Processing HTTP Requests

The ICM processes HTTP requests and responses. On the basis of the URL and the port, a “local” handler in the ICM is addressed. Sharing out the requests among different handlers increases performance because a user context does not have to be created for each request. The URL prefixes used for the various handlers can be defined in profile parameters. The handlers are called in the order listed below, and they can process the request themselves or forward it to the next handler.

The SAP Web Dispatcher, which also processes HTTP requests, uses the majority of these handlers.

The local handlers (subhandlers) are called in the order described, provided they have been installed. Which subhandler generates the response depends on how the profile parameters for the URL prefix of the request are defined. If a subhandler has created the HTTP response, the following subhandlers are no longer included in the hierarchy. The exception is the logging handler. This carries out the HTTP logging and forwards it to the next subhandler.

1. Logging Handler

   This handler records HTTP requests. Its use is described in Logging in the ICM and Web Dispatcher .

2. Authentication Handler

   The authorization check for the requested page is carried out here.

3. Server Cache Handler

   This handler is used to read from and write to the ICM server cache and works as follows:

   1. Reads the request

   2. If the requested object is in the cache, it delivers the cache entry to the caller.

   3. If it isn't (access error, cache miss), it passes the request to the next handler.

   4. Stores the entry in the cache before sending the HTTP response to the client

4. Admin Handler

   The admin handler processes administration requests.

   More information:

   Processing Administration Requests

   Using the Web Administration Interface

5. Modification Handler

   The modification handler can change the http request (header fields, URL values, and so on).

   More information: Modifications of HTTP Requests

6. File Access Handler

   This handler returns a file from the file system (suitable for static files as well as images and HTML pages). The URL prefixes the static file access is to be carried out for are determined in the i icm/HTTP/file_access_<xx> parameter.

   More information: icm/HTTP/file_access_<xx>

7. Redirect Handler

   This handler simply forwards the HTTP request to another HTTP server (HTTP redirect). The URL prefixes the ICM is to carry out the redirect for are determined in the icm/HTTP/redirect_<xx> parameter.

   More information: icm/HTTP/redirect_<xx>

8. ABAP Handler

   This handler forwards the request to the AS ABAP and waits for a response. A user context is created in the work process only if this handler is being used.

9. Java Handler

   This handler forwards the request to the integrated Application Server Java.