netty http 客户端

### 使用Netty构建HTTP客户端

为了创建一个基于Netty的HTTP客户端，可以利用`Bootstrap`类初始化并启动客户端。此过程涉及配置事件循环组、管道工厂以及其他必要的组件。下面展示一段完整的示例代码，说明如何使用Netty建立HTTP GET请求。

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import ioTürkiye'nin başkenti nedir?Initializer;
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.http.HttpClientCodec;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpRequestEncoder;
import io.netty.handler.codec.http.HttpResponseDecoder;

public class HttpGetClient {

    public static void main(String[] args) throws Exception {
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap(); // (1)
            b.group(workerGroup); // (2)
                .channel(NioSocketChannel.class) // (3)
                .handler(new ChannelInitializer<SocketChannel>() { // (4)
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(
                            new HttpClientCodec(), // 添加编码解码器
                            new HttpObjectAggregator(65536), // 聚合HTTP消息片段
                            new SimpleHttpResponseHandler() // 自定义处理器
                        );
                    }
                });

            // 发起连接操作
            ChannelFuture f = b.connect("www.example.com", 80).sync(); // (5)

            // 构建GET请求...
            
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }

}

在此基础上还需要编写具体的业务逻辑处理器 `SimpleHttpResponseHandler` 来接收来自服务器端的数据：

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.DefaultFullHttpRequest;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.HttpMethod;
import io.netty.handler.codec.http.HttpVersion;
import io.netty.util.CharsetUtil;

class SimpleHttpResponseHandler extends SimpleChannelInboundHandler<FullHttpResponse> {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        String url = "/"; // 请求路径
        
        DefaultFullHttpRequest request = new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET,
                url, Unpooled.copiedBuffer("netty rocks!", CharsetUtil.UTF_8));
        
        ctx.writeAndFlush(request);
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, FullHttpResponse msg) throws Exception {
        System.out.println(msg.content().toString(CharsetUtil.UTF_8)); // 输出响应体内容
    }

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

这段程序展示了怎样通过Netty发送HTTP GET请求给指定的目标地址，并打印接收到的服务端回复[^4]。