Springboot+protobuf + Netty 传输文件，代码怎么写

以下是一个简单的示例代码，实现了Springboot+protobuf+Netty传输文件的功能：

1. 定义protobuf消息格式

syntax = "proto3";

message FileRequest {
  string fileName = 1;
}

message FileResponse {
  int32 fileSize = 1;
  bytes fileContent = 2;
}

2. 编写Netty服务端和客户端

Netty服务端：

@Component
@ChannelHandler.Sharable
public class FileServerHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
    if (msg instanceof FileRequest) {
      FileRequest request = (FileRequest) msg;
      String fileName = request.getFileName();
      File file = new File(fileName);
      if (file.exists()) {
        byte[] fileContent = Files.readAllBytes(file.toPath());
        FileResponse response = FileResponse.newBuilder()
          .setFileSize(fileContent.length)
          .setFileContent(ByteString.copyFrom(fileContent))
          .build();
        ctx.writeAndFlush(response);
      } else {
        // 文件不存在
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
      }
    } else {
      super.channelRead(ctx, msg);
    }
  }
}

Netty客户端：

@Component
public class FileClient {
  private Bootstrap bootstrap;
  private EventLoopGroup group;
  private Channel channel;

  @PostConstruct
  public void init() {
    group = new NioEventLoopGroup();
    bootstrap = new Bootstrap()
      .group(group)
      .channel(NioSocketChannel.class)
      .handler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel ch) throws Exception {
          ChannelPipeline pipeline = ch.pipeline();
          pipeline.addLast(new ProtobufVarint32LengthFieldPrepender());
          pipeline.addLast(new ProtobufEncoder());
          pipeline.addLast(new ProtobufVarint32FrameDecoder());
          pipeline.addLast(new ProtobufDecoder(FileResponse.getDefaultInstance()));
          pipeline.addLast(new FileClientHandler());
        }
      });
  }

  public void getFile(String fileName, String host, int port) throws InterruptedException {
    channel = bootstrap.connect(host, port).sync().channel();
    FileRequest request = FileRequest.newBuilder()
      .setFileName(fileName)
      .build();
    channel.writeAndFlush(request).sync();
  }

  public void close() {
    channel.close();
    group.shutdownGracefully();
  }
}

@ChannelHandler.Sharable
public class FileClientHandler extends SimpleChannelInboundHandler<FileResponse> {
  @Override
  protected void channelRead0(ChannelHandlerContext ctx, FileResponse msg) throws Exception {
    if (msg.getFileSize() > 0) {
      byte[] fileContent = msg.getFileContent().toByteArray();
      // 将文件保存到本地
      FileOutputStream fos = new FileOutputStream("local_file");
      fos.write(fileContent);
      fos.close();
    } else {
      // 文件不存在
      System.err.println("File not found.");
    }
  }
}

3. 在Springboot中使用Netty

在Springboot中，可以使用@Configuration和@Bean注解来配置和启动Netty服务端和客户端：

@Configuration
public class NettyConfig {
  @Autowired
  private FileServerHandler fileServerHandler;

  @Value("${netty.server.port}")
  private int serverPort;

  @Bean(name = "bossGroup")
  public EventLoopGroup bossGroup() {
    return new NioEventLoopGroup();
  }

  @Bean(name = "workerGroup")
  public EventLoopGroup workerGroup() {
    return new NioEventLoopGroup();
  }

  @Bean(name = "serverBootstrap")
  public ServerBootstrap serverBootstrap(@Qualifier("bossGroup") EventLoopGroup bossGroup,
                                         @Qualifier("workerGroup") EventLoopGroup workerGroup) {
    ServerBootstrap bootstrap = new ServerBootstrap();
    bootstrap.group(bossGroup, workerGroup)
      .channel(NioServerSocketChannel.class)
      .childHandler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel ch) throws Exception {
          ChannelPipeline pipeline = ch.pipeline();
          pipeline.addLast(new ProtobufVarint32FrameDecoder());
          pipeline.addLast(new ProtobufDecoder(FileRequest.getDefaultInstance()));
          pipeline.addLast(fileServerHandler);
        }
      });
    return bootstrap;
  }

  @Bean(initMethod = "bind", destroyMethod = "shutdownGracefully")
  public ChannelFuture serverChannelFuture(@Qualifier("serverBootstrap") ServerBootstrap serverBootstrap) {
    return serverBootstrap.bind(serverPort);
  }

  @Autowired
  private FileClient fileClient;

  @Value("${netty.client.host}")
  private String clientHost;

  @Value("${netty.client.port}")
  private int clientPort;

  @Bean(initMethod = "init", destroyMethod = "close")
  public FileClient fileClient() {
    return new FileClient();
  }
}

4. 实现文件传输功能

在Springboot中，可以使用@RestController注解定义一个HTTP接口，用于调用Netty客户端获取文件：

@RestController
public class FileController {
  @Autowired
  private FileClient fileClient;

  @GetMapping("/file/{fileName}")
  public String getFile(@PathVariable String fileName) {
    try {
      fileClient.getFile(fileName, "localhost", 8000);
      return "File downloaded successfully.";
    } catch (InterruptedException e) {
      e.printStackTrace();
      return "File download failed.";
    }
  }
}

这样，当调用http://localhost:8080/file/test.txt时，就可以从Netty服务端下载test.txt文件并保存到本地。