N26 Assignment

Build and Run:

Dependencies

• Application uses junit, mockito for testing
• build.gradle takes care of all the dependencies

Build

• Run gradle build to build the project

Run

• Run gradle bootrun
• Above command starts the application on localhost:8080

APIs

• POST /transactions : saves transactions which are not older than 60 seconds for statistics calculation
• GET /statistics : returns statistics for last 60 seconds

Project details:

Flow

POST request on /transactions -> If timestamp on the transaction is not older than 60 seconds, put it into the
    per second bucket for the calculation.
Keep on clearing transactions who's timestamp is older than 60 seconds by an scheduler which runs in background

GET request on /statistics -> return already calculated statistics result in O(1) time

Details

Store per second aggregated statistics in a ConcurrentHashMap. ConcurrentHashMap is used to allow concurrent request handling and manipulation via scheduled job for deleting old transactions. This runs at every second and checks whether there is any statistics present for older time, If there is any such statistics, remove it from the bucket and calculate the final statistics result again. synchronised for result this variable is being updated through save and clear jobs at the same time.