Netty之自定义编码器MessageToMessageEncoder类-优快云博客

本文介绍了如何在Netty中实现字符串数据的编码与解码，包括自定义编码器MyStringEncoder和解码器MyStringDecoder的具体实现。此外，还详细展示了服务端与客户端的实现过程，以及如何通过这些组件实现字符串数据的发送与接收。

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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

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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));
}
}

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

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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));
}
}

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

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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);
}
}

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

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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();
}
}

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

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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”);
}
}

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

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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();
}
}

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