Hide input on command line

Question

I know that command line interfaces like Git and others are able to hide input from a user (useful for passwords). Is there a way to programmtically do this in Java? I'm taking password input from a user and I would like their input to be "hidden" on that particular line (but not on all of them). Here's my code for it (though I doubt it would be helpful...)

try (Scanner input = new Scanner(System.in)) {
  //I'm guessing it'd probably be some property you set on the scanner or System.in right here...
  System.out.print("Please input the password for " + name + ": ");
  password = input.nextLine();
}

Answer 1

Try java.io.Console.readPassword. You'll have to be running at least Java 6 though.

   /**
    * Reads a password or passphrase from the console with echoing disabled
    *
    * @throws IOError
    *         If an I/O error occurs.
    *
    * @return  A character array containing the password or passphrase read
    *          from the console, not including any line-termination characters,
    *          or <tt>null</tt> if an end of stream has been reached.
    */
    public char[] readPassword() {
        return readPassword("");
    }

Beware though, this doesn't work with the Eclipse console. You'll have to run the program from a true console/shell/terminal/prompt to be able to test it.

Answer 2

Yes can be done. This is called Command-Line Input Masking. You can implement this easily.

You can uses a separate thread to erase the echoed characters as they are being entered, and replaces them with asterisks. This is done using the EraserThread class shown below

import java.io.*;

class EraserThread implements Runnable {
   private boolean stop;

   /**
    *@param The prompt displayed to the user
    */
   public EraserThread(String prompt) {
       System.out.print(prompt);
   }

   /**
    * Begin masking...display asterisks (*)
    */
   public void run () {
      stop = true;
      while (stop) {
         System.out.print("\010*");
     try {
        Thread.currentThread().sleep(1);
         } catch(InterruptedException ie) {
            ie.printStackTrace();
         }
      }
   }

   /**
    * Instruct the thread to stop masking
    */
   public void stopMasking() {
      this.stop = false;
   }
}

With using this thread

public class PasswordField {

   /**
    *@param prompt The prompt to display to the user
    *@return The password as entered by the user
    */
   public static String readPassword (String prompt) {
      EraserThread et = new EraserThread(prompt);
      Thread mask = new Thread(et);
      mask.start();

      BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
      String password = "";

      try {
         password = in.readLine();
      } catch (IOException ioe) {
        ioe.printStackTrace();
      }
      // stop masking
      et.stopMasking();
      // return the password entered by the user
      return password;
   }
}

This Link discuss in details.

Answer 3

JLine 2 may be of interest. As well as character masking, it'll provide command-line completion, editing and history facilities. Consequently it's very useful for a CLI-based Java tool.

To mask your input:

String password = new jline.ConsoleReader().readLine(new Character('*'));

Answer 4

There is :

Console cons;
char[] passwd;
if ((cons = System.console()) != null &&
    (passwd = cons.readPassword("[%s]", "Password:")) != null) {
    ...
    java.util.Arrays.fill(passwd, ' ');
}

source

but I don't think this works with an IDE like Eclipse because the program is run as a background process rather than a top level process with a console window.

Another approach is to use the JPasswordField in swing with the accompanying actionPerformed method:

public void actionPerformed(ActionEvent e) {
    ...
    char [] p = pwdField.getPassword();
}

source

Answer 5

Here is an example using console.readPassword(...); in an IDE. I use Netbeans. Note: In your IDE, Scanner will be used and it will show the password!. In the console, console.readPassword(..) will be used and it will not show the password!.

 public static void main(String[] args) {
     //The jar needs to be run from the terminal for console to work.
     Scanner input = new Scanner(System.in);

     Console console = System.console();
     String username = "";
     String password = "";
     if (console == null) 
     {
         System.out.print("Enter username: ");
         username = input.nextLine();
         System.out.print("Enter password: ");
         password = input.nextLine();
     }
     else 
     {
         username = console.readLine("Enter username: ");
         password = new String(console.readPassword("Enter password: "));
     }
     
     //I use the scanner for all other input in the code!
     //I do not know if there are any pitfalls associated with using the Scanner and console in this manner!
  }      

Note: I do not know if there are any pitfalls associated with using the Scanner and console in this manner!

Answer 6

The class Console has a method readPassword() that might solve your problem.