Java Data Objects

Reader java1dev submits the following brief review of O'Reilly's Java Data Objects, which he says provides excellent coverage of JDO. His capsule description of the book: "First, a high-level overview, followed by an in-depth coverage of the core features, and concluding by describing the more complex concepts in detail. Running throughout the book is an excellent intuitive example application that illustrates the features being covered." Read on for more of his review. Java Data Objects author David Jordan & Craig Russell pages 356 publisher O'Reilly & Associates rating 9 reviewer java1dev ISBN 0596002769 summary Excellent, example-filled introduction and practical guide to Java Data Objects.

Craig Russell, at Sun Microsystems, is the specification lead for JDO and David Jordan, at Object Identity, has been an active member of the JDO expert group since its inception.

Java Data Objects provides a thorough coverage of JDO and explains how it can be used in various architectures. The reader is expected to be familiar with Java but needs only a limited knowledge of databases. In brief, Java Data Objects (JDO) insulates you from needing to know a lot about databases. JDO permits you to develop applications using your preferred Java object-oriented model, without you having to write code to translate between Java objects and how the data is stored in the database--JDO takes care of all of that for you.

The first three chapters provide a high level overview of JDO by walking through a small application, exploring each of its interfaces at a high level, and introducing the architectures it might be used in. Even if you have been away from code for a while you will be able to follow most of the code example. You can stop here if you just want to understand what JDO is all about and where it can be used. These are recommended reading for a manager.

Chapters 4 through 9 are required reading if you want to start developing JDO applications. They really get you into JDO, so you can understand it and start using it. The first three of these cover how to define persistent classes and fields, how they can be mapped to various databases (done for you) and the class enhancement process (which makes a lot of JDO transparent to you). The next three (chapter 7 through 9) bring home the power of JDO. These cover how to connect with a database, establish a transaction context and create, read, query, update and delete database objects. The material is made concrete by illustrating it with a detailed and intuitive example application. This example is carried throughout the book with sections of it explained as the concepts are covered.

Each remaining chapter covers a different JDO concept or feature (including optional features) that were introduced earlier but not covered in detail to keep the earlier chapters more understandable. These remaining topics are identity, lifecycle states & transitions, field management, cache management, nontransactional access and optimistic transactions. You can read these chapters as you feel the need for a more in-depth understanding of these concepts.

The last two chapters explain how to use JDO in an application-server environment and an Enterprise Java Beans environment. These two chapters assume you are already familiar with these environments, but I think a lot of it is understandable even if you are not.

There are five appendices with everything from the lifecycle state transitions to the collected source code for many of the classes used in the example application.

You can purchase Java Data Objects from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

Well, for those who missed it

[WndrBr3d]

I've said it once, and i'll say it again.

These book reviews on Slashdot, at times informative, really just are letting people know about the book and not as much reviewing that.

This demonstrated is that in the last two months, no book has received less than a 80% approval rating by the author (unless you rate a 'very good' as < 8). It's like Homer Simpson is writing these reviews, "This (book) gets my lowest rating ever, seven thumbs up."

I mean honestly, a review needs to have a few lemons on its record. I think someone should review a Wrox book on Linux and have it summarized with, "This book really gobbled the cob. it wouldn't be fit to line the kitchen floor for my puppy to soil in the evenings."

Instead of calling it 'Slashdot Book Review', it should just be called 'Slashdots list of books that rule'.

That's just my opinion though, I could be wrong.

Re:JDO vs EJB Entity Beans?

[awhite]

While it was widely used in designs a year ago, JDO will probably go down in history as the proverbial chicken that crossed the road when the CMP2.0 truck came along.

If you read a lot of Marc Fleury's public comments carefully, it is clear that he doesn't know what JDO is. He equates JDO with Castor JDO, which is a relatively simplistic persistence solution that happens to have "JDO" in its name; it is not a Java Data Objects implementation. The quote above is a perfect example: the JDO spec is barely a year old! So JDO was not widely used a year ago: Castor, however, was getting a lot of publicity around that time.

Fleury would do well to research the JDO spec, because a lot of the things he's proposing in his new vision for CMP are things that real JDO already does. JDO can persist vanilla Java classes with no code changes. Persistent fields and relations are completely transparent. Just declare a field of some other persistent type, and the relation is managed for you. Same with Collections and Maps and so forth (including collections and maps of relations to other objects). Data is lazily loaded as you access it, and change tracking is automatic. The runtime API for managing persisting objects consists of only a few classes. The query language looks just like Java boolean expressions. The whole system is elegant, but powerful. It stays out of your way. It's everything EJB is not :)