java判断正整数

public static boolean isPureDigital(String str) {
    if (str == null || "".equals(str)){
        return false;
    }

    Pattern p;
    Matcher m;
    p = Pattern.compile("[0-9]*");
    m = p.matcher(str);
    if (m.matches()){
        return true;
    }else{
        return false;
    }
}