java - How to check if a file is readable?

Question

I'm writing Java 6 application and I have to check if a file is readable. However, on Windows canRead() always returns true. So I see that probably, the only solution could be some native solution based on WINAPI and written in JNA/JNI.

But, there is another problem, because it's difficult to find a simple function in WINAPI which would return information about access to a file. I found GetNamedSecurityInfo or GetSecurityInfo but I'm not an advanced WINAPI programmer and they are too complicated for me in connection with JNA/JNI. Any ideas how to deal with this problem?

Answer 1

Java 7 introduced the Files.isReadable static method, it accepts a file Path and returns true if file exists and is readable, otherwise false.

From the docs

Tests whether a file is readable. This method checks that a file exists and that this Java virtual machine has appropriate privileges that would allow it open the file for reading. Depending on the implementation, this method may require to read file permissions, access control lists, or other file attributes in order to check the effective access to the file. Consequently, this method may not be atomic with respect to other file system operations.

Note that the result of this method is immediately outdated, there is no guarantee that a subsequent attempt to open the file for reading will succeed (or even that it will access the same file). Care should be taken when using this method in security sensitive applications.

Example:

File file = new File("/path/to/file");
Files.isReadable(file.toPath()); // true if `/path/to/file` is readable