config

A tiny library (just a few hundred LOC) to simplify reading configuration properties from several locations. It tries to be unobtrusive, to work without surprises, and to be thread-safe. This is not a huge "configuration framework", but more or less a wrapper around Java's Properties class that shortens some common tasks and provides what I consider saner default behaviour.

import static net.e175.klaus.config.PropertiesConfigBuilder.*:

Config config = defaultFromClassloader("myapp.properties")
		.overrideFromFilesystem("/etc/myapp.properties")
		.load();


String hostName = config.key("hostName").asString();
double frequency = config.key("frequency").asDouble();

The Config builder handles null values without choking up, so you can safely do this:

Config config = defaultFromClassloader("myapp.properties")
		.overrideFromFilesystem("/etc/myapp/properties")
		.overrideFromFilesystem(System.getProperty("myapp.propertyfile.location"))
		.load();

The load() method will only throw an exception if it cannot load properties from any of the given locations. The config object is immutable: once built, it will not change. If you want to reload properties, you need to explicitly create a new object with the PropertiesConfigBuilder.

The ConfigValue object returned from Config.key() is never null. You can use it to explicitly check if a value was found at all:

String value = config.key("someKey").asString(); // this throws NoSuchElementException if not found

if(!config.key("someKey").exists()) { // this allows you to check first
	System.err.println("no configuration value found for someKey");
}

In addition, you can find out where a value was loaded from (this is also safe for nonexistent values):

System.out.println( config.key("someKey").loadedFrom() );

Differing from the usual (and hopelessly outdated) convention of Latin-1, configuration files are read as UTF-8. Backslash-u encoding is still possible though:

unicodeKey  = \u0440\u0443\u0441\u0441\u043a\u0438\u0439 \u044f\u0437\u044b\u043a
\u0440\u0443\u0441\u0441\u043a\u0438\u0439 = язык

Requirements and Dependencies

• requires Java SE 7
• depends on slf4j API (http://www.slf4j.org/) for logging (only at DEBUG and TRACE level, so it's usually silent)

Licence

• MIT License (http://www.opensource.org/licenses/mit-license.php)