Building a REST API with Spring Boot

What will you build?

You'll be building a simple Family Cash Card application — a modern way for parents to manage allowance funds for their kiddos. Parents often find themselves lacking an easy way to manage (i.e. send, receive, track) allowances for their kids. So instead of handing out a stack of bills, our cloud-based Family Cash Card app allows parents to virtually manage "cash cards" for their kiddos. You can think of the cash card being very similar to a gift card that many of us send and receive. The primary goal of the Family Cash Card app is to give parents ease and control over managing funds for their children. You'll use Spring Boot to progress from creating a single cash card in a database to allowing for the editing, deleting, and viewing of multiple cash cards, and finally securing your app against unauthorized access and unwanted exploits.

Lab01: Spring Initializr

Spring and Spring Boot are Java frameworks for building applications. Spring is versatile with many modules, while Spring Boot is a streamlined version with pre-configured settings and dependencies. Spring Boot uses Spring Core's Inversion of Control container and Spring Initializr is a tool for generating ready-to-run Spring Boot applications.

Lab02: Testing First

API contracts are formal agreements between API providers and consumers that define how they will interact, what data will be exchanged, and how success and failure cases will be communicated. API contracts are important because they communicate the behavior of a REST API and can be easily translated into functionality and automated tests. JSON is a popular data interchange format for APIs because it is easy to read and write, takes up less space than XML, and works seamlessly with Javascript-based applications.

Test Driven Development (TDD) is an approach where tests are written before implementing application code. This ensures that the system is designed based on desired behavior instead of existing functionality. TDD also guides developers to write the minimum code needed to satisfy the implementation and guards against introducing errors in the future. The Testing Pyramid is a hierarchy of different types of tests, including unit tests, integration tests, and end-to-end tests. The Red, Green, Refactor loop is a development cycle that involves writing a failing test, implementing the simplest thing to make the test pass, and then refactoring the code to improve it without changing any behavior.

Lab03: Implementing GET

REST is a way to manage the values of things via an API, often stored in a database. CRUD are the four basic operations that can be performed on objects in a data store. HTTP is commonly used with REST to handle requests and responses. For each CRUD operation, there is a specific HTTP method to be used: POST for CREATE, GET for READ, PUT for UPDATE, DELETE for DELETE. The endpoint URI for Cash Card objects begins with the /cashcards keyword, and READ, UPDATE, and DELETE require a unique identifier. For CREATE, the application will create a new unique identifier.

Operation	API Endpoint/URI	HTTP Method/Verb	Response StatusCode
Create	/cashcards	POST	201 (CREATED)
Read	/cashcards/{id}	GET	200 (OK)
Update	/cashcards/{id}	PUT	204 (NO DATA)
Delete	/cashcards/{id}	DELETE	204 (NO DATA)

For example,

Request:
  Method: GET
  URL: http://cashcard.example.com/cashcards/123
  Body: (empty)

Response:
  Status Code: 200
  Body:
  {
    "id": 123,
    "amount": 25.00
  }

In Spring Boot, REST is implemented using Spring's IoC container(as opposed to using the Java new keyword) and web controllers.

• Controllers handle requests, and RestController is used to create REST controllers. Controller methods are designated as handler methods using annotations like @GetMapping. The @PathVariable annotation is used to get the value of the requested parameter.
• ResponseEntity is used to produce Response Entities with the correct response code and body.

Lab04: Repositories & Spring Data

The Separation of Concerns principle states that software should be modular with distinct and separate concerns. To enforce data management separation, the Controller-Repository Architecture pattern is used, with the Controller layer near the client and the Repository layer near the data store. Spring Data provides robust data management tools, including implementations of the Repository pattern. An in-memory database, H2, is used for convenience in local development, but trade-offs exist compared to a persistent database. Spring Boot's Auto Configuration feature automatically configures the application to communicate with H2. The CrudRepository, a specific type of Repository in Spring Data, provides convenient out-of-the-box methods for CRUD operations, with implementations generated by Spring Data during IoC container startup time. <<<<<<< Updated upstream

Lab05: Implementing POST

In a REST API, an idempotent operation is one that even if it were to be performed several times, the resulting data on the server would be the same as if it had been performed only once. For each method, the HTTP standard specifies whether it is idempotent or not. GET, PUT, and DELETE are idempotent, whereas POST and PATCH are not.

For example,

Request:
  Method: POST
  URL: http://cashcard.example.com/cashcards/
  Body:
  {
    amount: 123.45
  }

Response:
  Status Code: 201 CREATED
  Header: Location=/cashcards/42