I am using a very simple solution using Java 8. Just customize it according to your needs.
...import java.security.SecureRandom;...//Generate a random String of length between 10 to 20.//Length is also randomly generated here.SecureRandom random = new SecureRandom();String sampleSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_";int stringLength = random.ints(1, 10, 21).mapToObj(x -> x).reduce((a, b) -> a).get();String randomString = random.ints(stringLength, 0, sampleSet.length() - 1) .mapToObj(x -> sampleSet.charAt(x)) .collect(Collector .of(StringBuilder::new, StringBuilder::append, StringBuilder::append, StringBuilder::toString));We can use this to generate an alphanumeric random String like this (the returned String will mandatorily have some non-numeric characters as well as some numeric characters):
public String generateRandomString() { String sampleSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_"; String sampleSetNumeric = "0123456789"; String randomString = getRandomString(sampleSet, 10, 21); String randomStringNumeric = getRandomString(sampleSetNumeric, 10, 21); randomString = randomString + randomStringNumeric; //Convert String to List<Character> List<Character> list = randomString.chars() .mapToObj(x -> (char)x) .collect(Collectors.toList()); Collections.shuffle(list); //This is needed to force a non-numeric character as the first String //Skip this for() if you don't need this logic for(;;) { if(Character.isDigit(list.get(0))) Collections.shuffle(list); else break; } //Convert List<Character> to String randomString = list.stream() .map(String::valueOf) .collect(Collectors.joining()); return randomString;}//Generate a random number between the lower bound (inclusive) and upper bound (exclusive)private int getRandomLength(int min, int max) { SecureRandom random = new SecureRandom(); return random.ints(1, min, max).mapToObj(x -> x).reduce((a, b) -> a).get();}//Generate a random String from the given sample string, having a random length between the lower bound (inclusive) and upper bound (exclusive)private String getRandomString(String sampleSet, int min, int max) { SecureRandom random = new SecureRandom(); return random.ints(getRandomLength(min, max), 0, sampleSet.length() - 1) .mapToObj(x -> sampleSet.charAt(x)) .collect(Collector .of(StringBuilder::new, StringBuilder::append, StringBuilder::append, StringBuilder::toString));}
