Get int, float, boolean and string from Properties

If you have a class of configuration values, like your Constants class, and you want to load all values from a configuration (properties) file, you can create a little helper class and use reflection:

public class ConfigLoader {
    public static void load(Class<?> configClass, String file) {
        try {
            Properties props = new Properties();
            try (FileInputStream propStream = new FileInputStream(file)) {
                props.load(propStream);
            }
            for (Field field : configClass.getDeclaredFields())
                if (Modifier.isStatic(field.getModifiers()))
                    field.set(null, getValue(props, field.getName(), field.getType()));
        } catch (Exception e) {
            throw new RuntimeException("Error loading configuration: " + e, e);
        }
    }
    private static Object getValue(Properties props, String name, Class<?> type) {
        String value = props.getProperty(name);
        if (value == null)
            throw new IllegalArgumentException("Missing configuration value: " + name);
        if (type == String.class)
            return value;
        if (type == boolean.class)
            return Boolean.parseBoolean(value);
        if (type == int.class)
            return Integer.parseInt(value);
        if (type == float.class)
            return Float.parseFloat(value);
        throw new IllegalArgumentException("Unknown configuration value type: " + type.getName());
    }
}

Then you call it like this:

ConfigLoader.load(Constants.class, "/path/to/constants.properties");

You can extend the code to handle more types. You can also change it to ignore missing properties, instead of failing like it does now, such that assignments in the field declaration will remain unchanged, i.e. be the default.

http://stackoverflow.com/questions/36723839/get-int-float-boolean-and-string-from-properties