Is it possible to validate IMEI Number?

Question

For a mobile shop application, I need to validate an IMEI number. I know how to validate based on input length, but is their any other mechanism for validating the input number?

Answer 1

According to the previous answer from Karl Nicoll i'm created this method in Java.

public static int validateImei(String imei) {

    //si la longitud del imei es distinta de 15 es invalido
    if (imei.length() != 15)
        return CheckImei.SHORT_IMEI;

    //si el imei contiene letras es invalido
    if (!PhoneNumber.allNumbers(imei))
        return CheckImei.MALFORMED_IMEI;

    //obtener el ultimo digito como numero
    int last = imei.charAt(14) - 48;

    //duplicar cada segundo digito
    //sumar cada uno de los digitos resultantes del nuevo imei
    int curr;
    int sum = 0;
    for (int i = 0; i < 14; i++) {
        curr = imei.charAt(i) - 48;
        if (i % 2 != 0){
            // sum += duplicateAndSum(curr);
            // initial code from Osvel Alvarez Jacomino contains 'duplicateAndSum' method.
            // replacing it with the implementation down here:
            curr = 2 * curr;
            if(curr > 9) {
                curr = (curr / 10) + (curr - 10);
            }
            sum += curr;
        }
        else {
            sum += curr;
        }

    }

    //redondear al multiplo de 10 superior mas cercano
    int round = sum % 10 == 0 ? sum : ((sum / 10 + 1) * 10);

    return (round - sum == last) ? CheckImei.VALID_IMEI_NO_NETWORK : CheckImei.INVALID_IMEI;

}