Netty-主动关闭Server

　　工作中要能主动地关闭netty server端，下面的文章中的方法是好用的，记录一下。

　　原文地址：https://blog.csdn.net/wk52525/article/details/87896075

　　1.主动关闭server

• 如下面的代码所示，这里启动server时将ServerChannel的实例保存至静态属性，然后暴露一个closeServer()方法，直接调用ServerChannel的close()方法，此线程则会从阻塞状态恢复，向下执行，进入finally代码块，退出server并清理相关资源。

package com.huoli.mj.rpc.server;
 
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 org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
public class NettyServer {
 
    private static Logger logger = LoggerFactory.getLogger(NettyServer.class);
    
    private static Channel serverChannel;
 
    /** 关闭当前server */
    public static void closeServer() {
        if (serverChannel != null) {
            logger.info("close server");
            serverChannel.close();
            serverChannel = null;
        }
    }
 
    /** 启动server */
    private void start(int port) throws Exception {
        // 通过独立线程启动server
        Thread nettyServer = new Thread(() -> {
            EventLoopGroup bossGroup = new NioEventLoopGroup();
            EventLoopGroup workerGroup = new NioEventLoopGroup();
            try {
                ServerBootstrap b = new ServerBootstrap();
                b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
                        .childHandler(new DefaultServerChannelInitializer()).option(ChannelOption.SO_BACKLOG, 128)
                        .childOption(ChannelOption.SO_KEEPALIVE, true);
 
                // 绑定端口启动成功
                ChannelFuture channelFuture = b.bind(port).sync();
                logger.info("start rpc server success with port:" + port);
                // 将ServerChannel保存下来
                serverChannel = channelFuture.channel();
                // 阻塞至channel关闭
                serverChannel.closeFuture().sync();
            } catch (Exception e) {
                logger.error("MJ netty server error", e);
            } finally {
                // 优雅关闭server线程及相关资源
                workerGroup.shutdownGracefully();
                bossGroup.shutdownGracefully();
            }
        });
        nettyServer.setName("netty-server-thread");
        nettyServer.setDaemon(true);
        nettyServer.start();
    }
}

　　2.在ChannelHandler中关闭server

• 在某些场景下，会需要在特定事件回调时主动关闭server端。下面代码展示了在监听到异常抛出事件时主动关闭server的操作。
• 以下面代码为例：ChannelHandler的事件回调方法中，ctx.close() 或 ctx.channel().close()只能关闭与某个客户端连接的channel，而ctx.channel().parent()获取到的是ServerChannel，所以调用ctx.channel().parent().close()才能关闭server，使server启动线程从阻塞状态恢复，从而在finally代码块中执行退出关闭操作。

package top.kylewang.netty.demo.second.server;
 
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
public class TestSocketServerHandler extends ChannelInboundHandlerAdapter {
 
    private static final Logger logger = LoggerFactory.getLogger(TestSocketServerHandler.class);
 
    /** 监听异常 */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        // 关闭serverChannel
        ctx.channel().parent().close();
    }