Transaction Statistics - N26 Exercise

Restful API for our transactions and statistics

Goal of this project

The goal of our API is to calculate realtime statistic from the last 60 seconds. There will be two APIs, one of them is called every time a transaction is made. It is also the sole input of this rest API. The other one returns the statistic based of the transactions of the last 60 seconds.

Specs

1. POST /transactions

Every Time a new transaction happened, this endpoint will be called

Body:

{
"amount": 12.3,
"timestamp": 1478192204000
}

● amount - transaction amount ● timestamp - transaction time in epoch in millis in UTC time zone (this is not current timestamp)

Returns: Empty body with either 201 or 204. ● 201 - in case of success ● 204 - if transaction is older than 60 seconds

2. GET /statistics

It returns the statistic based on the transactions which happened in the last 60seconds.

{
"sum": 1000,
"avg": 100,
"max": 200,
"min": 50,
"count": 10
}

Where: ● sum is a double specifying the total sum of transaction value in the last 60 seconds ● avg is a double specifying the average amount of transaction value in the last 60seconds ● max is a double specifying single highest transaction value in the last 60 seconds ● min is a double specifying single lowest transaction value in the last 60 seconds ● count is a long specifying the total number of transactions happened in the last 60seconds

Getting Started

Below are the steps to set up the project in local development environment.

Prerequisites

• IDE - Eclipse / IntelliJ

• JDK1.8

• Maven

  And all paths set in environment variables

Importing the project

Please import the java sources [src folder] using maven import from existing sources in the File-> Import options of IDE. Point the import folder to the folder ( TransactionStatistics ) containing the pom.xml

Folder Structure

TransactionStatistics
 
 |--src
 |   |-main
 |   | |-java
 |   |     |-ApplicationClasses.java
 |   |
 |   |-test
 |       |-java
 |	      |-TestClasses.java
 |--pom.xml

Logic of the API

The Main Logic I have used is whenever a transaction comes in check whether it is within last 60 secons if so add it to transactionMaps and RightAway calculate the statistics for the next sixty seconds.

So whenever a /getstatistics is called withinin next sixty seconds it will return whatever stats calculated while addind transactions

Building the Project

*Right click pom.xml and select Run as Maven Build and execute the goals "clean package install" in eclipse

As we are using spring-boot-maven-plugin to package we will get a single stand-alone jar TransactionStatistics-1.0.0-SNAPSHOT.jar in src/target folder

Executing the program

Execute the below command in command prompt

JarPath>java -jar TransactionStatistics-1.0.0-SNAPSHOT.jar

If you are in Windows run or execute batch script startApplication.bat If you are in Unix run or execute shell script startApplication.sh

Authors

• Selvakumar Kamatchinathan

Thanks To

• Java 8 Streams which made the code easy
• N26 Team for Providing the opportunity to code and learn