File.canWrite is not working as per expectations

Question

i am trying to check whether a file is writable or not. i have changed the file permission by myself for all users. but if i try to run the program, it show "true" as a response. if i allow the permissions, then also it is showing "true".

Whats is my problem?

try
  {

     File file = new File("D:/myproject_log/delivery_report_edr.out"); 

        if(!file.canWrite())
        {
            System.out.println("you can't write!!!");
        }
        else
            System.out.println("you can write!!!");
  }
  catch(Exception e)
  {
      e.printStackTrace();
  }

you are doing something wrong in how you think you are setting permissions, your posted code should work as expected if the permissions are set correctly. — , Mar 21 '12 at 14:16
who is the owner of the file and who is running the application? — Woot4Moo, Mar 21 '12 at 14:36
through eclipse i am trying to run the application. i myself created the file, but then took out the permission to write in it. all operations i am doing in my local desktop only. — kunal dexit, Mar 21 '12 at 14:40

score 3 · Answer 1 · answered Jan 02 '14 at 03:22

3

Have you tried using the java.nio.file.Files#isWritable method. as well as File#canWrite ?

answered Jan 02 '14 at 03:22

racc

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I have had same issue with canWrite giving me incorrect answers when I asked if I can create files into the direction. But your answer has fixed the issue ;) – Martin Krajčírovič Aug 16 '18 at 03:23
That's helpful, thanks. `File.canWrite` considers `new File("C:/Windows/System32/");` to be writable, even for non-admin users. `Files#isWritable` actually checks if the current user is allowed to write. – Eric Duminil Nov 15 '22 at 12:59

score 2 · Accepted Answer · answered Mar 21 '12 at 14:16

2

It is working fine. I copied your code and run it twice. First I got You can write, then right click on the file folder, go to properties and select read only and run the program again and I got you can't write

So as per the documentation of the method canWrite() it gave me the expected output. Please confirm your settings once again and check.

answered Mar 21 '12 at 14:16

Chandra Sekhar

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i have changed the permissions to "deny" in windows OS. with the same file i am trying to log my entries. but while creating the logger with the same file, i am getting the exception saying java.io.FileNotFoundException: D:\myproject_log\delivery_report_edr.out (Access is denied) – kunal dexit Mar 21 '12 at 14:29
@user1282551 can you say how you are changing the permission? – Chandra Sekhar Mar 21 '12 at 14:31
in windows, right clicking on the file and then going in properties... there in security tab, i have changed the permission for write by clicking on "deny" option. is it the correct way??? – kunal dexit Mar 21 '12 at 14:34
@user1282551 sorry I can't help you more, but I can say if you change the **General property** of a file to **read-only** then you will get proper outputs. – Chandra Sekhar Mar 21 '12 at 14:51
1

The documentation says: "true if and only if the file system actually contains a file denoted by this abstract pathname and the application is allowed to write to the file; false otherwise". In many situations, canWrite returns true even though the application is _not_ allowed to write to the file, so I wouldn't call this confirming to the documentation at all. The documentation really should be clearer that it won't check permissions to the file at all. – Hakanai Feb 19 '13 at 23:18

score 0 · Answer 3 · edited Oct 02 '12 at 11:12

0

I have also found that File.canWrite() cannot be trusted, especially over network drives, often returning true even though a file write will fail or vice-versa. I made my own method that actually tries to write a dummy file to the dir. That is simple to write and foolproof. Maybe they fixed it though.

edited Oct 02 '12 at 11:12

Marko

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answered Aug 10 '12 at 18:41

Bob

1

score 0 · Answer 4 · answered Jun 04 '14 at 07:43

I had the same issue with a file located in c:\programFiles\folder and the File.canWrite method returned true and i was getting the same exception. when i changed the permission of write as allowed true for USER defined in security tab of Folder properties, It gave me no exception.

File.canWrite is not working as per expectations

4 Answers4