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The regular Expression about Email Validation

public static boolean isValidEmailAddress(String emailAddress) {
*  1. ^(caret): Matches at the start of the string the regex pattern is applied to.
*  2. \ (backslash) followed by any of ^-]\ : A backslash escapes special characters to suppress their special meaning.
*  3. () The ( (open parenthesis) and ) (close parenthesis) may be used to group (or bind) parts of our search expression together
*  4. * The * (asterisk or star) matches the preceding character 0 or more times, for example, tre* will find tree (2 times) and tread (1 time) and trough (0 times).
*  5. + The + (plus) matches the previous character 1 or more times, for example, tre+ will find tree (2 times) and tread (1 time) but not trough (0 times).

String expression = "^[\\w\\-]([\\.\\w])*[\\w]*@([\\w\\-]+\\.)+[A-Z]{2,4}$";

CharSequence inputStr = emailAddress;
Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(inputStr);
return matcher.matches();

 public static void main(String args[]){
    System.out.println("1:" + isValidEmailAddress(""));
    System.out.println("2:" +isValidEmailAddress(""));
    System.out.println("3:" +isValidEmailAddress(""));
    System.out.println("4:" +isValidEmailAddress(""));
    System.out.println("5:" +isValidEmailAddress(""));
    System.out.println("6:" +isValidEmailAddress(""));
    System.out.println("7:" +isValidEmailAddress(""));
    System.out.println("8:" +isValidEmailAddress(""));
    System.out.println("9:" +isValidEmailAddress(""));
    System.out.println("10:" +isValidEmailAddress(""));
    System.out.println("11:" +isValidEmailAddress("!!!"));
    System.out.println("12:" +isValidEmailAddress(""));



Comments: this is just for your information. The regular expression I used is bad. I implement this email Valiator function by changing the source code of apache common Email Validator finally.


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