Netty之实现自定义简单的编解码器二（MessageToMessageEncoder<CharSequence>和MessageToMessageDecoder<ByteBuf>）

怼烎@ 2022-07-14 15:19 382阅读 0赞

1、对于MessageToMessageEncoder的理解

MessageToMessageEncoder编码器，这里的第二个Message可以理解为任意一个对象。如果是使用ByteBuf对象的话，就和之前的MessageToByte的原理是一样的了。所以要在MessageToMessageDecoder<ByteBuf>的解码器里面，手动的指定，是对ByteBuf类型的对象进行解码的操作。

2、编写MyStringEncoder编码器和MyStringDecoder解码器，**以便于，Netty中可以直接发送和接收String类型的数据**

2.1  MyStringEncoder编码器的代码

import io.netty.buffer.ByteBufUtil;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.handler.codec.MessageToMessageEncoder;
    import java.nio.CharBuffer;
    import java.nio.charset.Charset;
    import java.util.List;
    
    public class MyStringEncoder extends MessageToMessageEncoder<CharSequence> {
    	private final Charset charset;
    
    	public MyStringEncoder() {
    		this(Charset.defaultCharset());
    	}
    
    	public MyStringEncoder(Charset charset) {
    		if (charset == null) {
    			throw new NullPointerException("charset");
    		}
    		this.charset = charset;
    	}
    
    	protected void encode(ChannelHandlerContext ctx, CharSequence msg,
    			List<Object> out) throws Exception {
    		if (msg.length() == 0) {
    			return;
    		}
    
    		out.add(ByteBufUtil.encodeString(ctx.alloc(), CharBuffer.wrap(msg),
    				this.charset));
    	}
    }

2.2  MyStringDecoder解码器的代码

import java.nio.charset.Charset;
    import java.util.List;
    import io.netty.buffer.ByteBuf;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.handler.codec.MessageToMessageDecoder;
    
    public class MyStringDecoder extends MessageToMessageDecoder<ByteBuf> {
    	private final Charset charset;
    
    	public MyStringDecoder() {
    		this(Charset.defaultCharset());
    	}
    
    	public MyStringDecoder(Charset charset) {
    		if (charset == null) {
    			throw new NullPointerException("charset");
    		}
    		this.charset = charset;
    	}
    
    	protected void decode(ChannelHandlerContext ctx, ByteBuf msg,
    			List<Object> out) throws Exception {
    		out.add(msg.toString(this.charset));
    	}
    }

3、服务端的实现

import io.netty.bootstrap.ServerBootstrap;
    import io.netty.channel.ChannelFuture;
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelOption;
    import io.netty.channel.EventLoopGroup;
    import io.netty.channel.nio.NioEventLoopGroup;
    import io.netty.channel.socket.SocketChannel;
    import io.netty.channel.socket.nio.NioServerSocketChannel;
    
    public class Server {
    	public void bind(int port) throws Exception {
    		// 服务器线程组 用于网络事件的处理 一个用于服务器接收客户端的连接
    		// 另一个线程组用于处理SocketChannel的网络读写
    		EventLoopGroup bossGroup = new NioEventLoopGroup();
    		EventLoopGroup workerGroup = new NioEventLoopGroup();
    		try {
    			// NIO服务器端的辅助启动类 降低服务器开发难度
    			ServerBootstrap serverBootstrap = new ServerBootstrap();
    			serverBootstrap.group(bossGroup, workerGroup)
    					.channel(NioServerSocketChannel.class)// 类似NIO中serverSocketChannel
    					.option(ChannelOption.SO_BACKLOG, 1024)// 配置TCP参数
    					.option(ChannelOption.SO_BACKLOG, 1024) // 设置tcp缓冲区
    					.option(ChannelOption.SO_SNDBUF, 32 * 1024) // 设置发送缓冲大小
    					.option(ChannelOption.SO_RCVBUF, 32 * 1024) // 这是接收缓冲大小
    					.option(ChannelOption.SO_KEEPALIVE, true) // 保持连接
    					.childHandler(new ChildChannelHandler());// 最后绑定I/O事件的处理类
    																// 处理网络IO事件
    
    			// 服务器启动后 绑定监听端口 同步等待成功 主要用于异步操作的通知回调 回调处理用的ChildChannelHandler
    			ChannelFuture f = serverBootstrap.bind(port).sync();
    			System.out.println("Server启动");
    			// 等待服务端监听端口关闭
    			f.channel().closeFuture().sync();
    
    		} finally {
    			// 优雅退出 释放线程池资源
    			bossGroup.shutdownGracefully();
    			workerGroup.shutdownGracefully();
    			System.out.println("服务器优雅的释放了线程资源...");
    		}
    
    	}
    
    	/**
    	 * 网络事件处理器
    	 */
    	private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
    		@Override
    		protected void initChannel(SocketChannel ch) throws Exception {
    			// 增加自定义的编码器和解码器
    			ch.pipeline().addLast(new MyStringEncoder());
    			ch.pipeline().addLast(new MyStringDecoder());
    			// 服务端的处理器
    			ch.pipeline().addLast(new ServerHandler());
    		}
    	}
    
    	public static void main(String[] args) throws Exception {
    		int port = 9998;
    		new Server().bind(port);
    	}
    }

4、服务端Handler的实现

import io.netty.channel.ChannelHandlerAdapter;
    import io.netty.channel.ChannelHandlerContext;
    
    public class ServerHandler extends ChannelHandlerAdapter {
    
    	@Override
    	public void channelRead(ChannelHandlerContext ctx, Object msg)
    			throws Exception {
    		// 接受客户端的数据
    		String body = (String) msg;
    		System.out.println("Client :" + body);
    		// 服务端，回写数据给客户端
    		// 直接回写整形的数据
    		String data = "Hello ,I am Server ...";
    		ctx.writeAndFlush(data);
    
    	}
    
    	@Override
    	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
    			throws Exception {
    		ctx.close();
    	}
    
    	@Override
    	public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
    		ctx.flush();
    	}
    }

5、 客户端的实现

import io.netty.bootstrap.Bootstrap;
    import io.netty.channel.ChannelFuture;
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelOption;
    import io.netty.channel.EventLoopGroup;
    import io.netty.channel.nio.NioEventLoopGroup;
    import io.netty.channel.socket.SocketChannel;
    import io.netty.channel.socket.nio.NioSocketChannel;
    
    public class Client {
    	/**
    	 * 连接服务器
    	 * 
    	 * @param port
    	 * @param host
    	 * @throws Exception
    	 */
    	public void connect(int port, String host) throws Exception {
    		// 配置客户端NIO线程组
    		EventLoopGroup group = new NioEventLoopGroup();
    		try {
    			// 客户端辅助启动类 对客户端配置
    			Bootstrap b = new Bootstrap();
    			b.group(group)//
    					.channel(NioSocketChannel.class)//
    					.option(ChannelOption.TCP_NODELAY, true)//
    					.handler(new MyChannelHandler());//
    			// 异步链接服务器 同步等待链接成功
    			ChannelFuture f = b.connect(host, port).sync();
    			System.out.println(f);
    			// 发送消息
    			Thread.sleep(1000);
    			f.channel().writeAndFlush("777");
    			f.channel().writeAndFlush("666");
    			Thread.sleep(2000);
    			f.channel().writeAndFlush("888");
    
    			// 等待链接关闭
    			f.channel().closeFuture().sync();
    
    		} finally {
    			group.shutdownGracefully();
    			System.out.println("客户端优雅的释放了线程资源...");
    		}
    
    	}
    
    	/**
    	 * 网络事件处理器
    	 */
    	private class MyChannelHandler extends ChannelInitializer<SocketChannel> {
    		@Override
    		protected void initChannel(SocketChannel ch) throws Exception {
    			// 增加自定义的编码器和解码器
    			ch.pipeline().addLast(new MyStringEncoder());
    			ch.pipeline().addLast(new MyStringDecoder());
    			// 客户端的处理器
    			ch.pipeline().addLast(new ClientHandler());
    		}
    
    	}
    
    	public static void main(String[] args) throws Exception {
    		new Client().connect(9998, "127.0.0.1");
    
    	}
    }

6、客户端Handler的实现

import io.netty.channel.ChannelHandlerAdapter;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.util.ReferenceCountUtil;
    
    public class ClientHandler extends ChannelHandlerAdapter {
    
    	@Override
    	public void channelRead(ChannelHandlerContext ctx, Object msg)
    			throws Exception {
    		try {
    			String body = (String) msg;
    			System.out.println("Client :" + body);
    
    			// 只是读数据，没有写数据的话
    			// 需要自己手动的释放的消息
    
    		} finally {
    			ReferenceCountUtil.release(msg);
    		}
    	}
    
    	@Override
    	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
    			throws Exception {
    		ctx.close();
    	}
    
    }

7、关于直接发送和接收String类型的编码

7.1 直接发送String类型的数据

![20161214214612014][]

7.2 直接接收String类型的数据

![20161214214622045][]

[20161214214612014]: /images/20220714/83c56fa72d4b4d14994a84db32579781.png
[20161214214622045]: /images/20220714/0223cbaf8f004069b9c57a04e6d8cbd7.png