Spring SFTP : Unable to rename .writing file

I am using Spring SFTP integration to transfer the file and many time I got this error. It seems two threads are trying to transfer same file and conflict with each other

>2020-08-03 08:31:55,766 INF [task-scheduler-8 ] o.s.i.ftp.session.FtpSession - File has been successfully transferred from: ./abc.ext.200803
<br>
>2020-08-03 08:31:55,849 INF [task-scheduler-7 ] o.s.i.ftp.session.FtpSession - File has been successfully transferred from: ./abc.ext.200803<br>
>2020-08-03 08:31:55,850 INF [task-scheduler-7 ] .s.i.f.i.FtpInboundFileSynchronizer - Cannot rename '/local/download/abc.ext.200803.writing' to local file '/local/download/abc.ext.200803' after deleting. The local file may be busy in some other process.<br>

Is there a way so both threads should not interfere with each other?

I am using following code -

@Bean
public SftpInboundFileSynchronizer ftpInboundFileSynchronizer() {
	isFTPSessionOK();
	SftpInboundFileSynchronizer fileSynchronizer = new SftpInboundFileSynchronizer(sftpSessionFactory());

	fileSynchronizer.setPreserveTimestamp(true);
	fileSynchronizer.setRemoteDirectory(remoteDirectory);
	fileSynchronizer.setDeleteRemoteFiles(false);

	fileSynchronizer.setFilter(new SFTPLastModifiedFileFilter(remoteFileFilter));
	return fileSynchronizer;
}

private boolean isFTPSessionOK() {
	try {
		SessionFactory<LsEntry> ftpSessionFactory = sftpSessionFactory();
		boolean open = ftpSessionFactory.getSession().isOpen();
		LOG.info("FTPSession is good ? " + open);
		return open;
	} catch (Exception e) {
		LOG.error("FTPSession is not good because of error : " + e);
	}
	return false;
}

@Bean
public SessionFactory<LsEntry> sftpSessionFactory() {
	DefaultSftpSessionFactory sf = new DefaultSftpSessionFactory();
	sf.setHost(server);
	sf.setPort(port);
	sf.setUser(username);
	sf.setPassword(password);
	sf.setAllowUnknownKeys(true);
	return new CachingSessionFactory<LsEntry>(sf);
}

@Bean
@InboundChannelAdapter(channel = "sftpChannel", poller = @Poller(fixedDelay = "${${project.name}.ftp.poller.delay:600000}", maxMessagesPerPoll = "1"))
public MessageSource<File> ftpMessageSource() {
	SftpInboundFileSynchronizingMessageSource source = new SftpInboundFileSynchronizingMessageSource(ftpInboundFileSynchronizer());
	source.setLocalDirectory(new File(localFtpDirectory));
	source.setAutoCreateLocalDirectory(true);		
	return source;
}

@Bean
@ServiceActivator(inputChannel = "sftpChannel")
public MessageHandler ftpHandler() {
	return new MessageHandler() {

		@Override
		public void handleMessage(Message<?> message) throws MessagingException {
			LOG.info("File '{}' is ready for reading after SFTP", message.getPayload());
		}
	};
}

You have only this for filtering:

fileSynchronizer.setFilter(new SFTPLastModifiedFileFilter(remoteFileFilter));

but what about a filter which is going to prevent duplicates on subsequent poll?

See AcceptOnceFileListFilter. And together with that SFTPLastModifiedFileFilter you should use a ChainFileListFilter.

See docs for more info:

https://docs.spring.io/spring-integration/docs/current/reference/html/sftp.html#sftp-inbound

https://docs.spring.io/spring-integration/docs/current/reference/html/file.html#file-reading