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file.renameTo : linux v windows

Posted on 2004-08-01
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Last Modified: 2008-01-09
Can someone tell me why this works on Windows but not on Linux if renaming to a different partition :

import java.io.*;

public class moveFile {

public static void main(String[] args) {
File f = new File(args[0]);
System.out.println("Moving file "+args[0]+" to "+args[1]);
boolean ok = f.renameTo(new File(args[1]));
System.out.println("Move file was : "+ok);

}
}

running it on Linux with :

this works : java moveFile /opt/test1/testfile /opt/test2/testfile
this doesn't : java moveFile /opt/testfile /tmp/testfile

Thanks,

D.
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Question by:damianharvey
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9 Comments
 
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Expert Comment

by:objects
ID: 11690193
because renaming to a different partition is actually a copy and delete if across partitions.
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Author Comment

by:damianharvey
ID: 11690559
So what stops this working? It isn't a permissions thing. I've chmod'ed all the dirs and files and run it as root.

What do most people do to get this functionality on Linux?
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Expert Comment

by:objects
ID: 11690569
I don't think you can avoid doing a copy/delete.
what happens if you do a mv from command line?
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Author Comment

by:damianharvey
ID: 11690676
mv from command prompt is fine. No issues.

It is specific only to java. I can move files using the Linux Tools (eg. Konqueror) with no issues as well.

Just found a couple of links on google that suggest that it isn't possible for Java to rename across Partitions/Devices. Seems odd that such functionality would be crippled on Linux.
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Expert Comment

by:objects
ID: 11690721
from the javadoc:

"Whether or not this method can move a file from one filesystem to another is platform-dependent"
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Expert Comment

by:sciuriware
ID: 11691019
Since Windows 2000 the C-API supports renaming to be a move file.
So JAVA on Windows just tries an ordinary rename which is (sometimes!) carried out as a file move
on the OS-level. LINUX and UNIX don't.
The implementation of the rename operation is the cause of all this and not visible
from JAVA. The best you can do is write code that "copies & deletes" when a rename fails.
So I did.
;JOOP!
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Accepted Solution

by:
objects earned 125 total points
ID: 11692003
A workaround would be to use Runtime.exec() to call mv
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Author Comment

by:damianharvey
ID: 11722976
mv is the way to go I think. Here's the code I ended up using. I'm not sure why but the "-c" is required to get it working :

            if(!file.renameTo(archiveFile)) {
                        //Rename was not sucessful
                        if(File.separator.equals("/")) {
                              //You're on UNIX-LINUX-Solaris etc
                              try {
                                    
                                    String[] cmd = {"/bin/bash", "-c", "mv "+replaceSpaces(file.getAbsolutePath())+" "+replaceSpaces(archiveFile.getAbsolutePath())};
                                    log("Rename didn't work. Executing 'mv' command - "+cmd[0]+"; "+cmd[1]+"; "+cmd[2]);
                                    Process p = Runtime.getRuntime().exec(cmd);
                                    BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
                                    BufferedReader stdErr = new BufferedReader(new InputStreamReader(p.getErrorStream()));

                                    String content = "";
                                    
                                    while((content = stdInput.readLine()) != null) {
                                          log("Command std output : "+content);
                                    }
                                    stdInput.close();
                                    
                                    while((content = stdErr.readLine()) != null) {
                                          log("Command err output : "+content);
                                    }
                                    stdErr.close();
                                                                  
                                    log("Moved the file successfully using mv");
                                    
                                    return true;
                                    
                              } catch(IOException e) {
                                    log("IOException using mv on *IX System :"+e);
                              }
                        }
            } else {
                log("Moved the file successfully using rename");
                return true;
            }
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Expert Comment

by:sciuriware
ID: 11723443
I found that it's faster (!?) and more controllable to copy a file yourself (don't ask me why/how).
So, I made a 'move' in JAVA because of system-independency:

     if(fileOld.renameTo(fileNew))
     {
            if(copy(fileOld, fileNew)) // true == OK
            {
                     fileOld.delete();
            }
     }

You can easily make your own copy show progress on the screen and copy filemode as well.
;JOOP!
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