You may utilize AspectJ in your application.
I can't help you any further on how to configure and setting it up

You can use JavaMail API to quench your desire.

He pointed out that he wants to send  email AUTOMATICALLY and JavaMail doesn't support
such feature individually, so the answer is AspectJ

I noticed to this point but if he wanna send  mail with pure java  he can use JavaMail API like this :

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.*;

public class MailSender {
public void postMail(String smtpsrv, String recipients[], String subject,
String message, String from) throws MessagingException {
boolean debug = false;

//Set the host smtp address
Properties props = new Properties();
props.put("mail.smtp.host", smtpsrv);

// create some properties and get the default Session
Session session = Session.getDefaultInstance(props, null);
session.setDebug(debug);

// create a message
Message msg = new MimeMessage(session);
// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);

InternetAddress addressTo[]= new InternetAddress[recipients.length];
addressTo= new InternetAddress[recipients.length];
for (int i = 0; i < recipients.length; i++) 
{
addressTo= new InternetAddress(recipients);
}
msg.setRecipients(Message.RecipientType.TO,addressTo);

// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message, "text/html;charset=utf-8");
Transport.send(msg);
}

} 

i assume that u have any application server , like Tomcat Or Jboss .
in either of them u can define your servlet  inside web.xml file as below :

    <servlet>
        <servlet-name>SchadulerServlet</servlet-name>
        <servlet-class>schaduler.SchadulerServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>SchadulerServlet</servlet-name>
        <url-pattern>/US</url-pattern>
    </servlet-mapping>

you can use JavaMail API for sending mail
but the better approach is apache common email  component which is
simple abstract API on java  mail,
if you need a scheduling system that automatically send  mail you can use
scheduling framework such as Quartz and if you want to send mail
automatically based on some action you can use aspect frameworks.

http://commons.apache.org/email/