extensions/servlet/src/com/google/inject/servlet/ServletScopes.java
public static <T> Callable<T> transferRequest(Callable<T> callable) {
    return wrap(callable, transferRequest());
  }
public static <T> Callable<T> transferRequest(Callable<T> callable) {
    return wrap(callable, transferRequest());
  }
Wraps the given callable in a contextual callable that "transfers" the request to another
thread. This acts as a way of transporting request context data from the current thread to a
future thread.

<p>As opposed to {@link #continueRequest}, this method propagates all existing scoped objects.
The primary use case is in server implementations where you can detach the request processing
thread while waiting for data, and reattach to a different thread to finish processing at a
later time.

<p>Because request-scoped objects are not typically thread-safe, the callable returned by this
method must not be run on a different thread until the current request scope has terminated.
The returned callable will block until the current thread has released the request scope.

@param callable code to be executed in another thread, which depends on the request scope.
@return a callable that will invoke the given callable, making the request context available to
it.
@throws OutOfScopeException if this method is called from a non-request thread, or if the
request has completed.
@since 4.0