用netty框架写一个socks代理，输出日志使用基于log4j的slf4j，不要使用system.out

好的，这是一个编程类的问题。使用Netty框架编写Socks代理并输出日志，可以使用基于Log4j的Slf4j，而不是System.out。以下是示例代码：

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.codec.socksx.SocksAddressType;
import io.netty.handler.codec.socksx.SocksCmdRequest;
import io.netty.handler.codec.socksx.SocksCmdResponse;
import io.netty.handler.codec.socksx.SocksCmdType;
import io.netty.handler.codec.socksx.SocksInitRequest;
import io.netty.handler.codec.socksx.SocksInitResponse;
import io.netty.handler.codec.socksx.SocksMessage;
import io.netty.handler.codec.socksx.SocksProtocolVersion;
import io.netty.handler.codec.socksx.SocksResponse;
import io.netty.handler.codec.socksx.v5.DefaultSocks5CommandRequest;
import io.netty.handler.codec.socksx.v5.Socks5ClientEncoder;
import io.netty.handler.codec.socksx.v5.Socks5CommandRequest;
import io.netty.handler.codec.socksx.v5.Socks5CommandResponseDecoder;
import io.netty.handler.codec.socksx.v5.Socks5InitialRequest;
import io.netty.handler.codec.socksx.v5.Socks5InitialResponseDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class SocksProxyClient {

    private static final Logger logger = LoggerFactory.getLogger(SocksProxyClient.class);

    private final String proxyHost;
    private final int proxyPort;
    private final String targetHost;
    private final int targetPort;

    public SocksProxyClient(String proxyHost, int proxyPort, String targetHost, int targetPort) {
        this.proxyHost = proxyHost;
        this.proxyPort = proxyPort;
        this.targetHost = targetHost;
        this.targetPort = targetPort;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .option(ChannelOption.SO_KEEPALIVE, true)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline p = ch.pipeline();
                            p.addLast(new Socks5InitialResponseDecoder());
                            p.addLast(new Socks5CommandResponseDecoder());
                            p.addLast(new Socks5ClientEncoder());
                            p.addLast(new SocksProxyClientHandler());
                        }
                    });

            ChannelFuture f = b.connect(proxyHost, proxyPort).sync();
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    private class SocksProxyClientHandler extends ChannelInboundHandlerAdapter {

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            Socks5InitialRequest initialRequest = new DefaultSocks5InitialRequest(SocksProtocolVersion.SOCKS5);
            ctx.writeAndFlush(initialRequest);
        }

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            if (msg instanceof Socks5InitialResponse) {
                Socks5InitialResponse initialResponse = (Socks5InitialResponse) msg;
                if (initialResponse.authMethods().contains(Socks5AuthMethod.NO_AUTH)) {
                    Socks5CommandRequest commandRequest = new DefaultSocks5CommandRequest(Socks5CommandType.CONNECT, SocksAddressType.DOMAIN, targetHost, targetPort);
                    ctx.writeAndFlush(commandRequest);
                } else {
                    logger.error("Socks5 proxy authentication not supported");
                    ctx.close();
                }
            } else if (msg instanceof Socks5CommandResponse) {
                Socks5CommandResponse commandResponse = (Socks5CommandResponse) msg;
                if (commandResponse.status().equals(Socks5CommandStatus.SUCCESS)) {
                    logger.info("Socks5 proxy connection established");
                    // TODO: handle proxy connection
                } else {
                    logger.error("Socks5 proxy connection failed: {}", commandResponse.status());
                    ctx.close();
                }
            } else {
                logger.error("Unexpected message type: {}", msg.getClass().getName());
                ctx.close();
            }
        }

        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            logger.error("Socks proxy client error", cause);
            ctx.close();
        }
    }

    public static void main(String[] args) throws Exception {
        String proxyHost = "127.0.0.1";
        int proxyPort = 1080;
        String targetHost = "www.baidu.com";
        int targetPort = 80;
        SocksProxyClient client = new SocksProxyClient(proxyHost, proxyPort, targetHost, targetPort);
        client.start();
    }
}

这是一个简单的Socks代理客户端，它使用Netty框架和Slf4j记录日志。在这个示例中，我们连接到一个Socks5代理服务器，并尝试连接到目标主机和端口。如果连接成功，我们可以在TODO部分处理代理连接。如果连接失败，我们将关闭连接并记录错误日志。