The front end to an Oracle Application Server, the process to which users connect, is a web listener, the Oracle HTTP Server (OHS). This is in fact a distribution of Apache.All Oracle Application Server instances, whether infrastructure or middle tier, come with an Apache web listener. This web listener can optionally be front ended by a Web Cache. As a general rule, the Web Cache is used for middle tier instances but not for infrastructure instances.
Web listener is a process that monitors one or more ports on one or more addresses for incoming URLs from browsers. It parses these URLs into filenames, locates the files on disk, and copies them back to the browser. Oracle did not write its own web listener. Instead, it chose to distribute the Apache web listener.
The term web server is seriously confusing, as it combines the terms web listener and application server. For this reason, try to avoid using the term Apache web server. The
term HTTP server is more acceptable.
Web listener refer to the front-end processes that manage users’ web sessions.Application server refer to the back-end processes that run application software.
The Apache license does not permit distributors to modify Apache itself. But Apache does come with a mechanism whereby its behavior can be modified legally by creating Apache modules. An Apache module is a dynamically linked program that is invoked when appropriate URLs are received by the web listener. The web listener parses the URL and, rather than mapping it onto a file for download to the browser, will dynamically load and link the appropriate module and pass the request through to that module for further processing. The only difference between the Oracle distribution of Apache and other public domain distribution are the modules that Oracle has written.
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