Netty（22）如何实现基于Netty的HTTP客户端和服务器？

实现基于Netty的HTTP客户端和服务器，您需要分别配置服务器和客户端的引导程序、管道处理器以及相关的处理逻辑。以下是详细的步骤和代码示例：

实现基于Netty的HTTP服务器

1. 创建HTTP服务器引导程序（ServerBootstrap）：

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class HttpServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new HttpServerInitializer());

            b.bind(8080).sync().channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

2. 实现HttpServerInitializer：

import io.netty.channel.ChannelInitializer;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.HttpServerExpectContinueHandler;

public class HttpServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ch.pipeline().addLast(new HttpServerCodec());
        ch.pipeline().addLast(new HttpObjectAggregator(512 * 1024));
        ch.pipeline().addLast(new HttpServerExpectContinueHandler());
        ch.pipeline().addLast(new HttpServerHandler());
    }
}

3. 实现HttpServerHandler：

import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.*;

import static io.netty.handler.codec.http.HttpResponseStatus.OK;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;

public class HttpServerHandler extends SimpleChannelInboundHandler<FullHttpRequest> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest req) throws Exception {
        boolean keepAlive = HttpUtil.isKeepAlive(req);
        FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK);
        response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain; charset=UTF-8");

        response.content().writeBytes("Hello, World".getBytes());

        if (keepAlive) {
            response.headers().set(HttpHeaderNames.CONTENT_LENGTH, response.content().readableBytes());
            response.headers().set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);
            ctx.writeAndFlush(response);
        } else {
            ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
        }
    }
}

实现基于Netty的HTTP客户端

1. 创建HTTP客户端引导程序（Bootstrap）：

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class HttpClient {
    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
             .channel(NioSocketChannel.class)
             .handler(new HttpClientInitializer());

            b.connect("localhost", 8080).sync().channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

2. 实现HttpClientInitializer：

import io.netty.channel.ChannelInitializer;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.http.HttpClientCodec;
import io.netty.handler.codec.http.HttpObjectAggregator;

public class HttpClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ch.pipeline().addLast(new HttpClientCodec());
        ch.pipeline().addLast(new HttpObjectAggregator(512 * 1024));
        ch.pipeline().addLast(new HttpClientHandler());
    }
}

3. 实现HttpClientHandler：

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.*;

import static io.netty.handler.codec.http.HttpMethod.GET;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;

public class HttpClientHandler extends SimpleChannelInboundHandler<FullHttpResponse> {

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        FullHttpRequest request = new DefaultFullHttpRequest(HTTP_1_1, GET, "/");
        request.headers().set(HttpHeaderNames.HOST, "localhost");
        request.headers().set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);
        ctx.writeAndFlush(request);
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, FullHttpResponse response) {
        System.out.println("Response received: " + response.content().toString(io.netty.util.CharsetUtil.UTF_8));
    }

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

通过以上步骤，您可以实现一个基于Netty的HTTP服务器和客户端。服务器监听在8080端口，客户端连接到服务器并发送HTTP请求。服务器接收到请求后，返回一个简单的 "Hello, World" 响应。客户端接收到服务器的响应后，打印出响应内容。