Making the configuration available to all classes

Question

I'm writing a small web server, and it takes a configuration file with all sorts of different options: how many threads to run, which class deals which each file extension, which file to display by default and so on and so forth. To represent this, I'm parsing the config file into a Configuration object which contains all these settings, and the main class holds this object.
However, the config data is required on almost every level of the server - classes within classes within classes...

My question is, what is the best practice to use here? Should I give the config as a parameter for many many classes and pass it back and forth? Should I make it a singleton? Is there another solution I don't see?

Answer 1

Use Guice! Guice is a dependency-injection framework which effectively replaces your use of the new keyword. You define your object bindings in a Module like this:

bind(Configuration.class).to(MySpecificConfiguration.class);
bind(WebServer.class).to(MySpecificWebServerImplementation.class);

And then, instead of newing up WebServer directly, you just ask Guice to do it for you:

WebServer ws = Guice.createInjector(yourModule).getInstance(WebServer.class);

Which will magically create MySpecificWebServerImplementation for you. If MySpecificWebServerImplementation is defined as follows:

public class MySpecificWebServerImplementation {
    @Inject 
    public MySpecificWebServerImplementation(Configuration configuration) {
    }
}

Then MySpecificWebServerImplementation will automatically get given the configuration and you don't have to worry about passing it around.