[Spring] Spring Data REST

Spring Data REST

REST CRUD APIs(10)

Spring Data JPA

• Earlier, We saw the magic of Spring Data JPA
• This helped to eliminate boilerplate code

Can this apply to REST APIs?

The Problem

• We saw how to create a REST API for Employee
• Need to create REST API for another entity?
  • Customer, Student, Product, Book..
• Do we have to repeat all of the same code again?

Wish

• Create a REST API for me
• Use my existing JpaRepository (entity,primary key)
• Give me all of the basic REST API CRUD features for free

Spring Data REST - Solution

• Spring Data REST is the solution
• Leverages your existing JpaRepository
• Spring will give you a REST CRUD implementation for FREE
  • Helps to minimize boiler-plate REST code
  • No new coding required

REST API

• Spring Data REST will expose these endpoints for free

HTTP Method		CRUD Action
POST	/employees	Create a new employee
GET	/employees	Read a list of employees
GET	/employees/{employeeId}	Read a single employee
PUT	/employees/{employeeId}	Update an existing employee
DELETE	/employees/{employeeId}	Delete an existing employee

Get these REST endpoints for free

Spring Data REST - How Does It Work?

• Spring Data REST will scan your project for JpaRepository
• Expose REST APIs for each entity type for your JpaRepository

public interface EmployeeRepository extends JpaRepository<Employee, Integer> {

}

REST Endpoints

• By default, Spring Data REST will create endpoints based on entity type
• Simple pluralized form
  • First character of Entity type is lowercase
  • Then just adds an “s” to the entity

public interface EmployeeRepository extends JpaRepository<Employee, Integer>{

}

Development Process

1. Add spring Data REST to your Mavern POM file

   • That’s it
   • Absolutely NO CODING required

Step 1: Add Spring Data REST to POM file

<dependency>
	<groupId>org.springframework.boot</gropId>
	<artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>

Spring Data REST will scan for JPARepository

In A Nutshell

For Spring Data REST, you only need 3 items

1. Your entity : Employee
2. JpaRepository : EmployeeRepository extends JpaRepository (We already have these two)
3. Maven POM dependency for: spring-boot-starter-data-rest (Only item that is new)

Application Architecture

Minimized Boilerplate Code

• Before Spring Data RREST
  • RESST controller
  • employee service
  • service implementation

    about 3 files and a hundred puls lines of code

• After Spring Data REST

  • NO coding required
  • Just give a Maven POM entry
  • Spring Data REST will scan for those repositories
  • Automatically expose those endpoints for free

HATEOAS

• Spring Data REST endpoints are HATEOAS compliant
  • HATEOAS: Hypermedia as the Engine of Application State
• Hypermedia-driven sites provide information to access REST interfaces
  • Think of it as meta-data for REST data
• Spring Data REST response using HATEOAS
• For example REST response from : GET / employees / 3
• Then it’ll return the JSON data as a response
• For a collection, meta-data includes page size, total elements, pages etc
• For example REST response from: GET / employees
• 133pic 07..IFIW

Advanced Features

• Spring Data REST advanced features
  • Pagination, sorting and searching
  • Extending and adding custom queries with JPQL
  • Query Domain Specific Language(Query DSL)