Say you are given a
java.io.File object that was made like so:
File f = new File("/foo/./././goo");
Say that you need a File object for the parent dir -- which is "/foo"
in this case.
If you do this:
File parent = f.getAbsoluteFile().getParentFile()
parent will be
"/foo/././"
File grandparent = parent.getParentFile()
grandparent will be
"/foo/."
I.e. getParent and getParentFile are pretty dumb. They just strip off
the last path seperator without looking at it.
Now if you do the following with the original file, you get the "real"
parent dir. This is the trick.
File parent = new File(f, "..");
parent --> "/foo"
------------------------------
I.e. never call getParent or getParentFile -- it will not work with
relative path portions.
instead use the File constructor with ".." as the filename.
-------------------------------
Another possible solution is to sanitize the original File with
getCanonicalFile() to get rid of the relative path portions.
this has 3 problems -
1) Your path will have error-prone and unneccessary (usually)
backslashes in Windows
2) It's more work and requires a try/catch block
3) It handles symbolic link files differently
The reason I'm sending this tip out is that I got burned by this
behavior. I had code that was getting a crucial parent directory. It
was working fine for months. Then in code a hundred levels above it, a
"." was inserted just before the final directory name.
KABOOM.
Ref:
http://bt2ws.central.sun.com/CrPrint?id=6687287
--
Byron Nevins Work 408-276-4089, Home 650-359-1290, Cell 650-784-4123 - Sun Microsystems, Inc.