Using the templates in this category you can create: filters.

The most significant part of API 2.3 is the addition of filters - objects that can transform a request or modify a response.
Filters are not servlets; they do not actually create a response. They are preprocessors of the request before it reaches a servlet, and/or postprocessors of the response leaving a servlet.
In a sense, filters are a mature version of the old "servlet chaining" concept. A filter can:

You can configure a filter to act on a servlet or group of servlets; that servlet or group can be filtered by zero or more filters. Practical filter ideas include authentication filters, logging and auditing filters, image conversion filters, data compression filters, encryption filters, tokenizing filters, filters that trigger resource access events, XSLT filters that transform XML content, or MIME-type chain filters (just like servlet chaining).