How to generate random alphanumeric string of given size in Java

In this section, we will show you how to generate random alphanumeric string of given size in Java.


Example 1: Use SecureRandom

import java.security.SecureRandom;

public class Main {

    //Create a String of the characters which can be included in the string
    private static final String ALPHA_NUMERIC_STRING  =
            "ABCDEFGHIJKLMNOPQRSTUVWXY" +
                    "Zabcdefghijklmnopqrstuvwxyz0123456789";

    // Driver code
    public static void main(String[] args)
    {
        String randomAlphaNumericString = generateAlphaNumericString(25);
        System.out.println(randomAlphaNumericString);
    }

    //Method to generate Random AlphaNumeric String
    public static String generateAlphaNumericString(int length) {

        SecureRandom random = new SecureRandom();
        StringBuilder builder = new StringBuilder(length);

        for (int i = 0; i < length; i++) {
            builder.append(ALPHA_NUMERIC_STRING.
                    charAt(random.nextInt(ALPHA_NUMERIC_STRING.length())));
        }

        return builder.toString();
    }
}

Console Output:
97Iv8KBcDHntD0nv8rj1964L1


Example 2: Apache Commons Text library

Download Apache Commons Text library:

<dependency>
   <groupId>org.apache.commons</groupId>
   <artifactId>commons-text</artifactId>
   <version>1.10.0</version>
</dependency>

Main.java:

import org.apache.commons.text.CharacterPredicates;
import org.apache.commons.text.RandomStringGenerator;

public class Main {

    // Driver code
    public static void main(String[] args)
    {
        String randomAlphaNumericString = generateAlphaNumericString(25);
        System.out.println(randomAlphaNumericString);
    }

    //Method to generate Random AlphaNumeric String
    public static String generateAlphaNumericString(int length) {

        RandomStringGenerator randomStringGenerator =
                new RandomStringGenerator.Builder()
                        .withinRange('0', 'z')
                        .filteredBy(CharacterPredicates.LETTERS, 
                                CharacterPredicates.DIGITS)
                        .build();
        return randomStringGenerator.generate(length);
    }
}

Console Output:
cJWQyrKznpxXpVJXeVwlI5aVb

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