The JavaMail API offers a clean object-oriented framework of classes that model a theoretical mail system. JavaMail is platform-independent and protocol-independent, and therefore presents an ideal way to build e-mail and messaging solutions that will work with WAP technology.
Many applications can benefit from e-mail support; using JavaMail, developers can rapidly construct messaging functionality whilst abstracting the underlying vendor's implementation in a similar way to the abstraction achieved from relational databases with JDBC.
In many ways the JavaMail service providers act in a similar way to those that provide JDBC drivers, doing for SMTP, Lotus Notes etc, what JDBC does for Oracle and Sybase. In our examples we use the SMTP and POP3 drivers provided by Sun.
JavaMail models an abstract messaging service and any vendor specific mail system that provides a JavaMail interface implementation can be accessed with minimal –(ideally no) – recoding.
Next we are going to take a look at some examples that make use of e-mail capabilities using JavaMail. The first example will show how an m-commerce application can use SMTP to send an e-mail confirming to the customers that their order has been placed, and the second example will utilize SMTP and POP3 to code a WAP based web mail application.
The following sections assume a basic working knowledge of Java Servlets. These were introduced in Chapter 10, but for more detailed information, see Java Server Programming by Andrew Patzer et al, published by Wrox.ISBN 1861002777
All the examples in this chapter were tested under Microsoft Windows NT version 4.0, service pack 5, and Windows 98 and Windows 2000. You will need to download and install the following software to compile and run the examples in the rest of this chapter:
q JDK (Java Development Kit) 1.2.2. Download from http://java.sun.com/jdk/
q JSDK (Java Servlet Development Kit) 2.1. Download from http://java.sun.com/products/ (This is also available in the JSWDK download)
q JAF (Java Activation Framework). Download from http://java.sun.com/beans/glasgow/jaf.html
q Java Mail 1.1.3, which includes an SMTP service provider. Download from http://java.sun.com/products/javamail
q Java Mail POP3 provider. Separate download from http://java.sun.com/products/javamail/pop3.html
You will also need to have access to a web server, in which to deploy the Java servlets we will write, and a WAP browser emulator, to test the code. In this chapter we used:
q Gefion Web Server Lite (http://www.gefionsoftware.com/LiteWebServer/)
q Phone.com UP.SDK 4.0 beta 2 Simulator (http://www.phone.com)
Access to a SMTP server and a POP3 server is also needed. You can find out your POP3 and SMTP host names by contacting your Internet Service Provider or network administrator. They will be similar to the following:
q
pop.yourISP.net
q
smtp.yourISP.net
You will need to add the following jar files to your Java environment's CLASSPATH variable in order to compile the example.
Under Windows 95/98 the relevant CLASSPATH amendments can be made in your autoexec.bat:
CLASSPATH = C:\jaf-1.0.1\activation.jar;
CLASSPATH = %CLASSPATH%;c:\jsdk2.1\servlet.jar;
CLASSPATH = %CLASSPATH%;c:\pop3-1.1.1\pop3.jar;
CLASSPATH = %CLASSPATH%;c:\javamail-1.1.3\mail.jar;
CLASSPATH = %CLASSPATH%;c:\jdk1.2.2\lib\WML.jar;
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Under Windows NT, you can make the necessary changes by right-mouse clicking on the My Computer icon on your desktop and choosing Properties, or opening the System icon in the Control Panel. The Classpath environment variable can then be added or modified in the Environment tab: |
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To configure your web server to work with the WAP MIME types you must add the WAP MIME types to the web server's configuration files, as was discussed in Chapter 2.
The JavaMail API leverages the capabilities for dealing with complex data types from the Java Activation Framework (JAF), which is part of the Glasgow JavaBeans specification. JAF provides Java with similar capabilities that plug-ins provide for web browsers. The Java Activation Framework allows for the querying and handling of multi-media data types, although this is of limited use on the current generation of WAP-enabled phones.
As more advanced and richer featured devices become available, JAF will provide the programming framework needed to integrate our e-mail application with the functionality of MIME. Enhancing the next generation of wireless devices to utilize complex mail attachments will be a trivial step using JAF, but will be a critical step in making WAP devices a must have commodity item.
We will now introduce some of the most important JavaMail classes that we will see in used in
later examples.
The javax.mail.Session class (not to be confused with the javax.servlet.http.HttpSession class) is used to control access to the implementations of the other mail classes that represent the services offered by the mail system, for instance javax.mail.Store.
This class is used for sending mail messages via a specific protocol such as SMTP, as implemented by the service provider.
This class is implemented by the service provider. It aims to allow access to read, write, monitor, and search activities for a particular mail protocol such as POP3, or IMAP4. A reference to the javax.mail.Folder class is obtained via this class.
The javax.mail.Folder class gives a hierarchical view of javax.mail.Message objects, and provides access to specific messages for read, delete and reply actions.
This class models the actual mail message. The javax.mail.internet.MimeMessage class holds very little information and data about the message when it is first instantiated; as successive methods retrieve more data about the message, this class is used to store that data.
This lightweight message structure – populating the message with data only as it is needed – is an advantage when you wish to scroll through lists of message headers in your inbox without downloading the whole of each item. If a message contains a 10Mb attachment, this need only be retrieved when it is required, which considerably increases the speed of viewing lists of messages on a first generation GSM WAP phone!
The ability to download the attributes of a message, and not its entire contents, is optional for compliance with the POP3 protocol. However, most POP3 implementations allow for this partial retrieval of message information, enabling the JavaMail implementation to take advantage of
this feature.
This class models a RFC822 e-mail address, i.e. an address of the form john_doe@wapbook.org. If an incorrect address format is encountered an error occurs, and an AddressException is thrown, within the Java method processing the e-mail address.
We will now take a quick look at a class designed to make the generation of WML easier for the servlet to handle. We can do this by providing a class that models the creation of WML, abstracting out some routine tasks such as generating the WML header, and opening, and closing both cards and the deck itself.
