The Dash Framework enables Java components to be developed with clear and documentable external dependencies on configuration, component wiring, and runtime context.

Dash Obtain

DashObtain: Provides lazy, thread-safe acquisition of fields with the @Obtain annotation. Like dependency injection, but more declarative.

Example @Obtain use (without error handling...):

public class Forwarder implements MessageListener {
  @Obtain MessageProducer forwardTo;

  public void onMessage(Message message) {
    forwardTo.send(message);
  }
}

Dash Context

DashContext: Provides 'safe' global variables: a public static @Context field can be exposed in a thread-safe, thread-local, and execution scoped manner.

An example is authenticated User. Contextual and execution scoped access to the current principal user is easy to show:

public class Authentication {
  @Context static Principal principal;
}

public class Forwarder implements MessageListener {
  ...

  public void onMessage(Message message) {
    Processor userDefault = getProcessorFor(Authentication.principal);
    ...
  }
}

The reference to Authentication.principal will occur within the scoped execution of a message handler. Within that scope the principal can be setup and reliably removed like this:

public class PojoMessageDispatcher {

  @WithinContext
  public void dispatchMessage(Message message, MessageListener listener) {
    Authentication principal = lookupPrincipalFromChannel();
    listener.onMessage(message);
  }
}

The @WithinContext will ensure that principal, once set, will be null-ed out after the dispatchMessage method returns.

Implementation Technology

These Dash projects are implemented with Java 5 and AspectJ. They support compile and load-time weaving.