Javadoc
FilterActions can always be used as last element of a filter-chain.
FilterAction that are designed to
use other filters to calculate their result, must implement this interface. This way the filters can be exchanged
easily if they support the same Input and Output types.
A separate interface is used because the last element in a filterchain would not need a setNext-method
FilterChainElements should never be instantiated directly. A
FilterChainElementFactory should be used
for that purpose.