Csar

The Concern Separation Aspect Registrar (Csar /zɑːr/) provides access to some concern (usually cross-cutting) that may configured globally or locally to some section of the program. Csar acts like a global service locator that provides flexible, transparent local configuration. Like a czar in American politics, Csar governs configuration and access to program concerns.

Quick Start

1. Include Csar Dependency

Include the appropriate Csar dependency from Maven.

pom.xml

<project>
  …
  <dependencies>
    …
    <dependency>
      <groupId>io.csar</groupId>
      <artifactId>csar</artifactId>
      <version>x.x.x</version>
    </dependency>
  </dependencies>
</project>

2. Make a `Concern`

Implement Concern to represent one of your program's concerns for Csar to register.

Environment.java

public class Environment extends Properties implements Concern {
  …

3. Set the Default Concern

Indicate a fallback concern using Csar.setDefaultConcerns(Concern... concerns) to be accessible by default in any context that has no specific concern configured.

MyApp.java

final Environment defaultEnvironment = new Environment();
defaultEnvironment.setProperty("test", "default");
Csar.setDefaultConcerns(defaultEnvironment);

4. Csar Provides a Concern Configuration

Any code at any time may ask Csar for a concern using Csar.getConcern(Class<C> concernType), indicating the desired type of concern.

If you run code in the context of a specially configured concern using Csar.run(Concern concern, Runnable runnable), Csar.getConcern(Class<C> concernType) will return the locally configured concern; otherwise, it will return the default, fallback concern configuration.

MyApp.java

final Environment defaultEnvironment = new Environment();
defaultEnvironment.setProperty("test", "default");
Csar.setDefaultConcerns(defaultEnvironment);
…
System.out.println(env.getProperty("test")); //prints "default"
…
final Environment localEnvironment = new Environment();
localEnvironment.setProperty("test", "local");
Csar.run(localEnvironment, () -> {
  final Environment env = Csar.getConcern(Environment.class);
  System.out.println(env.getProperty("test")); //prints "local"
});

Learn More

You can access an in-depth introduction to Csar.