FAQ: Validating Email Addresses before sending

Question

Hi All!
Recently I've been developing a servlet to allow our users to change their email address. The problem with this, of course, is that the user can easily enter an invalid address or simply make an error typing their address. Obviously it's not possible to catch every error, but it is possible to at least verify that the address entered is of a valid format, i.e. [email protected]
The JavaMail API provides some validation in InternetAddress, but again allows some things to slip through the cracks. Here's the code that I've come up with to at least ensure the proper email address format:
import javax.mail.internet.InternetAddress;
import java.net.InetAddress;
public static boolean emailIsValid(String addr)
boolean result=true;
try {
int atPos=addr.indexOf("@");
String host=addr.substring(atPos+1,addr.length());
InternetAddress validAddr = new InternetAddress(addr);
InetAddress inet = InetAddress.getByName(host);
catch (Exception e) {
result=false;
return result;
}The drawback to this solution is that IP address/host name combinations are cached in a static map in the JVM. This means the more hosts that get mapped, the more memory is required by the JVM to cache these hosts in its static Map.
On the other hand, the only time this map should grow is when an email address gets changed, and the address is moved to a previously unknown domain. Hopefully, the memory requirements should not become unbearable during the expected uptime for the JVM.
Hopefully this will help a few people out...!
--David Hibbs

Answer 1

Minor code modification:
try {
inet = java.net.InetAddress.getByName(host);
catch (Exception e) {
inet = java.net.InetAddress.getByName("www." + host);
}This lets domains that don't have an IP entry for their top level but still have a web presence to be considered valid.