The Oracle Application Express architecture requires some form of Web server to proxy requests between a Web browser and the Oracle Application Express engine. So far you had following possibilities:
- Oracle HTTP Server/mod_plsql
- XDB HTTP protocol server/embedded PL/SQL gateway
It's an alternative that is offered for the above two and with APEX 4.0 it will become the first choice.
Below you see a slide of the APEX 4.0 presentation. It explains what happens more graphically.
The main reasons why you want to consider the APEX Listener:
- it supports file system caching
- it makes the printing of pdfs easier as the APEX Listener is build in Java and integrates nicely with FOP.
- support of multiple file upload, the architecture of mod/plsql didn't allow that
- you can add your own plugins to it
- it has a workload capture feature