Hi ,
If you want your design as below ,then you need request response bean in sender file channel because File is asynchronous .
File(request response bean)-->Java Mapping-->SOAP-->Mapping(d/b Look up)-->File
If you want to go as below ,yes request response bean not required ,based on your requirement and complexity choose the apt one.
File-->Java Mapping (SOAP lookup)-->Graphical Mapping (d/b Look up) -->File
or
File-->Mapping (SOAP Lookup,d/b look up) -->File
Regards
Venkat