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Simplify Your Java Configurations
by Keld H. Hansen
There are many ways to configure Java applications: through Java's Properties files, XML files, databases, and even from the command line. Each of these methods has its own advantages—and its drawbacks, but unfortunately they all offer different ways to access the data values Wouldn't it be nice if there was a uniform API for all of these methods? Something like:
String waitTime = config.getString("waitTime");
You'd ask your "configuration object" for the value of a certain configuration parameter, and then you'd have it—without having to bother knowing where the value was stored. It might have originally come from a properties file, but tomorrow you might move it to a database, and you would be able to do so without having to change a single line in your program.
In the Apache Commons project, you can find a rather anonymous package that will help you achieve these features. It's called Commons Configuration. This article provides a short introduction to the package, with several coding examples.
It's Simple to Use
Conceptually, it's simple to obtain a configuration parameter—and also to save it—and therefore, you'd expect a simple API. This is exactly what you get from Commons Configuration. Here's your first program:
package hansen.playground;
import org.apache.commons.configuration.Configuration;
import org.apache.commons.configuration.ConfigurationException;
import org.apache.commons.configuration.PropertiesConfiguration;
public class MyFirstTry {
public static void main(String[] args) throws ConfigurationException {
// Using a properties file
Configuration config = new PropertiesConfiguration
("myfirsttry.properties");
String day = config.getString("day");
System.out.println(day + ", " + dayInt);
}
}
Now, store a file called myfirsttry.properties with this content in your classpath:
day = 13
Run the program and it will print out 13. Very simple. The idea in Commons Configuration is that every configuration parameter source is handled by a class that implements the Configuration interface. Java's Properties files are handled by the PropertiesConfiguration class. But the Configuration interface has many other implementations. Here are some of the more important ones:
- XMLConfiguration: This implementation handles parameters from XML files.
- DatabaseConfiguration: This implementation consists of parameters from a database.
- JNDIConfiguration: This implementation uses a JNDI datasource.
- SystemConfiguration: This implementation obtains system properties, e.g. from the command line.
- ServletContextConfiguration: This implementation receives the
init parameters for the servlet context.
In the rest of this article, you'll find program examples of how to use these classes.
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