RunnableWrapper is a really prime RSF OLI, whose entire code looks as follows:

public interface RunnableWrapper {
  public Runnable wrapRunnable(Runnable towrap);
}

A RunnableWrapper is a "machine", which takes in one unit of work (specified by a standard java.lang.Runnable), and spits out another one, wrapped in some extra logic.

This idea will be familiar to aficionados of AOP, since it is really an equivalent (although a massively more "environmentally friendly" equivalent) of an AOP "execute around" advice. In Chapter 6 of the Spring manual, you can see examples of Spring AOP in action, in particular the "MethodInterceptor" type. Since RSF lives in a request-scope IoC world, the need to express arbitrary "kitchen-sink" interception with support for arbitrary parameters is much lower - rather than pass these values into the wrapping bean as arguments, it is far cleaner for it to fetch them itself as request-scope dependencies.

Here is an example illustrating this point from the RSF LogonTest sample:

public class SecurityWrapper implements RunnableWrapper {
  private ViewParameters viewparams;
  private LogonBean logonbean;

  public void setViewParameters(ViewParameters viewparams) {
    this.viewparams = viewparams;
  }

  public void setLogonBean(LogonBean logonbean) {
    this.logonbean = logonbean;
  }

  public Runnable wrapRunnable(final Runnable towrap) {
    return new Runnable() {
      public void run() {
        if (logonbean.name == null
            && !(LogonProducer.VIEW_ID.equals(viewparams.viewID))) {
          throw new SecurityException("Cannot view page " + viewparams.viewID
              + " while not logged on");
        }
        towrap.run();
      }
    };
  }
}

As we can see, all the inner context for the wrapper is injected in via the request-scope dependencies ViewParameters and LogonBean, and we can keep our clean "nullary interface" to the wrapper itself.

Ruby fans will also recognise the towrap.run(); call as the equivalent of a zero-args yield call. What in Java requires a lot of reflective and AOP sweat (although in RSF, a bit less sweat), is simply part of the language in Ruby, with its powerful support for code-block arguments and "continuation" programming style.