How to check whether a file is on a network share with Java

DangerousPathChecker.java

/** Copyleft (C) 2016 by Aaron Digulla. Use as you wish. This copyright notice can be removed. */

package bug507401;

import java.io.BufferedReader;
import java.io.File;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.List;

/**
 * Check whether a file is on a network drive.
 * 
 * <p>Based on ideas from 
 * <a href="https://sites.google.com/site/baohuagu/how-to-detect-if-a-drive-is-network-drive">How to detect if a drive is network drive?</a>
 * and <a href="http://stackoverflow.com/questions/9163707/java-how-to-determine-the-type-of-drive-a-file-is-located-on">Java: how to determine the type of drive a file is located on?</a>
 */
public class DangerousPathChecker {

    private final static boolean IS_WINDOWS = isWindows();

    // Along the lines of org.apache.commons.lang3.SystemUtils.IS_OS_WINDOWS
    private static boolean isWindows() {
        String os = System.getProperty("os.name").toLowerCase();
        return os.startsWith("Windows");
    }
    
    public boolean isDangerous(File file) {
        if (!IS_WINDOWS) {
            return false;
        }
        
        // Make sure the file is absolute
        file = file.getAbsoluteFile();
        String path = file.getPath();
//        System.out.println("Checking [" + path + "]");
        
        // UNC paths are dangerous
        if (path.startsWith("//")
            || path.startsWith("\\\\")) {
            // We might want to check for \\localhost or \\127.0.0.1 which would be OK, too
            return true;
        }
        
        String driveLetter = path.substring(0, 1);
        String colon = path.substring(1, 2);
        if (!":".equals(colon)) {
            throw new IllegalArgumentException("Expected 'X:': " + path);
        }
        
        return isNetworkDrive(driveLetter);
    }

    /** Use the command <code>net</code> to determine what this drive is.
     * <code>net use</code> will return an error for anything which isn't a share.
     * 
     *  <p>Another option would be <code>fsinfo</code> but my gut feeling is that
     *  <code>net</code> should be available and on the path on every installation
     *  of Windows.
     */
    private boolean isNetworkDrive(String driveLetter) {
        List<String> cmd = Arrays.asList("cmd", "/c", "net", "use", driveLetter + ":");
        
        try {
            Process p = new ProcessBuilder(cmd)
                .redirectErrorStream(true)
                .start();
        
            p.getOutputStream().close();
            
            StringBuilder consoleOutput = new StringBuilder();
            
            String line;
            try (BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
                while ((line = in.readLine()) != null) {
                    consoleOutput.append(line).append("\r\n");
                }
            }
            
            int rc = p.waitFor();
//            System.out.println(consoleOutput);
//            System.out.println("rc=" + rc);
            return rc == 0;
        } catch(Exception e) {
            throw new IllegalStateException("Unable to run 'net use' on " + driveLetter, e);
        }
    }
    
    public static void main(String[] args) {
        DangerousPathChecker checker = new DangerousPathChecker();
        
        checker.check("");
        checker.check("//server/path");
        checker.check("\\\\server\\path");
        checker.check("c:");
        checker.check("c:/windows");
        checker.check("c:\\windows");
        // On my computer, Z: is a mapped network drive
        checker.check("z:");
        checker.check("z:/folder");
        checker.check("z:\\folder");
    }

    private void check(String path) {
        File file = new File(path).getAbsoluteFile();
        System.out.println(isDangerous(file) + " - " + file);
    }
}

Thank you for this.
One small bug: the isWindows() method retrieves the os String and converts it to lower case.
Then it checks for "Windows" with an upper case "W". I just changed it to "windows" and it worked like a charm. I also converted the main() method to JUnit tests.
I need to copy a file locally if it is on the network because during a multiple day run that file needs to be accessible pretty much all the time. If a network problem prevents access, even temporarily, the multi-day run is ruined and has to be restarted.