Delete all special characters except for some

I guess what you need is to validate the email, for that java has its established method, which is quite useful (I sense it because I try to do it that way too and the laughs)

The method in question is isValidEmailAddress and it is already responsible for cleaning the String that you have to enter as a parameter, if it does not exist you have to capture the exception

public static boolean isValidEmailAddress(String email) {
 boolean result = true;
 try 
 {
   InternetAddress emailAddr = new InternetAddress(email);
   emailAddr.validate();
 } 
 catch (AddressException ex) 
 {
    result = false;
 }
    return result;
 }

And if you do not want to use the methods provided by java. You can use a standardized pattern, which I add below

import java.util.regex.Matcher; import java.util.regex.Pattern;

public class Main {
public static void main(String[] args) {

    // Patrón para validar el email
    Pattern pattern = Pattern
            .compile("^[_A-Za-z0-9-\+]+(\.[_A-Za-z0-9-]+)*@"
                    + "[A-Za-z0-9-]+(\.[A-Za-z0-9]+)*(\.[A-Za-z]{2,})$");

    // El email a validar
    String email = "[email protected]";

    Matcher mather = pattern.matcher(email);

    if (mather.find() == true) {
        System.out.println("El email ingresado es válido.");
    } else {
        System.out.println("El email ingresado es inválido.");
    }
}

Suppose you have the email received from an object called mail

final String email = validarString(correo.getEmail(), 100);

I use the following method to validate that if it is mail type but also that it does not exceed 100 characters in length:

public String validarString(String campo, long longitud_maxima) {

    String filtro = campo;
    Pattern patron = Pattern.compile("[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}");
    Matcher mat3 = patron.matcher(campo);

    if(mat3.matches()){
        //si el correo coincide, no haga nada, pero significa que pasó la validación
    }else{ //si el corrreo está mal escrito, devolvemos un null
    return null;
        } //fin validación email

        //validamos longitud mínima
        if (campo.length() == 0) {
            return null;
        }

        //validamos si el usuario envía varios espacios en blanco
        int whitespace_counter = 0;
        for (int i = 0; i < campo.length(); i++) {
            if (Character.isWhitespace(campo.charAt(i))) {
                whitespace_counter++;
            }
        }

        if(campo.length() == whitespace_counter) {
            return null;
        }


    //validamos longitud máxima
    if(campo.length() > longitud_maxima) {
        return null;
    }
    return filtro;
}