netty实现http下载到浏览器

要使用Netty实现HTTP下载到浏览器，你需要编写一个HTTP服务器并在其中实现文件下载的逻辑。以下是一个基本的示例代码，可以帮助你开始：

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
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;
import io.netty.handler.codec.http.DefaultHttpResponse;
import io.netty.handler.codec.http.HttpHeaderNames;
import io.netty.handler.codec.http.HttpHeaderValues;
import io.netty.handler.codec.http.HttpMethod;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpResponseEncoder;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.HttpResponseStatus;
import io.netty.handler.codec.http.HttpVersion;
import io.netty.handler.stream.ChunkedFile;
import io.netty.handler.stream.ChunkedWriteHandler;

import java.io.File;
import java.io.RandomAccessFile;

public class HttpServer {
    private static final String FILE_PATH = "/path/to/your/file";
    private static final String FILE_NAME = "file.txt";
    private static final int PORT = 8080;

    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 ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline p = ch.pipeline();
                            p.addLast(new HttpServerCodec());
                            p.addLast(new HttpObjectAggregator(512 * 1024));
                            p.addLast(new ChunkedWriteHandler());
                            p.addLast(new HttpServerHandler());
                        }
                    });

            ChannelFuture f = b.bind(PORT).sync();
            System.out.println("HTTP server started on port " + PORT);

            f.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    static class HttpServerHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            if (msg instanceof io.netty.handler.codec.http.HttpRequest) {
                io.netty.handler.codec.http.HttpRequest req = (io.netty.handler.codec.http.HttpRequest) msg;

                if (req.method() == HttpMethod.GET) {
                    RandomAccessFile raf = new RandomAccessFile(new File(FILE_PATH + FILE_NAME), "r");
                    long fileLength = raf.length();

                    DefaultHttpResponse response = new DefaultHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
                    response.headers().set(HttpHeaderNames.CONTENT_TYPE, "application/octet-stream");
                    response.headers().set(HttpHeaderNames.CONTENT_DISPOSITION, "attachment; filename=\"" + FILE_NAME + "\"");
                    response.headers().set(HttpHeaderNames.CONTENT_LENGTH, String.valueOf(fileLength));
                    response.headers().set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);

                    ctx.write(response);

                    ChannelFuture sendFileFuture = ctx.write(new ChunkedFile(raf.getChannel()), ctx.newProgressivePromise());
                    sendFileFuture.addListener(new ChannelFutureListener() {
                        @Override
                        public void operationComplete(ChannelFuture future) throws Exception {
                            raf.close();
                        }
                    });

                    ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
                } else {
                    ctx.writeAndFlush(new DefaultHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.METHOD_NOT_ALLOWED))
                            .addListener(ChannelFutureListener.CLOSE);
                }
            }
        }

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

在这个示例中，我们创建了一个HTTP服务器，监听8080端口。当收到GET请求时，我们使用RandomAccessFile读取文件并将其发送给浏览器。注意，我们使用ChunkedFile和ChunkedWriteHandler来处理大文件的传输。

你可以将FILE_PATH和FILE_NAME替换为你自己的文件路径和文件名。启动服务器后，打开浏览器，输入http://localhost:8080/，应该会下载文件到你的本地计算机。