How to mask a password when input from the console. Contains a work-around for running within Eclipse; see Eclipse bug #122429.

PasswordMask.java

package org.gkh;

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

public class ConsoleUtil {
	
    /**
     * Handles console input when running outside of Eclipse.
     * 
     * @param cons the console to use in order to receive input
     * @param msg the prompt message
     * @return the password input by the user
     */
    public static String getPasswordMasked(Console cons, String msg)
    {
        char[] passwd;
        while (true) {
            passwd = cons.readPassword("%s", msg);
            if (passwd != null) {
                if (passwd.length > 0) {
                    return new String(passwd);
                } else {
                    System.out.println("Invalid input\n");
                }
            }
        }
    }
    
    /**
     * Handles console input when running inside of Eclipse; See Eclipse bug
     * #122429.
     * 
     * @param msg the prompt message
     * @return the password input by the user
     * @throws IOException if password is zero-length
     */
    public static String getPasswordWithinEclipse(String msg) 
            throws IOException 
    {
        // In Eclipse IDE
        System.out.print(msg);
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                System.in));
        String password = reader.readLine();
        if (password != null) {
            if (password.length() <= 0) {
                System.out.println("Invalid input\n");
                throw new IOException("Error reading in password");
            }
        }
        return password;
    }

	private Util() {}
	
	public static void main(String[] args) {
		String password = null;
		String pwdMessage = "Enter the password: ";
		Console cons = System.console();
		if (cons == null) {
			// We are in the Eclipse IDE.
			try {
				System.out.println("LOG: Running within Eclipse IDE...");
				System.out.println("LOG: Password will not be masked");
				password = Util.getPasswordWithinEclipse(pwdMessage);
				System.out.println("LOG: Password entered");
			} catch (IOException e) {
				System.err.println("Error getting password" + e.getMessage());
				System.exit(1);
			}
		} else {
			password = Util.getPasswordMasked(cons, pwdMessage);
		}
	}
}

@basilroy1 the problem lies with the Eclipse integrated console. System.console() returns null when using it as opposed to an external terminal. The gist is just a hack to get it to run within Eclipse without throwing an NPE. Running in an external terminal does not echo the password.

λ java -cp bin poc.ConsoleUtil
Enter the password:

(prompt returns)

Short of implementing a custom console, you might resort to popping up a Swing dialog when running inside Eclipse, e.g.

    public static String getMaskedPasswordWithinEclipse(String msg) {
    	final String password;
    	final JPasswordField jpf = new JPasswordField();
    	password = JOptionPane.showConfirmDialog(null, jpf, msg,
    			JOptionPane.OK_CANCEL_OPTION,
    			JOptionPane.QUESTION_MESSAGE) == JOptionPane.OK_OPTION ?
    					new String(jpf.getPassword()) : "";
    	return password;
    }

References

1. java.io.Console support in Eclipse IDE
2. System.console() returns null
3. Bug 122429 - System.console() (Java 6.0) returns null when running inside Eclipse