Reading a remote file using Java

Question

Hi all,

I am very new to java, and have been struggling with it. 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. Any insight of how I should do it? This should be straight forward shouldn't it? (BTW, I am also keen to perform an http request)

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

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();

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.

Answer 4

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