFrom(prototype);
464         }
465 
466         public Builder toBuilder() {
467             return newBuilder(this);
468         }
469 
470         @java.lang.Override
471         protected Builder newBuilderForType(com.google.protobuf.GeneratedMessage.BuilderParent parent) {
472             Builder builder = new Builder(parent);
473             return builder;
474         }
475 
476         /**
477          * Protobuf type {@code Person}
478          */
479         public static final class Builder extends com.google.protobuf.GeneratedMessage.Builder<Builder>
480                 implements PersonProbuf.PersonOrBuilder {
481             public static final com.google.protobuf.Descriptors.Descriptor getDescriptor() {
482                 return PersonProbuf.internal_static_Person_descriptor;
483             }
484 
485             protected com.google.protobuf.GeneratedMessage.FieldAccessorTable internalGetFieldAccessorTable() {
486                 return PersonProbuf.internal_static_Person_fieldAccessorTable
487                         .ensureFieldAccessorsInitialized(PersonProbuf.Person.class, PersonProbuf.Person.Builder.class);
488             }
489 
490             // Construct using PersonProbuf.Person.newBuilder()
491             private Builder() {
492                 maybeForceBuilderInitialization();
493             }
494 
495             private Builder(com.google.protobuf.GeneratedMessage.BuilderParent parent) {
496                 super(parent);
497                 maybeForceBuilderInitialization();
498             }
499 
500             private void maybeForceBuilderInitialization() {
501                 if (com.google.protobuf.GeneratedMessage.alwaysUseFieldBuilders) {
502                 }
503             }
504 
505             private static Builder create() {
506                 return new Builder();
507             }
508 
509             public Builder clear() {
510                 super.clear();
511                 id_ = 0L;
512                 bitField0_ = (bitField0_ & ~0x00000001);
513                 name_ = "";
514                 bitField0_ = (bitField0_ & ~0x00000002);
515                 sex_ = "";
516                 bitField0_ = (bitField0_ & ~0x00000004);
517                 tel_ = "";
518                 bitField0_ = (bitField0_ & ~0x00000008);
519                 return this;
520             }
521 
522             public Builder clone() {
523                 return create().mergeFrom(buildPartial());
524             }
525 
526             public com.google.protobuf.Descriptors.Descriptor getDescriptorForType() {
527                 return PersonProbuf.internal_static_Person_descriptor;
528             }
529 
530             public PersonProbuf.Person getDefaultInstanceForType() {
531                 return PersonProbuf.Person.getDefaultInstance();
532             }
533 
534             public PersonProbuf.Person build() {
535                 PersonProbuf.Person result = buildPartial();
536                 if (!result.isInitialized()) {
537                     throw newUninitializedMessageException(result);
538                 }
539                 return result;
540             }
541 
542             public PersonProbuf.Person buildPartial() {
543                 PersonProbuf.Person result = new PersonProbuf.Person(this);
544                 int from_bitField0_ = bitField0_;
545                 int to_bitField0_ = 0;
546                 if (((from_bitField0_ & 0x00000001) == 0x00000001)) {
547                     to_bitField0_ |= 0x00000001;
548                 }
549                 result.id_ = id_;
550                 if (((from_bitField0_ & 0x00000002) == 0x00000002)) {
551                     to_bitField0_ |= 0x00000002;
552                 }
553                 result.name_ = name_;
554                 if (((from_bitField0_ & 0x00000004) == 0x00000004)) {
555                     to_bitField0_ |= 0x00000004;
556                 }
557                 result.sex_ = sex_;
558                 if (((from_bitField0_ & 0x00000008) == 0x00000008)) {
559                     to_bitField0_ |= 0x00000008;
560                 }
561                 result.tel_ = tel_;
562                 result.bitField0_ = to_bitField0_;
563                 onBuilt();
564                 return result;
565             }
566 
567             public Builder mergeFrom(com.google.protobuf.Message other) {
568                 if (other instanceof PersonProbuf.Person) {
569                     return mergeFrom((PersonProbuf.Person) other);
570                 } else {
571                     super.mergeFrom(other);
572                     return this;
573                 }
574             }
575 
576             public Builder mergeFrom(PersonProbuf.Person other) {
577                 if (other == PersonProbuf.Person.getDefaultInstance())
578                     return this;
579                 if (other.hasId()) {
580                     setId(other.getId());
581                 }
582                 if (other.hasName()) {
583                     bitField0_ |= 0x00000002;
584                     name_ = other.name_;
585                     onChanged();
586                 }
587                 if (other.hasSex()) {
588                     bitField0_ |= 0x00000004;
589                     sex_ = other.sex_;
590                     onChanged();
591                 }
592                 if (other.hasTel()) {
593                     bitField0_ |= 0x00000008;
594                     tel_ = other.tel_;
595                     onChanged();
596                 }
597                 this.mergeUnknownFields(other.getUnknownFields());
598                 return this;
599             }
600 
601             public final boolean isInitialized() {
602                 return true;
603             }
604 
605             public Builder mergeFrom(com.google.protobuf.CodedInputStream input,
606                     com.google.protobuf.ExtensionRegistryLite extensionRegistry) throws java.io.IOException {
607                 PersonProbuf.Person parsedMessage = null;
608                 try {
609                     parsedMessage = PARSER.parsePartialFrom(input, extensionRegistry);
610                 } catch (com.google.protobuf.InvalidProtocolBufferException e) {
611                     parsedMessage = (PersonProbuf.Person) e.getUnfinishedMessage();
612                     throw e;
613                 } finally {
614                     if (parsedMessage != null) {
615                         mergeFrom(parsedMessage);
616                     }
617                 }
618                 return this;
619             }
620 
621             private int bitField0_;
622 
623             // optional int64 id = 1;
624             private long id_;
625 
626             /**
627              * <code>optional int64 id = 1;</code>
628              *
629              * <pre>
630              *可选的字段，为64位整数..
631              * </pre>
632              */
633             public boolean hasId() {
634                 return ((bitField0_ & 0x00000001) == 0x00000001);
635             }
636 
637             /**
638              * <code>optional int64 id = 1;</code>
639              *
640              * <pre>
641              *可选的字段，为64位整数..
642              * </pre>
643              */
644             public long getId() {
645                 return id_;
646             }
647 
648             /**
649              * <code>optional int64 id = 1;</code>
650              *
651              * <pre>
652              *可选的字段，为64位整数..
653              * </pre>
654              */
655             public Builder setId(long value) {
656                 bitField0_ |= 0x00000001;
657                 id_ = value;
658                 onChanged();
659                 return this;
660             }
661 
662             /**
663              * <code>optional int64 id = 1;</code>
664              *
665              * <pre>
666              *可选的字段，为64位整数..
667              * </pre>
668              */
669             public Builder clearId() {
670                 bitField0_ = (bitField0_ & ~0x00000001);
671                 id_ = 0L;
672                 onChanged();
673                 return this;
674             }
675 
676             // optional string name = 2;
677             private java.lang.Object name_ = "";
678 
679             /**
680              * <code>optional string name = 2;</code>
681              */
682             public boolean hasName() {
683                 return ((bitField0_ & 0x00000002) == 0x00000002);
684             }
685 
686             /**
687              * <code>optional string name = 2;</code>
688              */
689             public java.lang.String getName() {
690                 java.lang.Object ref = name_;
691                 if (!(ref instanceof java.lang.String)) {
692                     java.lang.String s = ((com.google.protobuf.ByteString) ref).toStringUtf8();
693                     name_ = s;
694                     return s;
695                 } else {
696                     return (java.lang.String) ref;
697                 }
698             }
699 
700             /**
701              * <code>optional string name = 2;</code>
702              */
703             public com.google.protobuf.ByteString getNameBytes() {
704                 java.lang.Object ref = name_;
705                 if (ref instanceof String) {
706                     com.google.protobuf.ByteString b = com.google.protobuf.ByteString
707                             .copyFromUtf8((java.lang.String) ref);
708                     name_ = b;
709                     return b;
710                 } else {
711                     return (com.google.protobuf.ByteString) ref;
712                 }
713             }
714 
715             /**
716              * <code>optional string name = 2;</code>
717              */
718             public Builder setName(java.lang.String value) {
719                 if (value == null) {
720                     throw new NullPointerException();
721                 }
722                 bitField0_ |= 0x00000002;
723                 name_ = value;
724                 onChanged();
725                 return this;
726             }
727 
728             /**
729              * <code>optional string name = 2;</code>
730              */
731             public Builder clearName() {
732                 bitField0_ = (bitField0_ & ~0x00000002);
733                 name_ = getDefaultInstance().getName();
734                 onChanged();
735                 return this;
736             }
737 
738             /**
739              * <code>optional string name = 2;</code>
740              */
741             public Builder setNameBytes(com.google.protobuf.ByteString value) {
742                 if (value == null) {
743                     throw new NullPointerException();
744                 }
745                 bitField0_ |= 0x00000002;
746                 name_ = value;
747                 onChanged();
748                 return this;
749             }
750 
751             // optional string sex = 3;
752             private java.lang.Object sex_ = "";
753 
754             /**
755              * <code>optional string sex = 3;</code>
756              */
757             public boolean hasSex() {
758                 return ((bitField0_ & 0x00000004) == 0x00000004);
759             }
760 
761             /**
762              * <code>optional string sex = 3;</code>
763              */
764             public java.lang.String getSex() {
765                 java.lang.Object ref = sex_;
766                 if (!(ref instanceof java.lang.String)) {
767                     java.lang.String s = ((com.google.protobuf.ByteString) ref).toStringUtf8();
768                     sex_ = s;
769                     return s;
770                 } else {
771                     return (java.lang.String) ref;
772                 }
773             }
774 
775             /**
776              * <code>optional string sex = 3;</code>
777              */
778             public com.google.protobuf.ByteString getSexBytes() {
779                 java.lang.Object ref = sex_;
780                 if (ref instanceof String) {
781                     com.google.protobuf.ByteString b = com.google.protobuf.ByteString
782                             .copyFromUtf8((java.lang.String) ref);
783                     sex_ = b;
784                     return b;
785                 } else {
786                     return (com.google.protobuf.ByteString) ref;
787                 }
788             }
789 
790             /**
791              * <code>optional string sex = 3;</code>
792              */
793             public Builder setSex(java.lang.String value) {
794                 if (value == null) {
795                     throw new NullPointerException();
796                 }
797                 bitField0_ |= 0x00000004;
798                 sex_ = value;
799                 onChanged();
800                 return this;
801             }
802 
803             /**
804              * <code>optional string sex = 3;</code>
805              */
806             public Builder clearSex() {
807                 bitField0_ = (bitField0_ & ~0x00000004);
808                 sex_ = getDefaultInstance().getSex();
809                 onChanged();
810                 return this;
811             }
812 
813             /**
814              * <code>optional string sex = 3;</code>
815              */
816             public Builder setSexBytes(com.google.protobuf.ByteString value) {
817                 if (value == null) {
818                     throw new NullPointerException();
819                 }
820                 bitField0_ |= 0x00000004;
821                 sex_ = value;
822                 onChanged();
823                 return this;
824             }
825 
826             // optional string tel = 4;
827             private java.lang.Object tel_ = "";
828 
829             /**
830              * <code>optional string tel = 4;</code>
831              */
832             public boolean hasTel() {
833                 return ((bitField0_ & 0x00000008) == 0x00000008);
834             }
835 
836             /**
837              * <code>optional string tel = 4;</code>
838              */
839             public java.lang.String getTel() {
840                 java.lang.Object ref = tel_;
841                 if (!(ref instanceof java.lang.String)) {
842                     java.lang.String s = ((com.google.protobuf.ByteString) ref).toStringUtf8();
843                     tel_ = s;
844                     return s;
845                 } else {
846                     return (java.lang.String) ref;
847                 }
848             }
849 
850             /**
851              * <code>optional string tel = 4;</code>
852              */
853             public com.google.protobuf.ByteString getTelBytes() {
854                 java.lang.Object ref = tel_;
855                 if (ref instanceof String) {
856                     com.google.protobuf.ByteString b = com.google.protobuf.ByteString
857                             .copyFromUtf8((java.lang.String) ref);
858                     tel_ = b;
859                     return b;
860                 } else {
861                     return (com.google.protobuf.ByteString) ref;
862                 }
863             }
864 
865             /**
866              * <code>optional string tel = 4;</code>
867              */
868             public Builder setTel(java.lang.String value) {
869                 if (value == null) {
870                     throw new NullPointerException();
871                 }
872                 bitField0_ |= 0x00000008;
873                 tel_ = value;
874                 onChanged();
875                 return this;
876             }
877 
878             /**
879              * <code>optional string tel = 4;</code>
880              */
881             public Builder clearTel() {
882                 bitField0_ = (bitField0_ & ~0x00000008);
883                 tel_ = getDefaultInstance().getTel();
884                 onChanged();
885                 return this;
886             }
887 
888             /**
889              * <code>optional string tel = 4;</code>
890              */
891             public Builder setTelBytes(com.google.protobuf.ByteString value) {
892                 if (value == null) {
893                     throw new NullPointerException();
894                 }
895                 bitField0_ |= 0x00000008;
896                 tel_ = value;
897                 onChanged();
898                 return this;
899             }
900 
901             // @@protoc_insertion_point(builder_scope:Person)
902         }
903 
904         static {
905             defaultInstance = new Person(true);
906             defaultInstance.initFields();
907         }
908 
909         // @@protoc_insertion_point(class_scope:Person)
910     }
911 
912     private static com.google.protobuf.Descriptors.Descriptor internal_static_Person_descriptor;
913     private static com.google.protobuf.GeneratedMessage.FieldAccessorTable internal_static_Person_fieldAccessorTable;
914 
915     public static com.google.protobuf.Descriptors.FileDescriptor getDescriptor() {
916         return descriptor;
917     }
918 
919     private static com.google.protobuf.Descriptors.FileDescriptor descriptor;
920     static {
921         java.lang.String[] descriptorData = {
922                 "
06person"<
06Person22

02id3001 01(032214
04name3002"
923                         + " 01(	2213
03sex3003 01(	2213
03tel3004 01(	B16B14Person"
924                         + "Probuf" };
925         com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner assigner = new com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner() {
926             public com.google.protobuf.ExtensionRegistry assignDescriptors(
927                     com.google.protobuf.Descriptors.FileDescriptor root) {
928                 descriptor = root;
929                 internal_static_Person_descriptor = getDescriptor().getMessageTypes().get(0);
930                 internal_static_Person_fieldAccessorTable = new com.google.protobuf.GeneratedMessage.FieldAccessorTable(
931                         internal_static_Person_descriptor, new java.lang.String[] { "Id", "Name", "Sex", "Tel", });
932                 return null;
933             }
934         };
935         com.google.protobuf.Descriptors.FileDescriptor.internalBuildGeneratedFileFrom(descriptorData,
936                 new com.google.protobuf.Descriptors.FileDescriptor[] {}, assigner);
937     }
938 
939     // @@protoc_insertion_point(outer_class_scope)
940 }

PersonProbuf（自动生成）

 1 public class ReqClient {
 2 
 3     public void connect(String host, int port) throws Exception {
 4         // 配置服务端的NIO线程组
 5         EventLoopGroup group = new NioEventLoopGroup();
 6 
 7         try {
 8             // Bootstrap 类，是启动NIO服务器的辅助启动类
 9             Bootstrap b = new Bootstrap();
10             b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true)
11                     .handler(new ChannelInitializer<SocketChannel>() {
12                         @Override
13                         public void initChannel(SocketChannel ch) throws Exception {
14                             // 解码器在读时才用，编码器在写时才用
15 
16                             // 解码类
17                             ch.pipeline().addLast(new ProtobufVarint32FrameDecoder());// frame解码得到ByteBuf
18                             ch.pipeline().addLast(new ProtobufDecoder(PersonProbuf.Person.getDefaultInstance()));// ByteBuf解码得到自定义的Protobuf类
19                             // 编码类
20                             ch.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
21                             ch.pipeline().addLast(new ProtobufEncoder());
22 
23                             ch.pipeline().addLast(new ReqClientHandler());
24 
25                         }
26                     });
27 
28             // 发起异步连接操作
29             ChannelFuture f = b.connect(host, port).sync();
30             System.out.println("客户端启动.");
31 
32             // 等待客服端链路关闭
33             f.channel().closeFuture().sync();
34         } finally {
35             group.shutdownGracefully();
36         }
37     }
38 
39     public static void main(String[] args) throws Exception {
40         int port = 8080;
41         if (args != null && args.length > 0) {
42             try {
43                 port = Integer.valueOf(args[0]);
44             } catch (NumberFormatException ex) {
45             }
46         }
47         new ReqClient().connect("127.0.0.1", port);
48     }
49 }

ReqClient

 1 public class ReqClientHandler extends ChannelHandlerAdapter {// 由于添加了编码器和解码器，这里输出和读入的都已是自定义的Protobuf类型
 2 
 3     @Override
 4     public void channelActive(ChannelHandlerContext ctx) {
 5         for (int i = 0; i < 2; i++) {
 6             ctx.write(request(i));
 7         }
 8         ctx.flush();
 9     }
10 
11     private PersonProbuf.Person request(int id) {
12         PersonProbuf.Person.Builder builder = PersonProbuf.Person.newBuilder();
13         builder.setId(id);
14         builder.setName("orange");
15         builder.setSex("man");
16         builder.setTel("999");
17 
18         return builder.build();
19     }
20 
21     @Override
22     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
23         System.out.println("receive server response:[" + msg + "]");
24     }
25 
26     @Override
27     public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
28         ctx.flush();
29     }
30 
31     @Override
32     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
33         cause.printStackTrace();
34         ctx.close();
35     }
36 }

ReqClientHandler

 1 public class ReqServer {
 2 
 3     public void bind(int port) throws Exception {
 4         EventLoopGroup bossGroup = new NioEventLoopGroup();
 5         EventLoopGroup WorkerGroup = new NioEventLoopGroup();
 6 
 7         try {
 8             ServerBootstrap b = new ServerBootstrap();
 9             b.group(bossGroup, WorkerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024)
10                     .childHandler(new ChannelInitializer<SocketChannel>() {
11                         @Override
12                         public void initChannel(SocketChannel ch) {
13                             // protobufDecoder仅仅负责编码，并不支持读半包，所以在之前，一定要有读半包的处理器。
14                             // 有三种方式可以选择：
15                             // 使用netty提供ProtobufVarint32FrameDecoder
16                             // 继承netty提供的通用半包处理器 LengthFieldBasedFrameDecoder
17                             // 继承ByteToMessageDecoder类，自己处理半包
18 
19                             // 解码器在读时才用，编码器在写时才用
20 
21                             // 解码类
22                             ch.pipeline().addLast(new ProtobufVarint32FrameDecoder());// frame解码得到ByteBuf
23                             ch.pipeline().addLast(new ProtobufDecoder(PersonProbuf.Person.getDefaultInstance()));// ByteBuf解码得到自定义的Protobuf类
24                             // 编码类
25                             ch.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
26                             ch.pipeline().addLast(new ProtobufEncoder());
27 
28                             ch.pipeline().addLast(new ReqServerHandler());
29                         }
30                     });
31 
32             // 绑定端口,同步等待成功
33             ChannelFuture f = b.bind(port).sync();
34             System.out.println("服务端启动.");
35             
36             // 等待服务端监听端口关闭
37             f.channel().closeFuture().sync();
38         } finally {
39             // 释放线程池资源
40             bossGroup.shutdownGracefully();
41             WorkerGroup.shutdownGracefully();
42         }
43     }
44 
45     public static void main(String[] args) throws Exception {
46         int port = 8080;
47         if (args != null && args.length > 0) {
48             try {
49                 port = Integer.valueOf(args[0]);
50             } catch (NumberFormatException ex) {
51             }
52         }
53         new ReqServer().bind(port);
54     }
55 
56 }

ReqServer

 1 public class ReqServerHandler extends ChannelHandlerAdapter {//由于添加了编码器和解码器，这里输出和读入的都已是自定义的Protobuf类型
 2     @Override
 3     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
 4         PersonProbuf.Person people = (PersonProbuf.Person) msg;
 5         if ("Orange".equalsIgnoreCase(people.getName())) {
 6             // if("Orange".equals(people.getName())){
 7             System.out.println("accept client people:[" + people.toString() + "]");
 8             ctx.writeAndFlush(response(people.getId()));
 9         }
10     }
11 
12     private PersonProbuf.Person response(long peopleID) {
13         PersonProbuf.Person.Builder builder = PersonProbuf.Person.newBuilder();
14         builder.setId(peopleID);
15         builder.setName("karl");
16         builder.setSex("boy");
17         builder.setTel("110");
18         return builder.build();
19     }
20 
21     @Override
22     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
23         cause.printStackTrace();
24         ctx.close();
25     }
26 }

ReqServerHandler

其中用到了自动生成的 PersonProbuf.java，生成方法如下：

1、从这里下载压缩包并解压。（生成各种语言的代码时需要用到相关库）.

2、从这里下载protoc.exe放在上述包的src目录下（用于根据.proto文件生产对应的java类），不妨把src目录加入到环境变量。

3、定义消息格式，person.proto（消息格式的定义规则可参看这里），如下：

1 //option java_package = "Serialization_ProtoBuf.ProtoBuf"; //写包名的话，会自动创建包名指定的文件夹并把生成的类放在其下，此外，类里属性或方法的调用会加上全限定名，移动到其他地方时难改，所以最好别加此项。
2 option java_outer_classname = "PersonProbuf"; 
3 
4 message Person {
5     optional int64 id=1; //可选的字段，为64位整数..
6     optional string name=2;
7     optional string sex=3;
8     optional string tel=4;
9 }

person.proto

4、执行 protoc.exe --java_out=java类输出目录 proto文件路径，就自动生成了对应的类文件Personprobuf.java，文件名由person.proto里的 java_outer_classname 指定（很长。。。）

其他：Protobuf生成的类的基本操作（以Personprobuf.java为例）

 1 class TestProtobuf {
 2 
 3     public static void main(String[] args) {
 4         PersonProbuf.Person.Builder builder = PersonProbuf.Person.newBuilder();
 5 
 6         builder.setId(1);
 7         builder.setName("Karl");
 8         builder.setSex("boy");
 9         builder.setTel("110");
10         PersonProbuf.Person person = builder.build();
11 
12         System.out.println(person.toString());
13 
14         System.out.println(person.toByteString());
15         System.out.println();
16 
17         byte[] buf = person.toByteArray();
18         for (byte b : buf) {
19             System.out.print(b);
20         }
21         System.out.println("
");
22 
23         try {
24             PersonProbuf.Person person2 = PersonProbuf.Person.parseFrom(buf);
25             System.out.println(person2.getName() + ", " + person2.getTel());
26         } catch (InvalidProtocolBufferException e) {
27             e.printStackTrace();
28         }
29     }
30 }
31 
32 
33 //结果
34 id: 1
35 name: "Karl"
36 sex: "boy"
37 tel: "110"
38 
39 <ByteString@31cefde0 size=18>
40 
41 81184759711410826398111121343494948
42 
43 Karl, 110

TestProtobuf

2、参考资料

1、http://mangocool.com/1446174360500.html 1.1

2、http://netty.io/wiki/user-guide-for-4.x.html 官方示例

3、http://www.yiibai.com/netty/netty-discard-server.htm 官方示例翻译

4、https://github.com/orange1438/Netty_Course/tree/master/src/main/java/Serialization_ProtoBuf 结合Protobuf

5、https://blog.csdn.net/dc_726/article/details/47912337 Netty总结

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原文地址：https://www.cnblogs.com/z-sm/p/6749843.html