MyBank

MyBank is an application for handling transaction log and statistics.

The project is based on a small web-service which is created using following technologies:

• Java 1.8
• Maven
• Spring Boot

Roadmap

Project roadmap

Building the project

Prerequisites

For building and running the application you will need:

• JDK 1.8
• Maven 3

We can build the project using mvn as following:

mvn clean install

Please Note!

One of the tests sleeps for about a minute to test that statistics are relevant upto 60 seconds. So mvn clean install or running the StatisticsControllerTest class can take a minute longer than normal.

Running the application

We can run the application locally using various techniques mentioned below, which will start a webserver (Tomcat) on port 8080 (http://localhost:8080) and serves SwaggerUI where we can inspect and try endpoints.

Run from IDE

We can start the application by executing com.mybank.MybankApplication class from your IDE.

Run from Command line

To run the application from command line use Spring Boot Maven plugin as following:

mvn spring-boot:run

Solution

This section will explain high level solution design for the given case.

DataStructure

• Above sixtySecondStatisticsMetrics is a fixed sized Vector<Statistics>.
• It can hold upto Maximum 60 elements.
• Each index in Metrics represent each Second in past one minute.
• Element at each index represents the Statistics of all transactions happened in that indexed second.

Please note again the last point that this structure DOES NOT contain any transaction data.

Operational details/cost on Statistics Metrics

This section will explain how we perform various operations on statisticsMetrics.

Get Statistics

Get Statistics is needed for our /statistics endpoint where user wants to get statistics of transactions happened in last 60 seconds.

• since each index represents the Statistics of transactions happened in that indexed second.
• We need to traverse and accumulate the complete metrics.

Time cost

Since: we loop only for CONSTANT numbers (60) Hence:

O(1)

Space cost

Since: Our Vector at maximum will contain CONSTANT(60) elements Hence:

O(1)

Keep Only 60 seconds Stats and discard older

• With every passing second, each statistics in statisticsMetrics gets one second older.
• As we only need Statistics of last 60 seconds
• We need to continuously update statisticsMetrics
• and discard any states for transactions older than 60 seconds
• following diagram shows the high level design of algorithm to maintain this integrity.

Time cost

Since: we loop only for CONSTANT numbers (60) Hence:

O(1)

Space cost

Since: Our operation will create a Vector which at maximum will contain CONSTANT(60) elements Hence:

O(1)

Handle new transaction

• Whenever a transaction is posted on /transaction endpoint
• Following algorithm evaluates it
• if it is older than 60 seconds, we will discard it: meaning that it will have no impact on statistics.
• otherwise we evaluate its age in seconds (which will be our index in vector)
• and update the statistics on given index as per new transaction

Time cost

O(1)

Space cost

O(1)

Acknowledgments

• To my beautiful family who supported me when I was working on this over the weekend.