Java FTP Delete?

[jmace]

Well, I've been learning Java and I managed to create an FTP client that uploads and downloads files from a server. Oddly, the thing I can't figure out is how to do an FTP delete. Can anyone help me on that? I don't want to use an API or someone else's class. (How would I learn from that? ;)

I've tried looking through some existing API's for hints, but their too complicated for me to figure out. You have to go from function to function in tons of files and I still don't get it.

Any help or suggestions would be great! Thanks everyone.

[DavidKroukamp]

Well, I've been learning Java and I managed to create an FTP client that uploads and downloads files from a server. Oddly, the thing I can't figure out is how to do an FTP delete. Can anyone help me on that? I don't want to use an API or someone else's class. (How would I learn from that? ;)

I've tried looking through some existing API's for hints, but their too complicated for me to figure out. You have to go from function to function in tons of files and I still don't get it.

Any help or suggestions would be great! Thanks everyone.

might this help:

package org.kodejava.example.commons.net;

import org.apache.commons.net.ftp.FTPClient;
import java.io.IOException;

public class FtpDeleteDemo {

    public static void main(String[] args) {
        FTPClient client = new FTPClient();
        try {
            client.connect("ftp.domain.com");
            client.login("admin", "secret");
// Delete file on the FTP server. When the FTP delete complete 
// it returns true.
            String filename = "/testing/data.txt";
            boolean deleted = client.deleteFile(filename);
            if (deleted) {
                System.out.println("File deleted...");
            }
            client.logout();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

[jmace]

Thanks for the quick reply. That code uses the ftpClient API, which I'm trying to avoid. :( Is there an example that doesn't use an API?

[NormR1]

Have you read the RFC on how FTP works?
You can use a Socket connection to send the FTP server commands made of Strings.
You need to know the protocol for it to work.

[jmace]

How would I go about that? I've never understood sockets. I mean, I understand the concept, but I've never successfully used them. I guess what I am asking is, where is a good place to go to understand sockets and how they relate to my current dilemma?

[NormR1]

Here's a link to the tutorial about Sockets:
http://docs.oracle.com/javase/tutorial/networking/sockets/index.html

How did you think you could communicate with a server? I assume you want to write client code to talk to a FTP server over the internet and ask it to do things for you.

[jmace]

Thanks for the link. Thus far in my code I've used things like:

//conn is a URLConnection. A socket of sorts, I suppose...

	OutputStream os = conn.getOutputStream();
  	BufferedOutputStream bos = new BufferedOutputStream(os);

  	byte[] buffer = new byte[1024];
  	int r;

  	while((r = bis.read(buffer)) > 0){
  		//write the file
  	}

which I've never really thought of as sockets.

[NormR1]

That could work. Try it and see how it goes.

[jmace]

Haha. I feel foolish now. That tutorial is essentially what I am doing. I guess when I think of Sockets I think of the C++ methods that are infinitely more complex.

At any rate, how can I use that to delete a file? I understand how to transfer a file with it, but somewhere in my disconnected brain I can't figure out how use it to remove a file.

EDIT: cross post. The above does work for uploading. As I said, I can upload and download, I just can't delete files.

[NormR1]

With FTP you send a request to the server. The server does what you ask.
You need to read the doc on the protocol. One place is the RFC doc for FTP.

[jmace]

So, I looked through http://www.w3.org/Protocols/rfc959/8_PortNumber.html and some other specs on W3C, but I still don't understand. Forgive my slow-ness. I know the command that I need to send to the server is

DELE <SP> <pathname> <CRLF>

but I don't know how to send it with Java. Do you?

[NormR1]

Connect to the server and send the command as a String.

I don't know if this will be helpful or confusing. I wrote an FTP Server a few years ago.
Here is its console log from when I connect to it with a FTP tool: WS_FTP95.

FTPrun(): connected accepted Socket[addr=/127.0.0.1,port=4145,localport=21]
ServerSocket[addr=0.0.0.0/0.0.0.0,port=0,localport=21]
MyIP4PASV: 127,0,0,1,
writeString: writing >220 Norms FTP server ready.
< (end of writing) <<<
FTPreq: >USER Norm<
writeString: writing >331 Password required.
< (end of writing) <<<
FTP req: PASS asdf
writeString: writing >230 User logged in.
< (end of writing) <<<
FTP request: PWD
writeString: writing >257 "D:/www/" is current directory.
< (end of writing) <<<
FTP request: SYST
writeString: writing >215 NAME Norm's FTP Server
< (end of writing) <<<
FTP request: HELP
writeString: writing >214-The following commands are recognized:
USER
QUIT
ABOR
TYPE
LIST
PWD
MKD
CWD
TYPE
PORT
SYST
HELP
NLST
CDUP
PASV
RETR
STOR
214 Help command successful.
< (end of writing) <<<
FTP request: PORT 127,0,0,1,16,50
dpH RmtAddr: 127.0.0.1:4146
dpH OSocket: Socket[addr=/127.0.0.1,port=4146,localport=20]
writeString: writing >220 PORT Command successful.
< (end of writing) <<<
FTP request: LIST
writeString: writing >150 Opening ASCII mode data connection.
< (end of writing) <<<
dpHdoLIST: >< true
writeString: writing >226 Transfer complete.
< (end of writing) <<<
FTP request: PWD
writeString: writing >257 "D:/www/" is current directory.
< (end of writing) <<<
FTP request: PORT 127,0,0,1,16,51
dpH RmtAddr: 127.0.0.1:4147
dpH OSocket: Socket[addr=/127.0.0.1,port=4147,localport=20]
writeString: writing >220 PORT Command successful.
< (end of writing) <<<
FTP request: LIST
writeString: writing >150 Opening ASCII mode data connection.
< (end of writing) <<<
dpHdoLIST: >< true
writeString: writing >226 Transfer complete.
< (end of writing) <<<
FTP request: QUIT
User: Norm logged off
writeString: writing >221 Goodbye.
< (end of writing) <<<
FTPrun(): waiting on connect at Mon Jan 23 21:07:52 EST 2012 ServerSocket[addr=0.0.0.0/0.0.0.0,port=0,localport=21]

The Strings inside of the > < are what the server received or sent.
The one in red was received from the client.
The one in green was what was sent to the client

[jmace]

Thank you for sticking with me on this. The concept of what needs to be done is relatively clear (ish), but the application is completely absent. I haven't the slightest idea how to send that String command to the FTP server. I know sockets will need to be involved, but I don't understand the specifics. Essentially, this is the conundrum that I've been stuck on for the past week or so.

Suppose I do a URLConnection again to connect to the server, where specifically would the string go and how would I get it there? I imagine that I wouldn't still be using a BufferedOutputStream. And I have my doubts that the URLConnection would even be appropriate-- to which URL would I connect? If it's to the file I want deleted, wouldn't it the write the command to the file rather than execute it? I'm so confused. Any application help would be fantastic.

[NormR1]

See my last post. It has part of a dialog between a FTP server and a client.
The client was an FTP tool I got years ago. I suspect it uses sockets.

[jmace]

Sorry, I missed that edit. From what you posted, it looks like I should set up a connections to the top-level domain, or perhaps even the IP Address (though I don't suppose it would really make a difference either way). Now I have to figure out how to send FTP commands. . . .

[NormR1]

how to send FTP commands.

Use the output stream you get from a Socket.

[jmace]

Like this?

try{
			URL url = new URL("ftp://"+this.user+":"+this.password+"@"+this.url);
			URLConnection conn = url.openConnection();

			OutputStream os = conn.getOutputStream();
		  	BufferedOutputStream bos = new BufferedOutputStream(os);

		  	String cmd = "DELE "+file+"\n";

		  	bos.write(cmd.getBytes());
		  	
		  	bos.close();
	      
		  	return "\n     File Deleted!";
		}catch(Exception ex){
			return "\n     File Failed to delete!";
		}

I don't think it will work....

EDIT:

java.io.IOException: illegal filename for a PUT
at sun.net.www.protocol.ftp.FtpURLConnection.getOutputStream(Unknown Source)
at ftpClient.ftpdel(ftpClient.java:155)
at console.ftpDel(console.java:676)
at console.localCommand(console.java:436)
at console.proccessCommand(console.java:347)
at console.runCommand(console.java:263)
at console$3.keyTyped(console.java:114)
at java.awt.Component.processKeyEvent(Unknown Source)
at javax.swing.JComponent.processKeyEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

[NormR1]

How does the short piece of code relate to the stack trace?
For example: Where is line 155

What is the value of the variable: url?

[jmace]

OH MY GOSH!

try{
			Socket socket = new Socket (this.url, 21);
			PrintStream out = null;
			out = new PrintStream (socket.getOutputStream());
			out.println("user "+ this.user + "\n");
			out.println("pass "+ this.password + "\n");
			out.println("DELE "+ file + "\n");
			out.close();
			return "Okay!";
		}catch(Exception e){
			e.printStackTrace();
			return "Fail!";
		}

THAT'S IT! IT WORKS! My FTP Client is FINIHSED!!!

Thanks for your insights, my friend.

[NormR1]

Congratulations on getting your code to work.

I wouldn't say it was finished, but at least you have the basics done.