Java Network Programming, Second Edition

Folders

So far, we’ve worked mostly with the INBOX folder. This is the default folder where most mail resides until the user filters or saves it into some other folder. On some systems, it may actually reside in a file called INBOX. On other systems, it may be called something different. Nonetheless, you can always access it from the JavaMail API using the name INBOX.

Most mail programs do allow you to organize your messages into different folders. These folders are hierarchical; that is, one folder may contain another folder. In particular, in the IMAP protocol, servers store the messages in different folders, from which clients retrieve and manipulate the messages as necessary. POP servers, by contrast, generally send all the messages to the user when the user connects, then rely on the client to store and manage them. The primary advantage of the IMAP approach over POP is that it allows a user to easily access his entire email archive from multiple client machines.

The JavaMail API represents IMAP-like folders as instances of the abstract Folder class:

public abstract class Folder extends Object

This class declares methods for requesting named folders from servers, deleting messages from folders, searching for particular messages in folders, listing the messages in a folder, and so forth. Most of these methods are declared abstract. When you ask a session, a store, or a folder to give you one of the folders it contains, it will give you an instance of a concrete subclass appropriate ...