Java: Generate random alpha numeric string

Below snippet returns random string of fixed length.

public static String randomString(int len) {

         final StringBuilder builder = new StringBuilder(len);

         for (int i = 0; i < len; i++)

                  builder.append(ALPHA_NUMERICALS.charAt(rnd.nextInt(LENGTH)));

                 

         return builder.toString();

}

App.java

package com.sample.app;

import java.io.UnsupportedEncodingException;
import java.security.SecureRandom;

public class App {

 private static final String ALPHA_NUMERICALS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 private static SecureRandom rnd = new SecureRandom();
 private static final int LENGTH = ALPHA_NUMERICALS.length();

 public static String randomString(int len) {
  final StringBuilder builder = new StringBuilder(len);

  for (int i = 0; i < len; i++)
   builder.append(ALPHA_NUMERICALS.charAt(rnd.nextInt(LENGTH)));

  return builder.toString();
 }

 public static void main(String args[]) throws UnsupportedEncodingException {
  System.out.println(randomString(10));
 }

}

Sample Output

aKXQq3BNlG

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