Java check if removable drive in use

Question

I'm working on a Java app and I need to check if a removable drive is in use before ejecting it programatically.

Is it possible to check a drive for open/in-use files in pure Java? As a fallback, is there a shell command that I could call from Java which would do this kind of checking? Ideally, I'd need commands for both Windows and MacOS.

Answer 1

In Java, directly checking if a drive is in use (i.e., if files on the drive are open) is not straightforward due to platform-independent restrictions and security concerns. However, you can use platform-specific methods to achieve this indirectly.

For Windows, you can execute the 'handle' command-line tool using Java's ProcessBuilder to check for open handles on a specific drive. Here's an example:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) {
        try {
            String driveLetter = "E:"; // Replace with the drive letter you want to check
            ProcessBuilder processBuilder = new ProcessBuilder("cmd.exe", "/c", "handle", driveLetter);
            processBuilder.redirectErrorStream(true);
            Process process = processBuilder.start();

            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                // Check for any open handles on the drive
                if (line.contains(driveLetter)) {
                    System.out.println("Drive is in use.");
                    break;
                }
            }

            // Close the reader and wait for the process to finish
            reader.close();
            process.waitFor();
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

For maxOS, you can use the 'lsof' command to list open files. Something like this may work depending on your usecase:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) {
        try {
            String mountPoint = "/Volumes/MyDrive"; // Replace with the mount point of the drive you want to check
            ProcessBuilder processBuilder = new ProcessBuilder("lsof", mountPoint);
            processBuilder.redirectErrorStream(true);
            Process process = processBuilder.start();

            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line;
            boolean inUse = false;
            while ((line = reader.readLine()) != null) {
                // Check if there are any open files on the drive
                if (line.contains(mountPoint)) {
                    inUse = true;
                    break;
                }
            }

            if (inUse) {
                System.out.println("Drive is in use.");
            } else {
                System.out.println("Drive is not in use.");
            }

            // Close the reader and wait for the process to finish
            reader.close();
            process.waitFor();
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}