Spring-Integration , Upload File to SFTP remote server - java.lang.OutOfMemoryError: Direct buffer memory

In my SpringBoot application, I have used Spring Integration for uploading files to a remote SFTP server.
Below is the code snippet I have used to transfer file to SFTP server.

protected String transfer(String downloadDirectory) {
        File[] files = new File(downloadDirectory).listFiles();
        byte[] payload = null;
        String path = null;
        try {

            path = getSftpPath(downloadDirectory);
            for (int i = 0; i < files.length; i++) {
                if (files[i].isFile()) {
                    payload = Files.readAllBytes(Paths.get(files[i].toURI()));
                    gateway.upload(payload, files[i].getName(), path);
                }
            }
        } catch (Exception e) {

            throw new Exception(e);
        }
        return path;
    }

The upload method declaration and MessageHandler is as follows

@MessagingGateway(asyncExecutor = "sftpAsync")
    public interface UploadGateway {
        @Gateway(requestChannel = "toSftpChannel")
        void upload(@Payload byte[] file, @Header("filename") String filename, @Header("path") String path);
    }

 @Bean
    @ServiceActivator(inputChannel = "toSftpChannel")
    public MessageHandler handler() {
        SftpMessageHandler handler = new SftpMessageHandler(sftpSessionFactory());
        ExpressionParser expressionParser = new SpelExpressionParser();
        handler.setRemoteDirectoryExpression(expressionParser.parseExpression("headers['path']"));
        handler.setFileNameGenerator(msg -> (String) msg.getHeaders().get("filename"));
        handler.setAutoCreateDirectory(true);
        return handler;
    }

It works fine for uploading files to a remote SFTP server. But after couple of execution, it starts showing

java.lang.OutOfMemoryError: Direct buffer memory
    at java.nio.Bits.reserveMemory(Unknown Source)
    at java.nio.DirectByteBuffer.<init>(Unknown Source)
    at java.nio.ByteBuffer.allocateDirect(Unknown Source)
    at sun.nio.ch.Util.getTemporaryDirectBuffer(Unknown Source)
    at sun.nio.ch.IOUtil.read(Unknown Source)
    at sun.nio.ch.FileChannelImpl.read(Unknown Source)
    at sun.nio.ch.ChannelInputStream.read(Unknown Source)
    at sun.nio.ch.ChannelInputStream.read(Unknown Source)
    at sun.nio.ch.ChannelInputStream.read(Unknown Source)
    at java.nio.file.Files.read(Unknown Source)
    at java.nio.file.Files.readAllBytes(Unknown Source)

payload = Files.readAllBytes(Paths.get(files[i].toURI())); is the line where it throws the above error message.

As per my understanding, I am reading entire file into byte array, hence I am getting this error. Since I need entire file to send to upload method ,I have followed byte[] approach.

I already checked below mentioned threads.

Byte[] and java.lang.OutOfMemoryError reading file by bits

java.lang.OutOfMemoryError: Direct buffer memory when invoking Files.readAllBytes

but the upload method need entire file instead of stream of bytes or chunks of data (correct me if i am wrong).

So,any suggestions to avoid above issue is great help.

Thanks.