Recently, I helped one of our customers migrating a legacy database to Hibernate;
one of the more interesting topics was versioning and audit logging. Actually, in the
last couple of months, the subject of historical data came up several times. No
matter if it was a legacy SQL schema or a migration from a broken object-oriented
database, everyone had their own way to log data changes.
Abe White of Solarmetric replies to my criticisms of JDO on TSS. I'm actually not interested in getting into a lengthy debate over this, but since there /was/ an error in my first post, I must certainly acknowledge that.
Yesterday, Linda DeMichiel announced the changes coming in EJB 3.0. There was a lot to digest in her presentation, and I think it will take a while for people to figure out the full implications of the new spec. So far, most attention has focused upon the redesign of entity beans, but that is most certainly not all that is new! The expert group has embraced annotations aggressively, finally eliminating deployment descriptor XML hell. Taking a leaf from Avalon, Pico, Spring, Hivemind, etc, EJB will use dependency injection as an alternative to JNDI lookups. Session beans will be POJOs, with a business interface, home objects have been eliminated. Along with various other changes, this means that EJB 3.0 will be a much more appropriate solution for web-based applications with servlets and business logic colocated in the same process (which is by far the most sane deployment topology for most - but not all - applications), without losing the ability to handle more complex distributed physical architectures.
Maybe you haven't noticed, but every single piece of information on JDK 1.5 Metadata
Annotations is nothing but a simple /Hello World/ tutorial (of course, I exclude the
specification). There is no real world implementation. This is especially true for
codes processing the annotations. I'll call such an application an annotation reader.
Like, I suppose, many Java developers, I have so often read about the supposed scalability problems associated with stateful session beans, that I simply accepted that these problems were real, and refused to even consider using stateful beans. I guess this was laziness, but we don't have time to verify everything we read - and I'd never had cause to doubt that what I read was correct.
After more than a year of activity, development of the Hibernate2 branch has finally been wound up; Hibernate 2.1.3 will be one of the last releases and represents a rock-solid POJO persistence solution with essentially all the functionality needed by a typical Java application. Any future release of Hibernate 2.1 will contain only bugfixes. The branch that we have been calling 2.2, will actually be released as version 3.
If you ever work with relational databases, you should go out and buy O'Reilly's
/SQL Tuning/, by Dan Tow. The book is all about how to represent a SQL query in a
graphical form and then, using some simple rules of thumb, determine an optimal
execution plan for the query. Once you have found the optimal execution plan, you
can add indexes, query hints, or use some other tricks to persuade your database
to use this execution plan. Fantastic stuff. There is even sufficient introductory
material for those of us (especially me) who know less than we should about the
actual technical details of full table scans, index scans, nested loops joins,
hash joins, etcetera to be able to start feeling confident reading and understanding
execution plans. Unlike most database books out there, this book is not very
platform-specific, though it does often refer specifically to Oracle, DB2 and SQL
Developerworks is featuring the best article
I have ever read on the subject of Java performance. The authors dispose of the
canard that temporary object creation is expensive in Java, by explaining how
generational garbage collection works in the Sun JVM (this is a bit more detailed
explanation than the typical one, by the way). Well, I already knew this; Hibernate
rejected the notion of object pooling right from the start (unfortunately, the
EJB spec has not yet caught up).
Currently I have noticed that Naked Objects gets more and more blog-time.
And every time I wondered why (many?) people found it so intriguing -
and I often thought about making a blog about the good and bad about Naked Objects;
but I've never found the time.