Netty使用MessagePack首先自定义编解码器

在我们使用Netty开发基于网络的应用程序的时候，你都需要实现一些符合自己应用的codec，在Netty中也提供了很多编解码的抽象类，我们只需要继承这些类后，重写部分方法就可以实现decode和encode。例如在我们继承了ByteToMessageDecoder 类后只需要重写decode()方法就可以实现解码。


下面我讲结合MessagePack来实现一个编解码的demo。MessagePack是一个类似Json的序列化技术，据官方说它比json更小更快。


在这个例子中，在客户端中，MsgPackEncode在继承MessageToByteEncoder后重写了encode()方法，把Student对象编码为byte数组；在服务器端MsgPackDecode在继承MessageToMessageDecoder后重写了decode()方法，把byte数组解码成List<Object>。


客户端代码：


 

public class TimeClient {private final static int port = 28080;private final static String host = "127.0.0.1";private static EventLoopGroup group = new NioEventLoopGroup();public void createBootstrap(Bootstrap b, EventLoopGroup group) {b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch)throws Exception {ChannelPipeline pipeline = ch.pipeline();pipeline.addLast(new MsgPackDecode());pipeline.addLast(new MsgPackEncode());pipeline.addLast(new TimeClientHandle());}});try {ChannelFuture f = b.connect(host, port).sync();f.channel().closeFuture().sync();} catch (InterruptedException e) {e.printStackTrace();group.shutdownGracefully();}}public static void main(String[] args) {new TimeClient().createBootstrap(new Bootstrap(), group);}}TimeClientHandle： public class TimeClientHandle extends ChannelInboundHandlerAdapter {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {ctx.writeAndFlush(getStudent());}@Overridepublic void channelReadComplete(ChannelHandlerContext ctx) throws Exception {ctx.flush();}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)throws Exception {ctx.close();}private Student getStudent(){Student s = new Student();s.setId(3);s.setName("zhangsan");return s;}}

服务端代码：


 

public class TimeServer {public void bind(int port) {EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workGroup = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workGroup)    .channel(NioServerSocketChannel.class)    .option(ChannelOption.SO_BACKLOG, 1024).childHandler(new ChannelInitializer<SocketChannel>(){@Overrideprotected void initChannel(SocketChannel ch)throws Exception {ChannelPipeline pipeline = ch.pipeline();pipeline.addLast(new MsgPackDecode());pipeline.addLast(new MsgPackEncode());ch.pipeline().addLast(new TimeServerHandle());}});try {ChannelFuture f = b.bind(port).sync();f.channel().closeFuture().sync();} catch (InterruptedException e) {e.printStackTrace();bossGroup.shutdownGracefully();workGroup.shutdownGracefully();}}public static void main(String[] args) {int port = 28080;new TimeServer().bind(port);}}TimeSevrerHandle： public class TimeServerHandle extends ChannelInboundHandlerAdapter {@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg)throws Exception {@SuppressWarnings("unchecked")List<Student> s = (List<Student>) msg;System.out.println(s);}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)throws Exception {ctx.close();}}

其中服务端和客户端都有的Student类、MsgPackEncode、MsgPackDecode为：

Student：@Messagepublic class Student {private int id;private String name;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Student [id=" + id + ", name=" + name + "]";}}MsgPackEncode：public class MsgPackEncode extends MessageToByteEncoder<Object> {@Overrideprotected void encode(ChannelHandlerContext ctx, Object msg, ByteBuf out)throws Exception {MessagePack msgPack = new MessagePack();System.out.println(msg == null);byte[] raw = null;raw = msgPack.write(msg);out.writeBytes(raw);}}MsgPackDecode：public class MsgPackDecode extends MessageToMessageDecoder<ByteBuf>{@Overrideprotected void decode(ChannelHandlerContext ctx, ByteBuf msg,List<Object> out) throws Exception {final byte[] array;final int length = msg.readableBytes();array = new byte[length];msg.getBytes(msg.readableBytes(), array, 0, length);MessagePack msgPack = new MessagePack();out.add(msgPack.read(array));}}

服务端控制台输出为：


 


[3,"zhangsan"]
下面说一下当时踩的坑（由于之前没接触过messagepack）：


要传输的javabean一定要加上注解@message，否则会报错。
最后服务端decode后的对象是一个List<Object>（害我研究了半天，不知道为什么报错，最后还是查看的官方文档才解决的），你直接用对象去接收，会报异常org.msgpack.type.ArrayValueImpl cannot be cast to com.nettyserver.Student