Question

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How to generate a random String in Java

I am wanting to generate a random string of 20 characters without using apache classes. I don’t really care about whether is alphanumeric or not. Also, I am going to convert it to an array of bytes later FYI.

Thanks,

Answer 1

Here you go. Just specify the chars you want to allow on the first line.

char[] chars = "abcdefghijklmnopqrstuvwxyz".toCharArray();
StringBuilder sb = new StringBuilder(20);
Random random = new Random();
for (int i = 0; i < 20; i++) {
    char c = chars[random.nextInt(chars.length)];
    sb.append(c);
}
String output = sb.toString();
System.out.println(output);

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If you are using this to generate something sensitive like a password
reset URL or session ID cookie or temporary password reset, be sure to use
java.security.SecureRandom instead.
Values produced by java.util.Random and java.util.concurrent.ThreadLocalRandom are mathematically predictable.