java ftp nullpointer异常

Question

I have code to upload a file to a server.

import org.apache.commons.net.ftp.FTPClient;

    import java.io.File;
    import java.io.IOException;
    import org.apache.commons.net.ftp.FTPFile;
    import java.io.FileInputStream;
    import java.net.SocketException;

    public class FtpConnectDemo {
        public static void main(String[] args) throws SocketException, IOException{
            FTPClient client = new FTPClient();
            FileInputStream fis = null;

            client.connect("ftp.someserver.co.uk",21);
            boolean login = client.login("webmaster@someserver.co.uk",
                    "mypassword");


            String filename = "E:/workbench j2ee/cPEP_UI/WebContent/engine.xml";
            client.storeFile(filename, fis);
            client.logout();
            fis.close();
        }
    }

and when I run this code, it is giving me this error:

Exception in thread "main" java.lang.NullPointerException
    at FtpConnectDemo.main(FtpConnectDemo.java:22)

The username, password, servername are all right. What's wrong then? I am able to connect to FTP using telnet. Any ideas?

EDIT 1

OK, now I am not getting the nullpointer exception, as I initialized fis . But my file is not uploaded yet; what might be the problem?

Answer 1

You never instanciate your variable fis . I think that this is your problem here.

This cause two problems:

• You try to store null as a file, line 20. This is handled by the Apache FTP library you are using.
• NullPointerException line 22, when you try to call close() .

---

Also, other thing I'd like to point out: line 20, when you are calling storeFile . The path you are giving is a path pointing to a local file. I think you should put the remote file path in here.

The final code should look like this:

// ...

FileInputStream fis = new FileInputStream("E:/workbench j2ee/cPEP_UI/WebContent/engine.xml");

// ...

client.storeFile("engine.xml", fis);

// ...

Answer 2

you are missing

fis = new FileInputStream(new File(filename));

before client.storeFile()

Answer 3

看起来您的fis不能是null以外的任何内容（只能使用null初始化它），因此当您尝试对其执行close()时， NullPointerException是自然的。

Answer 4

The sendFile method on client.storeFile returns a boolean. I would first check that value to see if it is failing or maybe just importing to somewhere you're not expecting.

The client also has a getReplyCode and getReplyString methods which you could use to see what the server is up to.