Check if file exists using bash inside Java program? - linux

Question

So I am witting a java program for interacting with filesystem.
Java program itself cannot run as super user. I created a special user for this program and gave it some special privileges to run some commands without password (via visudo file).
So I I'd like to check if a file exist. I used:
if(f.exists() && !f.isDirectory()) but the problem is this fails if I am checking if files exist that is read/write protected or if it belongs to another user.
That is why I need to use bash. for example, when I am retrieving information about file I use the following:
String[] command = new String[] { "sudo", "stat", filepath, "-c", "%F##%s##%U##%G##%X##%Y##%Z" };
process = runtime.exec(command); and then just parse the output.
For example moving a file I use this:
String[] command = new String[] {
"sudo",
"-u",
user,
"mv",
source,
target
};
So now I am looking for a way to get simple true/false response when checking if file exist.
I think I could use find command or something similar?

Answer 1

I've solved my issue by using the following command:
String[] command = new String[] { "sudo", "-u", user, "test", "-f", path };
Where user is user who I am running command as. And path is the path-to-file we are testing.
I then read the execute and read command's output in the code below.
I hope it helps someone someday...
process = runtime.exec(command);
errbr = new BufferedReader(new InputStreamReader(process.getErrorStream()));
while ((messageLine = errbr.readLine()) != null) {
message += messageLine + ";";
}
br = new BufferedReader(new InputStreamReader(process.getInputStream()));
while ((messageLine = br.readLine()) != null) {
message += messageLine;
}