So how to enable servlet caching?
1. In administrative console go to
Application servers > "Server name" > Container services > Dynamic cache service
and set "Enable service at server startup" to true.
Application servers > "Server name" > Web container and enable servlet caching for this application server
3. Restart the application server
Note:
More RAM-Space is needed to cache the output.
Servlet output will be cached in RAM during first invocation of JSP/Servlet.