ATM Simulation Test

Build status

Exercise

An application that simulates the backend logic of a cash dispensing Automatic Teller Machine (ATM).

Requirements

Click here for reading the instructions and requirements

Application

This application provides a lightweight RESTful API using the Java API for RESTful Web Services (JAX-RS) on top of an embedded Jetty web application.

A deployed version is running and hosted on: http://atm-simulation-exercise.herokuapp.com/

Frameworks

Server:

• Jetty - Servlet Engine and HTTP Server
• Jersey - RESTful Web Services in Java
• FasterXML - Jackson JAX-RS JSON Provider
• Guava Libraries - Set of common libraries for Java

Test:

• TestNG
• AssertJ - Fluent assertions for Java
• Mockito - Mocking framework

Design patterns

The design pattern used as a base for solving the cash dispenser problem was the Chain of Responsibility.

The typical implementation of a Chain of Responsibility for this specific problem (ATM simulation) has a flaw, mainly because it doesn't care if the request will be fully satisfied at the time the last object in the chain handles it.

For example:

Assuming that the ATM has notes of $20 and $50 only (and it has enough money to fulfil the withdraw):

• We want to withdraw $80
• There are two cash dispensers, one for $50 and other for $20 bills.
• The first one will dispense 1 X $50
• The second (and last one) will dispense 1 X $20
• $70 was dispensed so far
• There is no object in the chain to handle the $10 balance left, making this request to fail

It would work if the chain start with the $20 dispenser, but then another problem is introduced, because the small bills will finish a lot faster, creating an additional cost of constantly feeding the ATM.

The proposed solution is still using this design pattern as a base for its implementation, but it will check if the last object in the chain will satisfy the request before it handles the request to the next one: Dispenser.java

Target platforms

• Mac OSX (tested on 10.9 Mavericks)
• Linux (tested with OpenJDK 7)
• Heroku
• Java stand alone application

Minimum requirements

• Java 7
• Maven 3

Running the application locally

Building the application:

$ mvn clean package

Running it:

$ mvn exec:java -Dexec.mainClass="com.github.golimpio.atm.Main"

Alternatively, there is a run script at the project root folder:

$ ./run

You might need to give execution permission to it:

$ chmod +x run

API

The REST API can be accessed from: http://atm-simulation-exercise.herokuapp.com/services

Or from your localhost if you're running the application locally: http://localhost:8080/services

Services

Following the available services:

1. init (initialise the ATM - GET)
2. init/clear (remove all de available money from the ATM - POST)
3. init/add (add money to the ATM - POST)
4. withdraw (allow withdraw money and verify minimum and maximum amounts allowed - GET)
5. withdraw/ (withdraw cash from the ATM - GET)
6. withdraw/minimum (retrieve the minimum withdraw allowed - GET)
7. withdraw/maximum (retrieve the maximum withdraw allowed - GET)
8. monitor/money (retrieve the amount of notes available for withdraw - GET)

Command line interface

The simplest way to access the service API from the command line is via CURL (a command line tool for transferring data with URL syntax).

Note: replace the url from: http://localhost:8080/services/... to: http://atm-simulation-exercise.herokuapp.com/services/... for using the heroku deployment.

Initialise the ATM removing all the available money from it (2)

Request:

curl -X POST -H "Content-Type: application/json" http://atm-simulation-exercise.herokuapp.com/services/init/clear

or

curl -X POST -H "Content-Type: application/json" http://localhost:8080/services/init/clear

The response will be a HTTP status OK if it succeed or other status if it failed.

Add money to the ATM (3)

Request:

curl -X POST -H "Content-Type: application/json" -d $'[ { "note":"TWENTY", "numberOfNotes":150 }, { "note":"FIFTY", "numberOfNotes":40 } ]' http://atm-simulation-exercise.herokuapp.com/services/init/add

or

curl -X POST -H "Content-Type: application/json" -d $'[ { "note":"TWENTY", "numberOfNotes":150 }, { "note":"FIFTY", "numberOfNotes":40 } ]' http://localhost:8080/services/init/add

Allowed notes:

• FIVE
• TEN
• TWENTY
• FIFTY
• HUNDRED

The response will be a HTTP status OK if it succeed or other status if it failed.

Withdraw (5)

curl -X GET -H "Content-Type: text/plain" -d $'90' http://atm-simulation-exercise.herokuapp.com/services/withdraw/

or

curl -X GET -H "Content-Type: text/plain" -d $'90' http://localhost:8080/services/withdraw/

Response:

  [
	{
      "note":"FIFTY",
      "numberOfNotes":1
    },
    {
      "note":"TWENTY",
      "numberOfNotes":2
    }
  ]

Retrieve the minimal allowed withdraw (6)

Request:

curl -X GET -H "Content-Type: application/json" http://atm-simulation-exercise.herokuapp.com/services/withdraw/minimum

or

curl -X GET -H "Content-Type: application/json" http://localhost:8080/services/withdraw/minimum

Response:

{ "value":20 }

Retrieve the maximum allowed withdraw (7)

Request:

curl -X GET -H "Content-Type: application/json" http://atm-simulation-exercise.herokuapp.com/services/withdraw/maximum

or

curl -X GET -H "Content-Type: application/json" http://localhost:8080/services/withdraw/maximum

Response:

{ "value":5000 }

Retrieve the amount of notes available for withdraw (8)

Request:

curl -X GET -H "Content-Type: application/json" http://atm-simulation-exercise.herokuapp.com/services/monitor/money

or

curl -X GET -H "Content-Type: application/json" http://localhost:8080/services/monitor/money

Response:

  [
    {
      "note":"TWENTY",
      "numberOfNotes":150
    },
    {
      "note":"FIFTY",
      "numberOfNotes":40
    }
  ]