Java Apache Mail Enterprise Server

Mail servlets do not specify how they are mapped and accessed by the clients. A possible implementation (that will be used in Apache James) is the mapping of virtual mailboxes to a specified mail servlet.

Let us suppose we want to create a mailing list in a mailservlet-enable mail system. Our mail server is listening on the SMTP port on the host java.apache.org. We want the address james-dev@java.apache.org to be the Apache James development mailing list.

Let's write the MailingListServlet as follows (note that since we are not allowed to use the javax package, we will use org.apache until JavaSoft incorporates them officially into the servlet API framework, if this ever happens)

import javax.servlet.*;
import org.apache.servlet.mail.*;
import java.io.*;

/**
* This servlet implements a general mailing list engine that could
* be used to handle many simultaneous mailing list backended by
* a database of names.
*
* @author Stefano Mazzocchi
* @author Pierpaolo Fumagalli
*/
public class MailingListServlet extends MailServlet {

public void service(MailServletRequest req, MailServletResponse res) 
throws ServletException, IOException {
    
    // Get headers from the incoming mail
    MailHeaders headers = req.getHeaders();

    // Get the address this servlet is currently serving
    // This is used by the servlet to know which mailing list
    // have been requested.
    MailAddress list = req.getServletAddress();

    // Get the mail sender
    MailAddress sender = req.getSender();

    String subject = headers.getSubject().toLowerCase();

    // The sender of this mail is always the list.
    res.setSender(list);

    if (subject.startsWith("subscribe")) {
       res.setRecipient(sender);
       if (addSubscriber(list, sender)) {
          headers.setSubject("Welcome");
          res.getOutputStream().println("Welcome to the list!");
       } else {
          headers.setSubject("You're already listed");
          res.getOutputStream().println("You are already subscribed to this list");
       }
    } else if (subject.startsWith("unsubscribe")) {
       res.setRecipient(sender);
       if (removeSubscriber(list, sender)) {
          headers.setSubject("Good bye");
          res.getOutputStream().println("We'll miss you!");
       } else {
          headers.setSubject("You are not subscribed");
          res.getOutputStream().println("You are not subscribed to this list");
       }
    } else if (this.isPresent(sender, list)) {
       // Get the names of the subscribers
       MailAddress[] subs = this.getSubscribers(list);

       // Every part of the request that is not touched by the mail servlet
       // is copied onto the response stream. In this case, the subject.

       // Set the recipients of this mail, hiding the list of the recipients
       res.setRecipients(subs, false);

       BufferedInputStream input = new BufferedInputStream(req.getInputStream());
       ServletOutputStream output = res.getOutputStream();

       // Copy the mail message
       int ch;
       while ((ch = input.read()) != -1) {
          output.write(ch);
       }

       // Append a signature to the message.
       output.println("\n--\nManaged by " + this.getServletInfo()); 
    } else {
       res.setRecipient(sender);
       headers.setSubject("Message Rejected");
       res.getOutputStream().println("Sorry, but you have to subscribe to the list " + 
          "to be allowed to send messages");
    }

    res.setHeaders(headers);
}

private MailAddress[] getSubscribers(MailAddress list) {
    // return the array of subscribers to this list
    return null; // for now
}

private boolean isPresent(MailAddress sender, MailAddress list) {
    return true; // if sender is present on the list
}

private boolean addSubscriber(MailAddress list, MailAddress sender) {
    // add sender from the list associated to the list mail address
    // this could use JDBC or whatever to keep track of these changes.

    return true; // if name wasn't present and got included
}

private boolean removeSubscriber(MailAddress list, MailAddress sender) {
    // add sender from the list associated to the list mail address
    // this could use JDBC or whatever to keep track of these changes.

    return true; // if name was present and got removed
}

public String getServletInfo() {
    return "Mailing List Servlet ver. 0.1";
}
}

Once this mail servlet is written and compiled, it can be mapped to the james-dev mailbox of the mail server using the appropriate configurations and creating the appropriate database tables in the JDBC connected database used by this servlet.

As you see, a powerful and highly flexible mailing list system can be created with just a few lines of work and can be ported on any mail-servlet enabled mail server.

Mail Servlet API Extentions

Introduction

The goals

The design

A possible implementation

A detailed look at the proposal

Future directions