Initiates processing of a collection. CollectionReader initializes the CAS with Documents from the Colection. This method starts the processing in another thread and returns immediately. Status of the processing can be obtained by registering a listener with the {@link #addStatusCallbackListener(StatusCallbackListener)} method.
A CPM can only process one collection at a time. If this method is called while a previous processing request has not yet completed, a UIMA_IllegalStateException
will result. To find out whether a CPM is free to begin another processing request, call the {@link #isProcessing()} method.
@param aCollectionReader the CollectionReader
from which to obtain the Entities to be processed
@throws ResourceInitializationException if an error occurs during initialization
@throws org.apache.uima.UIMA_IllegalStateException if this CPM is currently processing