Reading a remote file using Java

Question

I am looking for an easy way to get files that are situated on a remote server. For this I created a local ftp server on my Windows XP, and now I am trying to give my test applet the following address:

try
{
    uri = new URI("ftp://localhost/myTest/test.mid");
    File midiFile = new File(uri);
}
catch (Exception ex)
{
}

and of course I receive the following error:

URI scheme is not "file"

I've been trying some other ways to get the file, they don't seem to work. How should I do it? (I am also keen to perform an HTTP request)

Dexterdexterity

Answer 1

You can't do this out of the box with ftp.

If your file is on http, you could do something similar to:

URL url = new URL("http://q.com/test.mid");
InputStream is = url.openStream();
// Read from is

If you want to use a library for doing FTP, you should check out Apache Commons Net

Ebonee

Any suggestions if I want files created in last 24 hours to be copied from remote server to local? – Antevert

Answer 2

Reading binary file through http and saving it into local file (taken from here):

URL u = new URL("http://www.java2s.com/binary.dat");
URLConnection uc = u.openConnection();
String contentType = uc.getContentType();
int contentLength = uc.getContentLength();
if (contentType.startsWith("text/") || contentLength == -1) {
  throw new IOException("This is not a binary file.");
}
InputStream raw = uc.getInputStream();
InputStream in = new BufferedInputStream(raw);
byte[] data = new byte[contentLength];
int bytesRead = 0;
int offset = 0;
while (offset < contentLength) {
  bytesRead = in.read(data, offset, data.length - offset);
  if (bytesRead == -1)
    break;
  offset += bytesRead;
}
in.close();

if (offset != contentLength) {
  throw new IOException("Only read " + offset + " bytes; Expected " + contentLength + " bytes");
}

String filename = u.getFile().substring(filename.lastIndexOf('/') + 1);
FileOutputStream out = new FileOutputStream(filename);
out.write(data);
out.flush();
out.close();

Barquisimeto

Answer 3

You are almost there. You need to use URL, instead of URI. Java comes with default URL handler for FTP. For example, you can read the remote file into byte array like this,

    try {
        URL url = new URL("ftp://localhost/myTest/test.mid");
        InputStream is = url.openStream();
        ByteArrayOutputStream os = new ByteArrayOutputStream();         
        byte[] buf = new byte[4096];
        int n;          
        while ((n = is.read(buf)) >= 0) 
            os.write(buf, 0, n);
        os.close();
        is.close();         
        byte[] data = os.toByteArray();
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

However, FTP may not be the best protocol to use in an applet. Besides the security restrictions, you will have to deal with connectivity issues since FTP requires multiple ports. Use HTTP if all possible as suggested by others.

Otterburn

Answer 4

I find this very useful: https://docs.oracle.com/javase/tutorial/networking/urls/readingURL.html

import java.net.*;
import java.io.*;

public class URLReader {
    public static void main(String[] args) throws Exception {

        URL oracle = new URL("http://www.oracle.com/");
        BufferedReader in = new BufferedReader(
            new InputStreamReader(oracle.openStream()));

        String inputLine;
        while ((inputLine = in.readLine()) != null)
            System.out.println(inputLine);
        in.close();
    }
}

Soho

Answer 5

This worked for me, while trying to bring the file from a remote machine onto my machine.

NOTE - These are the parameters passed to the function mentioned in the code below:

String domain = "xyz.company.com";
String userName = "GDD";
String password = "fjsdfks";

(here you have to give your machine ip address of the remote system, then the path of the text file (testFileUpload.txt) on the remote machine, here C$ means C drive of the remote system. Also the ip address starts with \\ , but in order to escape the two backslashes we start it \\\\ )

String remoteFilePathTransfer = "\\\\13.3.2.33\\c$\\FileUploadVerify\\testFileUpload.txt";

(here this is the path on the local machine at which the file has to be transferred, it will create this new text file - testFileUploadTransferred.txt, with the contents on the remote file - testFileUpload.txt which is on the remote system)

String fileTransferDestinationTransfer = "D:/FileUploadVerification/TransferredFromRemote/testFileUploadTransferred.txt";

import java.io.File;
import java.io.IOException;

import org.apache.commons.vfs.FileObject;
import org.apache.commons.vfs.FileSystemException;
import org.apache.commons.vfs.FileSystemManager;
import org.apache.commons.vfs.FileSystemOptions;
import org.apache.commons.vfs.Selectors;
import org.apache.commons.vfs.UserAuthenticator;
import org.apache.commons.vfs.VFS;
import org.apache.commons.vfs.auth.StaticUserAuthenticator;
import org.apache.commons.vfs.impl.DefaultFileSystemConfigBuilder;

public class FileTransferUtility {

    public void transferFileFromRemote(String domain, String userName, String password, String remoteFileLocation,
            String fileDestinationLocation) {

        File f = new File(fileDestinationLocation);
        FileObject destn;
        try {
            FileSystemManager fm = VFS.getManager();

            destn = VFS.getManager().resolveFile(f.getAbsolutePath());

            if(!f.exists())
            {
                System.out.println("File : "+fileDestinationLocation +" does not exist. transferring file from : "+ remoteFileLocation+" to: "+fileDestinationLocation);
            }
            else
                System.out.println("File : "+fileDestinationLocation +" exists. Transferring(override) file from : "+ remoteFileLocation+" to: "+fileDestinationLocation);

            UserAuthenticator auth = new StaticUserAuthenticator(domain, userName, password);
            FileSystemOptions opts = new FileSystemOptions();
            DefaultFileSystemConfigBuilder.getInstance().setUserAuthenticator(opts, auth);
            FileObject fo = VFS.getManager().resolveFile(remoteFileLocation, opts);
            System.out.println(fo.exists());
            destn.copyFrom(fo, Selectors.SELECT_SELF);
            destn.close();
            if(f.exists())
            {
                System.out.println("File transfer from : "+ remoteFileLocation+" to: "+fileDestinationLocation+" is successful");
            }
        }

        catch (FileSystemException e) {
            e.printStackTrace();
        }

    }

}

Autostrada

Answer 6

I have coded a Java Remote File client/server objects to access a remote filesystem as if it was local. It works without any authentication (which was the point at that time) but it could be modified to use SSLSocket instead of standard sockets for authentication.

It is very raw access: no username/password, no "home"/chroot directory.

Everything is kept as simple as possible:

Server setup

JRFServer srv = JRFServer.get(new InetSocketAddress(2205));
srv.start();

Client setup

JRFClient cli = new JRFClient(new InetSocketAddress("jrfserver-hostname", 2205));

You have access to remote File, InputStream and OutputStream through the client. It extends java.io.File for seamless use in API using File to access its metadata (i.e. length(), lastModified(), ...).

It also uses optional compression for file chunk transfer and programmable MTU, with optimized whole-file retrieval. A CLI is built-in with an FTP-like syntax for end-users.

Herbherbaceous

Answer 7

org.apache.commons.io.FileUtils.copyURLToFile(new URL(REMOTE_URL), new File(FILE_NAME), CONNECT_TIMEOUT, READ_TIMEOUT);

Penitentiary

Answer 8

Since you are on Windows, you can set up a network share and access it that way.

Numidia