all index.md files renamed to README.md for more compatibility with github

intercepting-filter/README.md

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+---
+layout: pattern
+title: Intercepting Filter
+folder: intercepting-filter
+permalink: /patterns/intercepting-filter/
+categories: Behavioral
+tags:
+ - Java
+ - Difficulty-Intermediate
+---
+
+## Intent
+Provide pluggable filters to conduct necessary pre-processing and
+post-processing to requests from a client to a target
+ 
+![alt text](./etc/intercepting-filter.png "Intercepting Filter")
+ 
+## Applicability
+Use the Intercepting Filter pattern when
+
+* a system uses pre-processing or post-processing requests
+* a system should do the authentication/ authorization/ logging or tracking of request and then pass the requests to corresponding handlers 
+* you want a modular approach to configuring pre-processing and post-processing schemes
+
+## Real world examples
+
+* [Struts 2 - Interceptors](https://struts.apache.org/docs/interceptors.html)
+
+## Credits
+
+* [TutorialsPoint - Intercepting Filter](http://www.tutorialspoint.com/design_pattern/intercepting_filter_pattern.htm)
+* [Presentation Tier Patterns](http://www.javagyan.com/tutorials/corej2eepatterns/presentation-tier-patterns)