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Java file.canWrite always returning true

This is going to be very short. Actually does not entail a blog post. Anyways, here goes.

So, when I was trying to setup some Junit tests on an EC2 instance, I stumble into this ridiculous failure where, file.canWrite() simply returns true, no matter what. A code like below, keeps printing the "file is writable"

import java.io.File;

public class Test1 {
        public static void main(String[] args) throws Exception {
                File file = new File("hello.txt");
                file.createNewFile();
                file.setReadOnly();
                if (file.canWrite()) {
                        System.out.println("File is writable!");
                } else {
                        System.out.println("File is in read only mode!");
                }
        }
}


Turns out, the culprit is that I am running as "root". Since root can do-it-all, it simply returns true even though the file permissions read


[root@myhost ~]# ls -al hello.txt
-r--r--r--. 1 root root 0 Jan 30 18:52 hello.txt

Kind of subtle, since I would expect the permissions to be the ultimate source of truth.

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