Netty Handler的调用机制

最新推荐文章于 2024-04-24 14:30:00 发布

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文章展示了如何使用Netty框架中的NettyLongToByteEncoder和NettyByteToLongDecoder进行数据编码和解码。NettyServer和NettyClient分别实现了服务端和客户端，通过NettyServerInitializer和NettyClientInitializer配置了ChannelPipeline，确保消息在传输过程中正确编码和解码。在处理消息时，注意编码器和解码器的消息类型匹配，以及ByteBuf的可读字节判断，以保证数据完整传输。

NettyLongToByteEncoder：

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

public class NettyLongToByteEncoder extends MessageToByteEncoder<Long> {
    @Override
    protected void encode(ChannelHandlerContext channelHandlerContext, Long aLong, ByteBuf byteBuf) throws Exception {
        System.out.println("NettyLongToByteEncoder encode 被调用");
        System.out.println("msg = " + aLong);
        byteBuf.writeLong(aLong);
    }
}

NettyByteToLongDecoder:

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

import java.util.List;

public class NettyByteToLongDecoder extends ByteToMessageDecoder {
    /**
     * abcdabcdabcdabcd 会根据接收到的数据，被调用多次, 知道确定没有新的元素被添加到list 或者 ByteBuf 没有更多的可读字节为止
     * 如果 list 的不为空，就会将 list 的内容传递给下一个 channelInboundhandler处理，该处理器的方法也会被调用多次
     * @param channelHandlerContext 上下文对象
     * @param byteBuf 入站的 byteBuf
     * @param list 将解码后的数据传递给下一个 handler
     * @throws Exception
     */
    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) throws Exception {
        System.out.println("NettyByteToLongDecoder 被调用");
        // 因为 Long 8个字节
        if (byteBuf.readableBytes() >= 8) {
            list.add(byteBuf.readLong());
        }
    }
}

NettyServer：


import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup bossGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new NettyServerInitializer());

            ChannelFuture channelFuture = serverBootstrap.bind(9527).sync();
            channelFuture.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

NettyServerHandler:

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

public class NettyServerHandler extends SimpleChannelInboundHandler<Long> {
    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, Long aLong) throws Exception {
        System.out.println("从客户端" + channelHandlerContext.channel().remoteAddress() + " 读取到Long" + aLong);

        // 给客户端发送一个 Long
        channelHandlerContext.writeAndFlush(4396L);
    }


    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

NettyServerInitializer:

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;

public class NettyServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline pipeline = socketChannel.pipeline();

        // 入站的 handler 进行解码
        pipeline.addLast(new NettyByteToLongDecoder());
        // 出站的 handler 进行编码，  入站 和 出站 两条线进行走
        pipeline.addLast(new NettyLongToByteEncoder());
        // 自定义的 handler 处理业务逻辑
        pipeline.addLast(new NettyServerHandler());
    }
}

NettyClient:

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class NettyClient {

    public static void main(String[] args) throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group).channel(NioSocketChannel.class).handler(new NettyClientInitializer());

            ChannelFuture channelFuture = bootstrap.connect("localhost", 9527).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            group.shutdownGracefully();
        }

    }
}

NettyClientHandler:

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

public class NettyClientHandler extends SimpleChannelInboundHandler<Long> {

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, Long aLong) throws Exception {
        System.out.println("服务器的ip=" + channelHandlerContext.channel().remoteAddress());
        System.out.println("收到服务器消息=" + aLong);
    }


    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("NettyClientHandler 发送数据");

         ctx.writeAndFlush(9527L);
        /**
         * abcdabcdabcd 16个字节
         * 该处理器的前一个 handler 是 NettyLongToByteEncoder
         * NettyLongToByteEncoder 的父类是 MessageToByteEncoder
         * 在编写 encoder 时, 要注意传入的数据类型和处理的数据类型一致
         */
        //ctx.writeAndFlush(Unpooled.copiedBuffer("abcdabcdabcdabcd", CharsetUtil.UTF_8));
    }
}

NettyClientInitializer:

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;

public class NettyClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline pipeline = socketChannel.pipeline();

        // 加入一个 出站的 handler 对数据进行编码
        pipeline.addLast(new NettyLongToByteEncoder());

        // 这是一个入站的解码器(handler)
        pipeline.addLast(new NettyByteToLongDecoder());

        // 加入一个自定义的 handler， 处理业务逻辑
        pipeline.addLast(new NettyClientHandler());
    }
}

MessageToByteEncoder 的 write 方法：

public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        ByteBuf buf = null;

        try {
            if (this.acceptOutboundMessage(msg)) { // 判断当前 msg， 是不是该处理的类型
                I cast = msg;
                buf = this.allocateBuffer(ctx, msg, this.preferDirect);

                try {
                    this.encode(ctx, cast, buf);
                } finally {
                    ReferenceCountUtil.release(msg);
                }

                if (buf.isReadable()) {
                    ctx.write(buf, promise);
                } else {
                    buf.release();
                    ctx.write(Unpooled.EMPTY_BUFFER, promise);
                }

                buf = null;
            } else { // 直接发送
                ctx.write(msg, promise);
            }
        } catch (EncoderException var17) {
            throw var17;
        } catch (Throwable var18) {
            throw new EncoderException(var18);
        } finally {
            if (buf != null) {
                buf.release();
            }

        }

    }

结论：