Creating a random string with A-Z and 0-9 in Java [duplicate]

Question

Here you can use my method for generating Random String

protected String getSaltString() {
        String SALTCHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
        StringBuilder salt = new StringBuilder();
        Random rnd = new Random();
        while (salt.length() < 18) { // length of the random string.
            int index = (int) (rnd.nextFloat() * SALTCHARS.length());
            salt.append(SALTCHARS.charAt(index));
        }
        String saltStr = salt.toString();
        return saltStr;

    }

The above method from my bag using to generate a salt string for login purpose.

RandomStringUtils from Apache commons-lang might help:

RandomStringUtils.randomAlphanumeric(17).toUpperCase()

---

2017 update: RandomStringUtils has been deprecated, you should now use RandomStringGenerator.

Three steps to implement your function:

Step#1 You can specify a string, including the chars A-Z and 0-9.

Like.

 String candidateChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";

Step#2 Then if you would like to generate a random char from this candidate string. You can use

 candidateChars.charAt(random.nextInt(candidateChars.length()));

Step#3 At last, specify the length of random string to be generated (in your description, it is 17). Writer a for-loop and append the random chars generated in step#2 to StringBuilder object.

Based on this, here is an example public class RandomTest {

public static void main(String[] args) {

    System.out.println(generateRandomChars(
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890", 17));
}

/**
 * 
 * @param candidateChars
 *            the candidate chars
 * @param length
 *            the number of random chars to be generated
 * 
 * @return
 */
public static String generateRandomChars(String candidateChars, int length) {
    StringBuilder sb = new StringBuilder();
    Random random = new Random();
    for (int i = 0; i < length; i++) {
        sb.append(candidateChars.charAt(random.nextInt(candidateChars
                .length())));
    }

    return sb.toString();
}

}

You can easily do that with a for loop,

public static void main(String[] args) {
  String aToZ="ABCD.....1234"; // 36 letter.
  String randomStr=generateRandom(aToZ);

}

private static String generateRandom(String aToZ) {
    Random rand=new Random();
    StringBuilder res=new StringBuilder();
    for (int i = 0; i < 17; i++) {
       int randIndex=rand.nextInt(aToZ.length()); 
       res.append(aToZ.charAt(randIndex));            
    }
    return res.toString();
}