Is there a way in Java to determine if a path is valid without attempting to create a file?
I need to determine if a user-supplied string is a valid file path (i.e., if createNewFile()
will succeed or throw an Exception) but I don't want to bloat the file system with useless files, created just for validation purposes.
Is there a way to determine if the string I have is a valid file path without attempting to create the file?
I know the definition of "valid file path" varies depending on the OS, but I was wondering if there was any quick way of accepting C:/foo
or /foo
and rejecting banana
.
A possible approach may be attempting to create the file and eventually deleting it if the creation succeeded, but I hope there is a more elegant way of achieving the same result.
Path class introduced in Java 7 adds new alternatives, like the following:
/**
* <pre>
* Checks if a string is a valid path.
* Null safe.
*
* Calling examples:
* isValidPath("c:/test"); //returns true
* isValidPath("c:/te:t"); //returns false
* isValidPath("c:/te?t"); //returns false
* isValidPath("c/te*t"); //returns false
* isValidPath("good.txt"); //returns true
* isValidPath("not|good.txt"); //returns false
* isValidPath("not:good.txt"); //returns false
* </pre>
*/
public static boolean isValidPath(String path) {
try {
Paths.get(path);
} catch (InvalidPathException | NullPointerException ex) {
return false;
}
return true;
}
Edit:
Note Ferrybig's
comment : "The only disallowed character in a file name on Linux is the NUL character, this does work under Linux."
This would check for the existance of the directory as well.
File file = new File("c:\\cygwin\\cygwin.bat");
if (!file.isDirectory())
file = file.getParentFile();
if (file.exists()){
...
}
It seems like file.canWrite() does not give you a clear indication if you have permissions to write to the directory.
File.getCanonicalPath()
is quite useful for this purpose. IO exceptions are thrown for certain types of invalid filenames (e.g. CON
, PRN
, *?*
in Windows) when resolving against the OS or file system. However, this only serves as a preliminary check; you will still need to handle other failures when actually creating the file (e.g. insufficient permissions, lack of drive space, security restrictions).