The following code is a sample of some characters you can check are in an email address, or should not be in an email address. It is not a complete email validation program that checks for all possible email scenarios, but can be added to as needed.


/*
* Checks for invalid characters
* in email addresses
*/
public class EmailValidation {
public static void main(String[] args)
throws Exception {

String input = "@sun.com";
//Checks for email addresses starting with
//inappropriate symbols like dots or @ signs.
Pattern p = Pattern.compile("^.|^@");
Matcher m = p.matcher(input);
if (m.find())
System.err.println("Email addresses don´t start" +
" with dots or @ signs.");
//Checks for email addresses that start with
//www. and prints a message if it does.
p = Pattern.compile("^www.");
m = p.matcher(input);
if (m.find()) {
System.out.println("Email addresses don´t start" +
" with "www.", only web pages do.");
}
p = Pattern.compile("[^A-Za-z0-9.@_-~#]+");
m = p.matcher(input);
StringBuffer sb = new StringBuffer();
boolean result = m.find();
boolean deletedIllegalChars = false;

while(result) {
deletedIllegalChars = true;
m.appendReplacement(sb, "");
result = m.find();
}

// Add the last segment of input to the new String
m.appendTail(sb);

input = sb.toString();

if (deletedIllegalChars) {
System.out.println("It contained incorrect characters" +
" , such as spaces or commas.");
}
}
}