5.4 Middleware filters
There are operations that are common and require a lot of pre or post processing in web handling. Things like authentication, session management, compression, cookie extraction, logging, and so on. It’s common to provide the code dealing with these issues as pluggable components called Intercepting Filters or Middleware. These operations are common to all pages and it’s convenient to centralize them. They also tend to be agnostic of the actual application, therefore offering a huge reuse potential.
Filters are generally not dependent on each other. When they are, it’s important that they are traversed in the proper order.
They act as pre-processing filters of the request and post-processing filters of the response.
Considering that all requests traverse these filters, their performance is of the highest importance.
[FIGURE: put a layered request -> f1 f2 f3 controller -> response -> f3 f2 f1]