## Reading Materials 1. <a target="_blank" href="https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern"><i class="external alternate icon"></i> https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern</a> (15 minutes reading) ## Practice Materials 1. Use chain of responsibility pattern to create a naive security filter chain that will check the following responsibilities in order: > 1. If any endpoint matches the request > - *False* - return *Not Found* > 2. If the endpoint has any security rules > - *False* - return *Resource* > 3. If the request contains any authorization header > - *False* - return *Unauthorized request* > 4. If the authorization is approved > - *False* - return *Invalid authorization* > 5. return *Resource* ### Components - Handler (Interface for handling requests) - ConcreteHandler (Handle the request it is the responsibility for or forwards it to its successor) - Client (Initiate the request to a ConcreteHandler object on any part of the chain, in this example, it should start from the the first filter) ### Tips - you may create a Helper class to handle some conditional logic ### Solution <a target="_blank" href="https://github.com/zhenyanghua/design-patterns/tree/master/ChainOfResponsibilityPatternExample/src/main/java"><i class="external alternate icon"></i> Naive Security Chain Example</a> ## Questions to discuss 1. What are the common use cases to apply a **Chain of Responsibility**? 2. What features are there in the application when you see that you should apply the **Chain of Responsibility** pattern?