Design: Emailing System in Java

Question

Hi everyone,

I'm building an emailing system for a framework I'm developing. Thus far, I've got a generic MailMessage interface that every different type of email message will implement, something along the lines of

public interface MailMessage {
    public String[] getTo();
    public void setTo(String[] to);
    public String getFrom();
    public void setFrom(String from);
    ...
    // you can guess the setters/getters here
    ...
}

I've then got a SimpleMailMessage that's exactly what you would expect as a simple implementation of the interface (no encryption or encoding, just plain text).

I've created an MailMessageFactory interface that's used as an abstract factory. I've got a SimpleMailMessageFactory that implements the factory to produce instances of SimpleMailMessage.

One type of email I'd like to the framework to send is an Alert mail message, that is essentially a regular mail message except with "[Alert]" prefixed to the subject line (Another might be a email containing a "list" of order items, but I'm not sure of where the responsibility falls for converting the list to a String for an email lies). I can either subclass the SimpleMailMessage and override the setSubject(String subject) method to something like

public class AlertMailMessage {
    ...
    public void setSuject(String subject) {
        this.to = "[Alert]" + to;
    }
    ...
}

Or I can create a decorator:

public abstract class EmailDecorator implements MailMessage {
    protected MailMessage email;
    ...
    // delegate all implemented methods to email
    ...
}

public class AlertEmailDecorator extends EmailDecorator {
    public void setSubject(String subject) {
        email.setSubject("[Alert]" + subject);
    }
}

Or I can just delegate adding the "[Alert]" string in the SimpleMailMessageFactory.

Thoughts on what I have? I think the problem is that I might be too thoughtful and forward-thinking, but I want the perfect design.

Answer 1

The decorator seems like the better option. However, why are you writing your own email framework for Java? Why not just use the JavaMail API?

Answer 2

A decorator seems a better option to me. I am thinking of, may be you need to append your subject line with, Fwd: or Re: as well, or may be you need to support signature where you will be adding a signature to the email body.

Answer 3

Sounds just like the Spring's support for JavaMail. Don't reinvent the wheel, use already existing, proven solutions, and build on top of that.