Netty-主动关闭Server

最近在实现某个功能需求的时候使用到了Netty，我们的需求需要netty的server端能实现主动关闭，而之前一直没有深入了解过，只会实现简单的连接，看了一些资料并实验后找到关闭server的方法：

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();
	}
}