Pr/1235 Review (#1250)

* Add simple implementation for strangler pattern.

* Add strangler pattern in pom.xml.

* change package name

* Revert "change package name"

This reverts commit 430bd9073e.

* Code review for strangler

Delete final of method parameters.
Add final to private members.
Change package name.

* Revert "Code review for strangler"

This reverts commit d506356708.

* Revert "Revert "Code review for strangler""

This reverts commit c8fd65fda7.

* Remove unnecessary files

strangler/README.md

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+---
+layout: pattern
+title: Strangler
+folder: strangler
+permalink: /patterns/strangler/
+categories: Structural
+tags:
+ - Extensibility
+---
+
+## Intent
+Incrementally migrate a legacy system by gradually replacing specific pieces of functionality
+with new applications and services. As features from the legacy system are replaced, the new
+system eventually covers all the old system's features and may has its own new features, then
+strangling the old system and allowing you to decommission it.
+
+## Class diagram
+![alt text](./etc/strangler.png "Strangler")
+
+## Applicability
+This strangler pattern is a safe way to phase one thing out for something better, cheaper, or 
+more expandable. Especially when you want to update legacy system with new techniques and need 
+continuously develop new features at the same time. Note that this pattern indeed need extra effort, 
+so usually use it when the system is not so simple.
+
+## Credits
+
+* [Strangler pattern](https://docs.microsoft.com/en-us/azure/architecture/patterns/strangler#context-and-problem)
+* [Legacy Application Strangulation : Case Studies](https://paulhammant.com/2013/07/14/legacy-application-strangulation-case-studies/)
+
+