code: public void addExposedHeader(String header) {
  
  		Constraint.ensureNotEmpty(header, String.format("Invalid header '%s'", header));
  		exposedHeaders.add(header);
  	}
docs: Add a non-simple resource header exposed by the resource. A simple resource header is one of these: Cache-Control, Content-Language,
  Content-Type, Expires, Last-Modified, Pragma
  
  @param header