Chapter 12. JDO

We say that error is appearance. This is false. On the contrary, appearance is always true if we confine ourselves to it. Appearance is being.

”Jean-Paul Sartre, Truth and Existence

Java Data Objects (JDO) is one of the first APIs to run through the Java Community Process (JCP). JDO enables application developers to build applications without worrying about persistence issues. In other words, it does for your application the same thing EJB container-managed persistence does for EJB applications. Where EJB seeks to deliver all the features of enterprise systems development ”such as a distributed component model and full and distributed transaction management ”JDO seeks to provide developers with a more streamlined set of features.

JDO seeks to give applications with persistence needs the following capabilities:

• Simplicity

• Database independence

• Performance

In other words, JDO is a database-independent persistence API that has a simple programming model designed to support the performance needs of common applications. Though EJB is database-independent, it does not have a simple programming model and performs poorly for small- to medium-scale applications.

Software Requirements

JDO is not a standard part of any Java platform. You therefore need a host of tools to support JDO development. Naturally, you need a data store. You also need a JDO implementation. Depending on the nature of the implementation, you may need a JDBC driver or any other of a number of third-party components .

The best way to get started is to download Sun's reference JDO implementation at http://java.sun.com/products/jdo. It uses your filesystem as a data store and frees you from needing anything else while you are learning JDO.