How to use config properties file throughout the classes?

Question

I need my Java app to read the config properties from a file and use them throughout the classes. I'm thinking of a separate class, that would return a map of property_key:property_value for each of the properties in the file. Then I would read the values from this map in other classes. Maybe there are other, more commonly used options?

My properties file is simple and has about 15 entries.

Answer 1

Just use java.util.Properties to load it. It implements Map already. You can load and get hold of the properties statically. Here's an example assuming that you've a config.properties file in the com.example package:

public final class Config {

    private static final Properties properties = new Properties();

    static {
        try {
            ClassLoader loader = Thread.currentThread().getContextClassLoader();
            properties.load(loader.getResourceAsStream("com/example/config.properties"));
        } catch (IOException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    public static String getSetting(String key) {
        return properties.getProperty(key);
    }

    // ...
}

Which can be used as

String foo = Config.getSetting("foo");
// ...

You could if necessary abstract this implementation away by an interface and get the instance by an abstract factory.