Installation of Castor-JDO
To get a head start we'll also start by downloading Castor from this address:
http://castor.exolab.org/download.html.
Select the link "The Castor JARs, docs, DTDs, command line
tools and examples". It'll give you the jar-files for both Castor-JDO and
Castor-XML, documentation (including javadoc) and a few examples. Unzip the
files, locate the Castor-JDO jar file (mine is called
castor-0.9.4.3.jar), put it in you classpath, and then compile this
program:
package hansen.playground;
import org.exolab.castor.jdo.*;
public class CreateMedia {
public static void main(String[] args) {
try {
// Define the JDO object
JDO jdo = new JDO("mydb");
jdo.setConfiguration("database.xml");
// Open a connection to the database
Database db = jdo.getDatabase();
// Begin a transaction
db.begin();
Media m = new Media(2,"VHS");
db.create(m);
// Commit the transaction
db.commit();
db.close();
} catch (PersistenceException e) {
e.printStackTrace();
}
}
}
- Listing 2: The first Castor program -
You don't get it shorter than that. Nevertheless it illustrates the basic
layout of a Castor program. The program creates an instance of object
Media, and stores it in a database. The Media class will be shown
below.
Let's look at the program structure:
- The JDO object is the one that creates the connections to the database.
The name "mydb" refers to a database definition found in the configuration
file "database.xml". We'll look into this file in a second.
- Just like we're used to it when using JDBC we need to have a connection to
the database--this is what getDatabase gives us.
- In order for us to query or store data in the database we must work in an
open transaction. We use the begin method to start a transaction.
- To tell Castor that an object should be stored in the database (when we
commit) we must use the create method.
- commit writes data to the database. After commit you may
start a new transaction, or use...
- close to close the database connection.
My error handling is of course only sufficient for a small test program like
this. In a properly designed program you'd have to be able to close connections
and maybe rollback transactions if severe errors occur. The small program above
may actually throw four different exceptions.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
| 
