Java FTP下载文件 设置了被动模式 依然出现假死 假死出现之后怎么重新启动这个子线程 Springboot

如果Java FTP下载文件设置了被动模式依然出现假死，可以在出现假死时重新启动子线程来继续下载文件。以下是一种可能的实现方式：

1. 定义一个Callable接口的实现类，用于下载文件。

public class DownloadFileCallable implements Callable<Boolean> {
    private String server;
    private int port;
    private String username;
    private String password;
    private String remoteFilePath;
    private String localFilePath;
    private long restartOffset;

    public DownloadFileCallable(String server, int port, String username, String password, String remoteFilePath, String localFilePath, long restartOffset) {
        this.server = server;
        this.port = port;
        this.username = username;
        this.password = password;
        this.remoteFilePath = remoteFilePath;
        this.localFilePath = localFilePath;
        this.restartOffset = restartOffset;
    }

    @Override
    public Boolean call() throws Exception {
        FTPClient ftpClient = new FTPClient();
        try {
            ftpClient.connect(server, port);
            ftpClient.login(username, password);
            ftpClient.enterLocalPassiveMode();
            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
            if (restartOffset > 0) {
                ftpClient.setRestartOffset(restartOffset);
            }
            OutputStream outputStream = new FileOutputStream(localFilePath, true);
            InputStream inputStream = ftpClient.retrieveFileStream(remoteFilePath);
            byte[] buffer = new byte[1024];
            int len;
            while ((len = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, len);
            }
            outputStream.close();
            inputStream.close();
            boolean success = ftpClient.completePendingCommand();
            ftpClient.logout();
            ftpClient.disconnect();
            return success;
        } catch (IOException e) {
            e.printStackTrace();
            return false;
        }
    }
}

2. 在Spring Boot中定义一个ScheduledExecutorService，用于定期检查是否需要重新启动子线程。

@Configuration
public class DownloadFileScheduler {
    private ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);

    @Autowired
    private DownloadFileCallable downloadFileCallable;

    private Future<Boolean> future;

    @Value("${ftp.server}")
    private String server;

    @Value("${ftp.port}")
    private int port;

    @Value("${ftp.username}")
    private String username;

    @Value("${ftp.password}")
    private String password;

    @Value("${ftp.remoteFilePath}")
    private String remoteFilePath;

    @Value("${ftp.localFilePath}")
    private String localFilePath;

    private long restartOffset;

    @Value("${ftp.restartOffset}")
    public void setRestartOffset(long restartOffset) {
        this.restartOffset = restartOffset;
    }

    @PostConstruct
    public void start() {
        future = executorService.schedule(downloadFileCallable, 0, TimeUnit.MILLISECONDS);
        executorService.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                if (future.isDone()) {
                    try {
                        if (future.get()) {
                            System.out.println("File downloaded successfully.");
                            future = executorService.schedule(downloadFileCallable, 0, TimeUnit.MILLISECONDS);
                        } else {
                            System.out.println("File download failed.");
                            future = executorService.schedule(downloadFileCallable, 10, TimeUnit.SECONDS);
                        }
                    } catch (InterruptedException | ExecutionException e) {
                        e.printStackTrace();
                    }
                } else {
                    System.out.println("Download is still running.");
                }
            }
        }, 1, 1, TimeUnit.SECONDS);
    }

    @PreDestroy
    public void stop() {
        executorService.shutdown();
    }

    @Bean
    public DownloadFileCallable downloadFileCallable() {
        return new DownloadFileCallable(server, port, username, password, remoteFilePath, localFilePath, restartOffset);
    }
}

3. 在application.properties文件中配置FTP连接参数和下载文件路径。

ftp.server=ftp.example.com
ftp.port=21
ftp.username=ftpuser
ftp.password=ftppassword
ftp.remoteFilePath=/path/to/remote/file
ftp.localFilePath=/path/to/local/file
ftp.restartOffset=0

在上述代码中，我们使用ScheduledExecutorService定期检查下载文件的子线程是否已经完成。如果子线程已经完成，则根据下载结果来决定是否需要重新启动子线程。如果下载文件失败，则等待10秒后重新启动子线程。如果下载文件成功，则立即重新启动子线程。注意，在重新启动子线程时，需要将重启偏移量设置为0，否则可能会导致文件下载不完整。

总之，使用ScheduledExecutorService可以很方便地实现定期检查子线程的功能，从而避免Java FTP下载文件假死的问题。