Java Spring Boot FTPClient connection method from another class doesn´t work

Question

I am trying to make a extra class that would take care of connection and status of the user, but I am still getting some wierd error, that I don´t understand.

This is my ´FTPConnection class I created private ftpClient using DI (I have @Bean annotation in main class) and I am trying to connect to the server using this method from another class

@Autowired
private FTPClient ftpClient;

public void connect() {
    try {
        ftpClient.connect("host");
        ftpClient.login("username", "password");

        int reply = ftpClient.getReplyCode();

        if (!FTPReply.isPositiveCompletion(reply)) {
            ftpClient.disconnect();
            System.err.println("FTP server refused connection.");
            System.exit(1);
        }

    }
    catch (IOException ex) {
        System.out.println(ex.getMessage());
    }
}

And this is the class with the RequestMapping methods

@PostMapping("/uploadFile")
    public void uploadFile(@RequestParam("file") MultipartFile file) {

        var connection = new FTPConnection();

        try {

            connection.connect();
            System.out.println(connection.isConnected());
            FTPClient ftpClient = connection.getFtpClient();

            ftpClient.changeWorkingDirectory("/usb");
            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

            [...]

And the error that I am getting is

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root java.lang.NullPointerException: null at com.tenpetr.FTPFileUploader.FTPConnection.connect(FTPConnection.java:16) ~[main/:na] at com.tenpetr.FTPFileUploader.FileTransfer.uploadFile(FileTransfer.java:29) ~[main/:na] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)...

Dou you have any idea, why I am stuck here? Thanks for your advices.

Answer 1

My guess is (will update after having more data) that the FtpClient is not correctly initialized and thus the FtpConnection is not correctly initialized as well.

TO BE UPDATED

Answer 2

Defining a bean with singleton scope means the container creates a single instance of that bean

edited:

@Bean
@Scope("singleton")
    public FTPClient  ftpClient(){
        return new FTPClient();
    }

This won't work if you're trying to autowire an interface