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When CompositeActionMapper#getMapping(HttpServletRequest, ConfigurationManager) or CompositeActionMapper#getUriFromActionMapping(ActionMapping) is invoked, CompositeActionMapper would go through these ActionMappers in sequence starting from ActionMapper identified by struts.mapper.composite.1, followed by
struts.mapper.composite.2 and finally struts.mapper.composite.3 (in this case) until either one of the ActionMapper return a valid result (not null) or it runs out of ActionMapper in which case it will just return null for both CompositeActionMapper#getMapping(HttpServletRequest, ConfigurationManager) and
CompositeActionMapper#getUriFromActionMapping(ActionMapping) methods.
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