java netty4+protobuf3,传输500MB大文件，详细代码怎么写？

以下是一个简单的Java Netty4 + Protobuf3示例，用于传输500MB大文件。请注意，这只是一个示例，并不是最优的解决方案，您可能需要根据您的具体需求进行调整。

服务端代码：

public class FileServer {
    private final int port;
    private final String filePath;

    public FileServer(int port, String filePath) {
        this.port = port;
        this.filePath = filePath;
    }

    public void run() throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .option(ChannelOption.SO_BACKLOG, 100)
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new ProtobufVarint32FrameDecoder());
                     ch.pipeline().addLast(new ProtobufDecoder(FileTransfer.FileRequest.getDefaultInstance()));
                     ch.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
                     ch.pipeline().addLast(new ProtobufEncoder());
                     ch.pipeline().addLast(new FileServerHandler(filePath));
                 }
             });

            // Start the server.
            ChannelFuture f = b.bind(port).sync();

            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = Integer.parseInt(args[0]);
        String filePath = args[1];
        new FileServer(port, filePath).run();
    }
}

客户端代码：

public class FileClient {
    private final String host;
    private final int port;
    private final String filePath;

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

    public void run() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.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 ProtobufVarint32FrameDecoder());
                     ch.pipeline().addLast(new ProtobufDecoder(FileTransfer.FileResponse.getDefaultInstance()));
                     ch.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
                     ch.pipeline().addLast(new ProtobufEncoder());
                     ch.pipeline().addLast(new FileClientHandler(filePath));
                 }
             });

            // Start the client.
            ChannelFuture f = b.connect(host, port).sync();

            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        String host = args[0];
        int port = Integer.parseInt(args[1]);
        String filePath = args[2];
        new FileClient(host, port, filePath).run();
    }
}

处理程序代码：

public class FileServerHandler extends SimpleChannelInboundHandler<FileTransfer.FileRequest> {
    private final String filePath;

    public FileServerHandler(String filePath) {
        this.filePath = filePath;
    }

    @Override
    public void channelRead0(ChannelHandlerContext ctx, FileTransfer.FileRequest req) throws Exception {
        long start = req.getStart();
        long end = req.getEnd();

        FileInputStream fis = new FileInputStream(filePath);
        fis.skip(start);
        byte[] bytes = new byte[(int) (end - start + 1)];
        fis.read(bytes);
        fis.close();

        FileTransfer.FileResponse.Builder builder = FileTransfer.FileResponse.newBuilder();
        builder.setBytes(ByteString.copyFrom(bytes));
        ctx.writeAndFlush(builder.build());
    }

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

public class FileClientHandler extends ChannelInboundHandlerAdapter {
    private final String filePath;

    public FileClientHandler(String filePath) {
        this.filePath = filePath;
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        try {
            File file = new File(filePath);
            long fileSize = file.length();
            long chunkSize = 1024 * 1024; // 1MB
            long start = 0;
            long end = chunkSize - 1;
            while (start < fileSize) {
                if (end >= fileSize) {
                    end = fileSize - 1;
                }
                FileTransfer.FileRequest.Builder builder = FileTransfer.FileRequest.newBuilder();
                builder.setStart(start);
                builder.setEnd(end);
                ctx.write(builder.build());
                start += chunkSize;
                end += chunkSize;
            }
            ctx.flush();
        } catch (Exception e) {
            e.printStackTrace();
            ctx.close();
        }
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        FileTransfer.FileResponse res = (FileTransfer.FileResponse) msg;
        FileOutputStream fos = new FileOutputStream("output");
        fos.write(res.getBytes().toByteArray());
        fos.close();
    }

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

这里的关键是将文件分成块，并将每个块作为独立的请求发送到服务器。服务器读取每个块，并将其作为字节流发送回客户端。客户端将字节流写入文件。

当然，这里还有很多需要优化的地方，例如考虑到网络波动、数据丢失、超时等异常情况。但是希望这个示例可以帮助您入门。