netty Bootstrap 学习例子，写在main方法

好的，以下是一个简单的 Netty Bootstrap 学习例子，写在 main 方法中：

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
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.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

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

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

    public void run() throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new NettyClientHandler());
                        }
                    });

            ChannelFuture future = bootstrap.connect(host, port).sync();
            future.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        String host = "localhost";
        int port = 8888;
        new NettyClient(host, port).run();
    }
}

class NettyClientHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        String msg = "Hello, Netty!";
        ByteBuf byteBuf = Unpooled.buffer(msg.getBytes().length);
        byteBuf.writeBytes(msg.getBytes());
        ctx.writeAndFlush(byteBuf);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf byteBuf = (ByteBuf) msg;
        byte[] bytes = new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(bytes);
        String result = new String(bytes);
        System.out.println("Received message from server: " + result);
        byteBuf.release();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

这是一个简单的 Netty 客户端，它会连接到指定的服务器地址和端口，并向服务器发送一条消息，然后等待服务器的响应。在这个例子中，我们使用了 NioEventLoopGroup 和 NioSocketChannel，具体细节可以参考 Netty 官方文档。同时，我们也实现了一个 NettyClientHandler，它会在客户端与服务器建立连接后被调用，并且会在接收到服务器的响应后被调用。