netty4 服务端同步客户端返回的结果

 netty是一个异步通信框架，在有的时候我们想使用服务端向客户端发送消息，服务端同步等待客户端返回结果然进行下一步的业务逻辑操作。那要怎么做才能同步获取客户端返回的数据呢？这里我用到了JDK中的闭锁等待 CountDownLatch，接下来看看代码如何实现：

服务端：

package com.example.demo.server;

import com.example.demo.cache.ChannelMap;
import com.example.demo.model.Result;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import lombok.extern.slf4j.Slf4j;

/**
 * @ClassName: NettyServer
 * @Author: huangzf
 * @Date: 2018/9/25 15:40
 * @Description:
 */
@Slf4j
public class NettyServer {

    private NettyServerChannelInitializer serverChannelInitializer = null;

    private int port = 8000;


    public void bind() throws Exception {
        //配置服务端的NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            serverChannelInitializer = new NettyServerChannelInitializer();
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class)
                //保持长连接
                .childOption(ChannelOption.SO_KEEPALIVE,true)
                .option(ChannelOption.SO_BACKLOG, 1024)
                .childHandler(serverChannelInitializer);

            //绑定端口，同步等待成功
            ChannelFuture f = b.bind(port).sync();


            //等待服务器监听端口关闭
            f.channel().closeFuture().sync();
        } finally {
            //释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public Result write(Object obj, String tenantId ,String uniId) throws Exception {
        // 获取锁
        Lock lock = ChannelMap.getChannelLock(tenantId);
        try {
            Channel channel = ChannelMap.getChannel(tenantId);
            if(channel != null){
                lock.lock();
                if(channel.isOpen()){
                    // 设置同步
                    CountDownLatch latch = new CountDownLatch(1);
                    NettyServerHandler nettyServerHandler = (NettyServerHandler) channel.pipeline().get("handler");
                    nettyServerHandler.resetSync(latch,1);
                    nettyServerHandler.setUnidId(uniId);
                    channel.writeAndFlush(obj );
                    //同步返回结果
                    if (latch.await(60,TimeUnit.SECONDS)){
                        // printerServerHandler.setTimeout(0);
                        return nettyServerHandler.getResult();
                    }
                    //如果超时，将超时标志设置为1
                    //printerServerHandler.setTimeout(1);
                    log.error("请求超时60s");
                    return new Result(2,"请求超时",null);
                }else{
                    return new Result(0,"客户端已关闭!",null);
                }
            }

        }catch (Exception e){
            e.printStackTrace();
            return new Result(0,"服务出错!",null);

        }finally {
            if (lock != null){
                lock.unlock();
            }
        }
        return new Result(0,"客户端没有连接!",null);
    }

    public static void main(String[] args) throws Exception {
       new  NettyServer().bind();
    }

}

代码中write方法是业务代码调用服务端向客户端发送信息的统一入口，这里用了Lock是为了防止并发操作影响数据返回的问题，这里每个客户端通道分配一个锁。latch.await(60,TimeUnit.SECONDS) 是为了阻塞程序，等待客户端返回结果，如果60s内没有返回结果则释放锁并返回请求超时。

服务端NettyServerChannelInitializer 的实现

package com.example.demo.server;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.serialization.ClassResolvers;
import io.netty.handler.codec.serialization.ObjectDecoder;
import io.netty.handler.codec.serialization.ObjectEncoder;
import io.netty.handler.timeout.IdleStateHandler;
import java.util.concurrent.TimeUnit;

/**
 * @ClassName: NettyServerChannelInitializer
 * @Author: huangzf
 * @Date: 2018/9/25 15:43
 * @Description:
 */
public class NettyServerChannelInitializer extends ChannelInitializer {

    private NettyServerHandler handler ;



    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline pipeline = socketChannel.pipeline();
        pipeline.addLast("decoder", new ObjectDecoder(Integer.MAX_VALUE,ClassResolvers
            .weakCachingConcurrentResolver(this.getClass().getClassLoader())));
        pipeline.addLast("encoder", new ObjectEncoder());
        pipeline.addLast(new IdleStateHandler(40,0,0,TimeUnit.SECONDS));
        //服务器的逻辑
        handler = new NettyServerHandler();
        pipeline.addLast("handler", handler);
    }
}

这里使用了对象进行数据传输，避免了客户端重新解析组装对象的麻烦

package com.example.demo.server;

import com.example.demo.cache.ChannelMap;
import com.example.demo.model.Result;
import com.example.demo.model.Tenant;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.locks.ReentrantLock;
import lombok.extern.slf4j.Slf4j;

/**
 * @ClassName: NettyServerHandler
 * @Author: huangzf
 * @Date: 2018/9/25 15:44
 * @Description:
 */
@Slf4j
public class NettyServerHandler extends SimpleChannelInboundHandler {

    private CountDownLatch latch;

    /**
     * 消息的唯一ID
     */
    private String unidId = "";
    /**
     * 同步标志
     */
    private int rec;
    /**
     * 客户端返回的结果
     */
    private Result result;
    /**
     * 心跳丢失次数
     */
    private int counter = 0;


    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("Client say : " + msg.toString());
        if(msg instanceof Tenant){
            ChannelMap.setChannel(((Tenant) msg).getTenantId(),ctx.channel());
            ChannelMap.setChannelLock(((Tenant) msg).getTenantId(),new ReentrantLock());
        }

        counter = 0;
        if(rec == 1  && msg instanceof Result){
            Result re = (Result) msg;
            //校验返回的信息是否是同一个信息
            if (unidId.equals(re.getUniId())){
                latch.countDown();//消息返回完毕，释放同步锁，具体业务需要判断指令是否匹配
                rec = 0;
                result = re;
            }

        }


    }


    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        log.info("RemoteAddress : " + ctx.channel().remoteAddress().toString()+ " active !");
        super.channelActive(ctx);
    }


    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if (evt instanceof IdleStateEvent) {
            IdleStateEvent event = (IdleStateEvent) evt;
            if (event.state().equals(IdleState.READER_IDLE)){
                // 空闲40s之后触发 (心跳包丢失)
                if (counter >= 3) {
                    // 连续丢失3个心跳包 (断开连接)
                    ctx.channel().close().sync();
                    log.error("已与"+ctx.channel().remoteAddress()+"断开连接");
                    System.out.println("已与"+ctx.channel().remoteAddress()+"断开连接");
                } else {
                    counter++;
                    log.debug(ctx.channel().remoteAddress() + "丢失了第 " + counter + " 个心跳包");
                    System.out.println("丢失了第 " + counter + " 个心跳包");
                }
            }

        }
    }

    public void resetSync(CountDownLatch latch, int rec) {
        this.latch = latch;
        this.rec = rec;
    }

    public void setUnidId(String s){
        this.unidId = s;
    }

    public Result getResult() {
        return result;
    }
}

在channelRead0方法中 如果读取到的信息是Tenant （客户端刚连接上发送的消息）就为该客户端关联一个唯一标志和分配一个锁Lock（用于并发操作）

如果读取到的信息是Result（客户端响服务端的消息）就判断其是否是同一个消息（服务端发送的消息中带有该消息的唯一id，客户端返回时也要带上该id），如果是就latch.countDown() 释放同步锁，这样就可以使得服务端同步得到客户端返回的消息了。

 

详情与客户端代码请移步码云：

https://gitee.com/hzf1993/nettydemo/tree/master/sync-netty