Java Netty Codecs 程序「建议收藏」

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服务端定义了一个Handler和三个Decoder。Handler接收客户端的信息，然后传递给decoder过滤处理。

1.服务端

package com.learn.netty.codecs;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.string.StringDecoder;

import java.net.InetSocketAddress;

public class Server {
    public static void main(String[] args) throws Exception {
        ServerBootstrap bootstrap = new ServerBootstrap();
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            bootstrap.group(group).channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(8888))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            socketChannel.pipeline().addFirst(new ReadHandler())
                                    .addLast(new FixedLengthDecoder())
                                    .addLast(new LoggingDecoder())
                                    .addLast(new LastDecoder());
                        }
                    });
            ChannelFuture future = bootstrap.bind().sync();
            future.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }
}

2.服务端Handler

package com.learn.netty.codecs;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ReadHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("Received: " + buf.readableBytes());
        ctx.fireChannelRead(buf);
    }
}

3.服务端 FixedLengthDecoder

客户端传递的是数字，Java中每个int类型4字节，读取转成字符串，然后传递到下一个Decoder。

package com.learn.netty.codecs;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.util.CharsetUtil;

import java.util.List;

public class FixedLengthDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) throws Exception {
        System.out.println("Fixed: " + byteBuf.readableBytes());
        StringBuilder sb = new StringBuilder();
        while (byteBuf.readableBytes() >= 4) {
            // 读取才能向后传递
            sb.append(byteBuf.readInt());
        }
        list.add(Unpooled.copiedBuffer(sb, CharsetUtil.UTF_8));
    }
}

4.服务端 LoggingDecoder

将所有信息记录下来，然后传递接收的数字并追加一个字符串。

package com.learn.netty.codecs;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.util.CharsetUtil;

import java.nio.charset.Charset;
import java.util.List;

public class LoggingDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) throws Exception {
        System.out.println("Logging: " + byteBuf.readableBytes());
        String num = "";
        while (byteBuf.isReadable()) {
            // 读取才能向后传递
            num = byteBuf.readCharSequence(byteBuf.readableBytes(), Charset.defaultCharset()).toString();
            System.out.println(num);
        }
        list.add(Unpooled.copyInt(Integer.parseInt(num)));

        ByteBuf bf = Unpooled.copiedBuffer("Netty", CharsetUtil.UTF_8);
        list.add(bf);
    }
}

5.服务端 LastDecoder

读取接收的数字和字符串。

package com.learn.netty.codecs;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;

import java.nio.charset.Charset;
import java.util.List;

public class LastDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) throws Exception {
        // Decoder没有读取会被调用多次
        // System.out.println("Last readable: " + byteBuf.readableBytes());
        // System.out.println(byteBuf.toString(Charset.defaultCharset()));

        System.out.println("Last readable: " + byteBuf.readableBytes());
        if (byteBuf.readableBytes() == 4) {
            int num = byteBuf.readInt();
            System.out.println("num: " + num);
        } else {
            ByteBuf buf = byteBuf.readBytes(byteBuf.readableBytes());
            System.out.println(buf.toString(Charset.defaultCharset()));
        }
    }
}

6.客户端

向服务端传递 6 个 int。

package com.learn.netty.codecs;


import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

import java.net.InetSocketAddress;

public class Client {
    public static void main(String[] args) throws Exception {
        Bootstrap bootstrap = new Bootstrap();
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            bootstrap.group(group);
            bootstrap.channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel socketChannel) throws Exception {
                    socketChannel.pipeline().addFirst(new ChannelInboundHandlerAdapter(){
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) throws Exception {
                            System.out.println("client active");
                            ctx.writeAndFlush(Unpooled.copyInt(1));
                            ctx.writeAndFlush(Unpooled.copyInt(2));
                            ctx.writeAndFlush(Unpooled.copyInt(3));
                            ctx.writeAndFlush(Unpooled.copyInt(4));
                            ctx.writeAndFlush(Unpooled.copyInt(5));
                            ctx.writeAndFlush(Unpooled.copyInt(6));
                        }
                    });
                }
            }).remoteAddress(new InetSocketAddress("127.0.0.1", 8888));
            ChannelFuture future = bootstrap.connect().sync();
            future.channel().close().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }
}

结果：

Received: 24
Fixed: 24
Logging: 6
123456
Last readable: 4
num: 123456
Last readable: 5
Netty

原文地址： https://www.zhblog.net/go/java/tutorial/java-netty-codecs?t=597