Preface
Hibernate is a lightweight object/relational mapping service for Java.
What does that mean? It's a way to easily and efficiently work with
information from a relational database in the form of natural Java objects.
But that description doesn't come close to conveying how useful and
exciting the technology is. I'm not the only person who thinks so: Hibernate
2.1 just won Software Development magazine's 14th annual Jolt
Award in the 'Libraries, Frameworks, and Components' category.So, what's great about Hibernate? Every nontrivial application (and even
many trivial ones) needs to store and use information, and these days
this usually involves a relational database. Databases are a very different
world than Java objects, and they often involve people with different
skills and specializations. Bridging between the two worlds has been
important for a while, but it used to be quite complex and tedious.Most people start out struggling to write a few SQL queries, embedding
these awkwardly as strings within Java code, and working with JDBC to
run them and process the results. JDBC has evolved into a rich and flexible
database communication library, which now provides ways to simplify and
improve on this approach, but there is still a fair degree of tedium involved.
People who work with data a great deal need more power, some way of
moving the queries out of the code, and making them act more like wellbehaved
components in an object-oriented world.Such capabilities have been part of my own (even more) lightweight
object/relational layer for years. It began with a Java database connection
and query pooling system written by my colleague Eric Knapp for
the Lands' End e-commerce site. Our pooler introduced the idea of external
SQL templates that could be accessed by name and efficiently combined
with runtime data to generate the actual database queries. Only later did it grow to include the ability to bind these templates directly to
Java objects, by adding simple mapping directives to the templates.Although far less powerful than a system like Hibernate, this approach
proved valuable in many projects of different sizes and in widely differing
environments. I've continued to use it to this day, most recently in
building IP telephony applications for Cisco's CallManager platform. But
I'm going to be using Hibernate instead from now on. Once you work
through this book, you'll understand why, and will probably make the
same decision yourself. Hibernate does a tremendous amount for you,
and does it so easily that you can almost forget you're working with a
database. Your objects are simply there when you need them. This is
how technology should work.You may wonder how Hibernate relates to Enterprise JavaBeans
TM
. Is it a
competing solution? When would you use one over the other? In fact,
you can use both. Most applications have no need for the complexity of
EJBs, and they can simply use Hibernate directly to interact with a database.
On the other hand, EJBs are indispensable for very complex threetier
application environments. In such cases, Hibernate may be used by
an EJB Session bean to persist data, or it might be used to persist BMP
entity beans. |
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