Netflix/archaius

Archaius is a configuration library for accessing a mixture of static as well as dynamic configurations as a single configuration unit.

There are two key concepts to note:

• Properties that can be read by your code.
• Configurations that organize properties into objects you can bootstrap your application with.

• Lock-free property reads.
• Dependency Injection (i.e., Guice) friendly so you don't have to rely on static code execution.

• Not backwards compatible with 1.x.
• Clean separation of API and backing configurations (i.e. commons-configuration, typesafe-configuration, etc).
• Minimal external dependencies.
• Improved bootstrapping process that doesn't rely on class loading.

Archaius provides a set of specialized configuration classes that may be combined using com.netflix.archaius.api.config.CompositeConfig into a specific override structure.
Check out com.netflix.archaius.ProxyFactoryTest (under archaius2-core/test/java/) for an example on how to bootstrap a config and access dynamic properties from it.

All com.netflix.archaius.api.Config (under archaius2-api/) derived classes provide access to their underlying configuration via the numerous getString(), getInt(), getBoolean() methods.
In addition to basic primitives and collections Config will allow parsing to any type that has a constructor that takes a single String argument or a static valueOf(String.class) method.

Archaius supports standard variable replacement syntax such as ${other.property.name}.

Archaius has a default built in loader for .properties files but can also be extended with custom property specifications such as HOCON. In addition multiple contextual overrides for a single configuration resource name may be derived using a com.netflix.archaius.api.CascadeStrategy. The strategy may also specify replacements from already loaded configurations (such as System and Environment properties).

One of the core differentiators between Archaius and other configuration libraries is its support for dynamically changing configuration. Traditionally applications require a restart whenever configuration changes. This can result in unnecessary service interruption during minor configuration changes, such as timeout values. Through Archaius, code can have direct access to the most recent configuration without the need to restart. In addition, code can react to configuration changes by registering a change handler.

Dynamic configuration support is split into the configuration loading and property value resolution.

When adding a DynamicConfig derived configuration CompositeConfig will automatically register for configuration change notifications and incorporate new values into the main configuration.
Archaius provides a base PollingDynamicConfig for use with configuration sources that are polled frequently to refresh the entire configuration snapshot. Implement Config directly for fine grained configuration sources, such as ZooKeeper, which support updates at the individual property granularity.

config.addConfig(new PollingDynamicConfig(
            "REMOTE", 
            new URLConfigReader("http://remoteconfigservice/snapshot"), 
            new FixedPollingStrategy(30, TimeUnit.SECONDS)) 

Use the Property API for optimized access to any property that is expected to be updated at runtime. Access to dynamic configuration follows two access patterns. The first (and most common) is to get the most recent value directly from a Property object.
Property optimizes caching of the resolved property value (from the hierarchy) and is much more efficient than calling the Config object for frequently accessed properties.
The second, and more advanced, access pattern is to react to property value changes via a com.netflix.archaius.api.PropertyListener.

To create a fast property factory using any Config as the source

DefaultPropertyFactory factory = DefaultPropertyFactory.from(config);

To create a com.netflix.archaius.api.Property object

Property<Integer> timeout = factory.getProperty("server.timeout").asInteger(DEFAULT_TIMEOUT_VALUE);

To access the cached property value

Thread.sleep(timeout.get());

To react to property change notification

Property<Integer> timeout = factory
    .getProperty("server.timeout")
    .asInteger() 
    .addListener(new PropertyListener<Integer>() {
        public void onChange(Integer value) {
            socket.setReadTimeout(value);
        }
        
        public void onError(Throwable error) {
        }
    });