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The Doc-u-Matic application illustrates JNDI's support for:
Note: To download the complete source code for this article, see Resources.
Doc-u-Matic is first-and-foremost a demonstration of JNDI-supported object persistence. Therefore, I think it makes sense to begin with a review of JNDI's support for stored objects.
You may recall from March's column that there are three techniques for storing Java objects in a JNDI service: as serialized data, as a reference to an object, and as the attributes on a directory context. Storing an object as serialized data is the simplest of the three techniques. Storing an object as a reference is useful in situations in which it doesn't make sense (or isn't possible) to store actual objects. Finally, storing objects as attributes on a directory context is useful when other, non-Java applications need access to the object's information. The application I've developed uses the first two methods of object storage.
Figure 1, below, illustrates Doc-u-Matic from a functional perspective. Doc-u-Matic consists of three major functional units: the JNDI service (of course), a library service, and one or more clients.
Figure 1. Doc-u-Matic: A functional view
A library is a place to which you publish objects and from which you retrieve them. An object can be any Java instance, as long as it supports one of the storage methods mentioned above -- it can be a String, a JavaBean, and so on.
JNDI plays two roles in Doc-u-Matic. It provides a single, well-known location where clients can locate the library service (standard address-book functionality), and it supports the implementation of the library service itself. On the latter point, it's worth noting that nothing in the design of a library implies that it has to be implemented on top of JNDI -- that's just the direction I took (since this is an article on JNDI). You could implement a library on top of any technology that provides support for publishing and retrieving information, including HTTP, JDBC, NNTP, or IMAP. Best of all, the clients would never know the difference.
Doc-u-Matic assumes you have obtained, or have access to, and have configured an LDAP service. The application should support any naming and directory service that provides a JNDI service provider. However, I will assume you're using LDAP.