How to check if a letter is (a-z or A-Z) in Java?

Question

The issue that I have is, I have a string input (s), which I then need to split by anything that is not (a-z or A-Z). The solution I've found so far is to split the String by empty spaces, but I've realised it will be more efficient to split by any non-alphabetical characters. This would then allow me to instantly output the array.

Question:

My question is, how do I split a string by any character in a string.

I basically need a version of this:

String[] inputSplit = input.split(" ", "!", ",", "?", ".", "_", "'", "@");

but it actually works without errors.

The code I've written so far isn't really relevant to the question, but I'll put it here anyway in case it helps:

import java.util.Arrays;
import java.util.Scanner;

public class StringTokens {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String input = scan.nextLine();
        // Splits by " "
        String[] inputSplit = input.split(" ");
        // Counts the amount of tokens
        int n = inputSplit.length;

        System.out.println(n);
        for (int i = 0; i < inputSplit.length; i++) {
            // Prints each of the items in the array
            System.out.println(inputSplit[i]);
        }
    }
}