Java 1.6 - determine symbolic links

Question

In a DirectoryWalker class I want to find out if a File instance is actually a symbolic link to a directory (assuming, the walker walks on UNIX systems). Given, I already know the instance is a directory, would the following be a reliable condition to determine the symbolic link?

File file; // ...       if (file.getAbsolutePath().equals(file.getCanonicalPath())) {     // real directory ---> do normal stuff       } else {     // possible symbolic link ---> do link stuff } 

Answer 1

The technique used in Apache Commons uses the canonical path to the parent directory, not the file itself. I don't think that you can guarantee that a mismatch is due to a symbolic link, but it's a good indication that the file needs special treatment.

This is Apache code (subject to their license), modified for compactness.

public static boolean isSymlink(File file) throws IOException {   if (file == null)     throw new NullPointerException("File must not be null");   File canon;   if (file.getParent() == null) {     canon = file;   } else {     File canonDir = file.getParentFile().getCanonicalFile();     canon = new File(canonDir, file.getName());   }   return !canon.getCanonicalFile().equals(canon.getAbsoluteFile()); } 

Answer 2

Java 1.6 does not provide such low level access to the file system. Looks like NIO 2, which should be included in Java 1.7, will have support for symbolic links. A draft of the new API is available. Symbolic links are mentioned there, creating and following them is possible. I'm not exactly sure that which method should be used to find out whether a file is a symbolic link. There's a mailing list for discussing NIO 2 - maybe they will know.