Java Easy Mail Sender

Abo

Many applications need to send e-mail messages, for everything from server status updates to marketing messages, and some of these include photos, charts, or other images. You certainly have received plenty of email that contains images, but you may not know programmatically how to send such a thing from your Java code. In this article, I show the basics of using JavaMail, how to send HTML messages, and how to use MIME to create a multipart message that encloses the images, either as attachments, or as part of the message body.

The easiest way to send email with Java is by using a library provided by Oracle. There are a few jar files in the distribution. The simplest thing to do is to use mail.jar, since it contains the whole API and several transport implementations. Another jar file contains only the API, and Oracle broke down the implementations for each transport into its own jar file. You can pick-and-choose to suit your application’s needs. For example, if you send email from an applet, you would only include mailapi.jar and smtp.jar.

Note that some Java frameworks have features that make it even easier to send email. For example, the Spring Framework includes an API that provides a layer of abstraction over JavaMail. The Play Framework, on the other hand, provides a plugin to send email.

So, your very first step, even before writing a line of code, is to make sure you have the mail.jar or the various jar files you chose in your classpath, and take whatever other steps are required to make sure to include the jar file (or files) in your deployment process.

Creating a simple email message

The class that represents an email message in JavaMail is, unsurprisingly, javax.mail.Message. This is an abstract class, so we have to hunt down the specific subclass we need. Message only has one direct subclass in the API, javax.mail.internet.MimeMessage. You’d think it’s good news, since it’s not even abstract, but upon closer observation, you will discover that none of the constructors are public. So, we have to find another subclass to instantiate.

But first, why do we even want a MimeMessage?

Once upon a time, all you could send through email was plain text, and only 7-bit text at that. Now, thanks to MIME, the Multipurpose Internet Mail Extensions standard, we can send just about anything (short of chocolate cake). Email messages can contain multiple parts; each part can encode data of a different type. The message itself tells the recipient’s client how to split up the message data into parts, and how to treat each part.

Thus: We need to create a MimeMessage. Each transport has its own Message subclass, so we need to figure out which transport to use to send the message. The JavaMail API supports three widely used email protocols: SMTP, POP3, and IMAP. Out of those, only SMTP is a protocol specifically designed for sending messages; the other two are used to retrieve messages from a server, so the choice is obvious.

ut