A request handler is an ABAP Objects class which "handles Requests", web requests that is. SAP uses it to show ABAP statement documentation via a web browser...
The Request handler
A request handler is a class implementation of interface IF_HTTP_EXTENSION such asCL_HTTP_EXT_ITS. It is set up on the HTTP service via transaction SICF – “HTTP Service Hierarchy Maintenance”. A request handler can perform the full cycle of “question – answer” receiving a HTTP request, answering in a HTTP response. E.g. request handler CL_HTTP_EXT_DOCU was set up to respond directly by presenting the requested documentation in a HTML-presentable format. HTTP services can have multiple request handlers which will all be called in predefined sequence (transactionSICF).
The most commonly used request handler in SAP is CL_HTTP_EXT_ITS (as above) which sole task is to find a transaction code to call – and then call it. There’s a variety of ways in which a transaction code can be passed to the CL_HTTP_EXT_ITS request handler, a parameter (~transaction) on the service, the same parameter in the URL or the ~okcode can be interpreted as a transaction code. If you are setting up an internet service based on a screen flow of a transaction, just use theCL_HTTP_EXT_ITS as request handler.