I was exploring ways to do simple, plain-old file-based configuration in Java. I looked into Java's built-in Properties
and the Apache Common Configuration library. For the latter, the distilled code is as follows:
Configurations configs = new Configurations();
Configuration config = null;
try
{
config = configs.properties(new File("config.properties"));
}
catch (ConfigurationException cex)
{
}
long loadQPS = config.getInt("loadQPS");
The issue I have with this is that I find myself inserting this in every single class, which is suboptimal for at least two reasons: 1) I'm reading the file once for every class, when I should only read it once. 2) code duplication.
One obvious solution would be to create a Singleton configuration class that I then access from every other class. But surely this is a desired feature in almost every use case, so shouldn't it be included with the configuration library itself (am I missing something)? I also thought of using Spring configuration, which can create a Singleton configuration class for me, but isn't there too much overhead just for file-based configuration? (Spring's strength is in DI, as I understand.)
What's a good solution, or best practice (if there is one)?
EDIT: A simple static solution suggested in the answer:
public class ConfigClass {
static Configuration config;
static {
Configurations configs = new Configurations();
Logger sysLogger = LoggerFactory.getLogger("sysLogger");
try
{
config = configs.properties(new File("config.properties"));
}
catch (ConfigurationException cex)
{
sysLogger.error("Config file read error");
}
}
}
Access in the package by ConfigClass.config
.
So you have a couple options. One simple one would be to store and access the Configuration object statically.
Another one that I like when I want Dependency Injection without Spring, is to structure program in DI friendly way. You can emulate a DI container by transforming your main() function into a "configuration" of your program that ultimately launches it.
Consider a typical multi-tier web application: A DI friendly main() method might look like:
public class AddressBookApp {
public static void main(String[] args) {
Configuration conf = new Configuration(args[0]);
// Creates our Repository, this might do some internal JDBC initialization
AddressBookRepository repo = new AddressBookRepository(conf);
// Pass the Repository to our Service object so that it can persist data
AddressBookService service = new AddressBookService(repo);
// Pass the Service to the web controller so it can invoke business logic
AddressBookController controller = new AddressBookController(conf, service);
// Now launch it!
new WebApp(new Controller[] { controller }).start();
}
}
This main() serves as a central place to "wire up" your application so it's easy to pass your Configuration object to every component that needs it.