面试题：网络编程中Netty如何处理常见I/O异常

Netty处理常见I/O异常的机制

ChannelHandler的exceptionCaught方法：Netty通过在ChannelHandler中提供exceptionCaught方法来处理在ChannelPipeline中传播的异常。当I/O操作发生异常时，异常会被传递到ChannelPipeline，并调用各个ChannelHandler的exceptionCaught方法。可以在该方法中进行日志记录、关闭连接、重连等操作。
IdleStateHandler：用于处理连接超时。它可以设置读空闲时间、写空闲时间以及所有类型空闲时间，当达到设定的空闲时间时，会触发IdleStateEvent事件，用户可以在对应的ChannelHandler中处理该事件，例如关闭连接或发起重连。
超时设置：在Bootstrap或ServerBootstrap中可以设置连接超时时间，如bootstrap.connect(InetSocketAddress("127.0.0.1", 8080)).sync().channel().closeFuture().sync();中的连接操作就会在设定的超时时间内尝试连接，如果超时未连接成功则抛出异常。

捕获和处理连接超时异常的实际代码示例

服务端代码

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class NettyServer {
    private int port;

    public NettyServer(int port) {
        this.port = port;
    }

    public void run() throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                   .channel(NioServerSocketChannel.class)
                   .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            // 这里添加业务处理器
                        }
                    });

            ChannelFuture f = b.bind(port).sync();
            System.out.println("Server started, listening on port " + port);
            f.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        new NettyServer(8080).run();
    }
}

客户端代码

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.timeout.ConnectTimeoutHandler;

import java.util.concurrent.TimeUnit;

public class NettyClient {
    private String host;
    private int port;

    public NettyClient(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void run() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                   .channel(NioSocketChannel.class)
                   .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast(new ConnectTimeoutHandler(5, TimeUnit.SECONDS)); // 设置连接超时为5秒
                            // 这里添加业务处理器
                        }
                    });

            ChannelFuture f = b.connect(host, port).sync();
            System.out.println("Client connected to server");
            f.channel().closeFuture().sync();
        } catch (Exception e) {
            if (e instanceof java.util.concurrent.TimeoutException) {
                System.out.println("Connection timed out");
            } else {
                e.printStackTrace();
            }
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        new NettyClient("127.0.0.1", 8080).run();
    }
}

在上述客户端代码中，通过pipeline.addLast(new ConnectTimeoutHandler(5, TimeUnit.SECONDS));设置了连接超时为5秒，当连接超过5秒未成功时，会抛出java.util.concurrent.TimeoutException，在catch块中可以捕获并处理该异常，这里简单打印了连接超时信息。

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面试题：网络编程中Netty如何处理常见I/O异常

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面试题答案

Netty处理常见I/O异常的机制

捕获和处理连接超时异常的实际代码示例