Creating a REST Service with Spring Boot

This guide will help you create a simple REST service using Spring Boot.

You will learn

What is a REST Service?
How to bootstrap a Rest Service application with Spring Initializr?
How to create a Get REST Service for retrieving the courses that a student registered for?
How to create a Post REST Service for registering a course for student?
How to execute Rest Services from Postman?

Rest Services in this Guide

In this guide, we will create three services using proper URIs and HTTP methods:

@GetMapping("/students/{studentId}/courses"): You can ask the courses a specific student has registered for using request method Get and example uri /students/Student1/courses.
@GetMapping("/students/{studentId}/courses/{courseId}"): You can ask a specific course for a specific student using request method Get and example uri /students/Student1/courses/Course1.
@PostMapping("/students/{studentId}/courses") : You can register a student for a course by sending a POST request to URI /students/Student1/courses

Tools you will need

Maven 3.0+ is your build tool
Your favorite IDE. We use Eclipse.
JDK 17

Complete Maven Project With Code Examples

Our Github repository has all the code examples - https://github.com/in28minutes/in28minutes.github.io/tree/master/code-zip-files

Rest Services with Unit and Integration Tests
- Website-springbootrestservices-simplerestserviceswithunitandintegrationtests.zip

What is REST?

REST stands for REpresentational State Transfer. REST specifies a set of architectural constraints. Any service which satisfies these constraints is called RESTful Service.

The five important constraints for RESTful Web Service are

Client - Server : There should be a service producer and a service consumer.
The interface (URL) is uniform and exposing resources.
The service is stateless.
The service results should be Cacheable. HTTP cache, for example.
Service should assume a Layered architecture. Client should not assume direct connection to server - it might be getting info from a middle layer - cache.

Richardson Maturity Model

Richardson Maturity Model is used to identify the maturity level of a Restful Web Service. Following are the different levels and their characteristics:

Level 0 : Expose SOAP web services in REST style. Expose action based services (http://server/getPosts, http://server/deletePosts, http://server/doThis, http://server/doThat etc) using REST.
Level 1 : Expose Resources with proper URI’s (using nouns). Ex: http://server/accounts, http://server/accounts/10. However, HTTP Methods are not used.
Level 2 : Resources use proper URI’s + HTTP Methods. For example, to update an account, you do a PUT to . The create an account, you do a POST to . Uri’s look like posts/1/comments/5 and accounts/1/friends/1.
Level 3 : HATEOAS (Hypermedia as the engine of application state). You will tell not only about the information being requested but also about the next possible actions that the service consumer can do. When requesting information about a facebook user, a REST service can return user details along with information about how to get his recent posts, how to get his recent comments and how to retrieve his friend’s list.

Using appropriate Request Methods

Always use HTTP Methods. Best practices with respect to each HTTP method is described below:

GET : Should not update anything. Should be idempotent (same result in multiple calls). Possible Return Codes 200 (OK) + 404 (NOT FOUND) + 400 (BAD REQUEST)
POST : Should create new resource. Ideally return JSON with link to newly created resource. Same return codes as get possible. In addition : Return code 201 (CREATED) is possible.
PUT : Update a known resource. for example: update client details. Possible Return Codes : 200(OK)
DELETE : Used to delete a resource.

Project Structure

Following screenshot shows the structure of the project we will create.

A few details:

StudentController.java - Rest controller exposing all the three service methods discussed above.
Course.java, Student.java, StudentService.java - Business Logic for the application. StudentService exposes a couple of methods we would consume from our Rest Controller.
StudentControllerIT.java - Integration Tests for the Rest Services.
StudentControllerTest.java - Unit Tests for the Rest Services.
StudentServicesApplication.java - Launcher for the Spring Boot Application. To run the application, just launch this file as Java Application.
pom.xml - Contains all the dependencies needed to build this project. We will use Spring Boot Starter Web.

Bootstrapping REST Services with Spring Initializr

Creating a REST service with Spring Initializr is a cake walk. We will use Spring Web MVC as our web framework.

Spring Initializr http://start.spring.io/ is great tool to bootstrap your Spring Boot projects.

As shown in the image above, following steps have to be done

Launch Spring Initializr and choose the following
- Choose com.in28minutes.springboot as Group
- Choose student-services as Artifact
- Choose following dependencies
  - Web
  - Actuator
  - DevTools
Click Generate Project.
Import the project into Eclipse. File -> Import -> Existing Maven Project.
If you want to understand all the files that are part of this project, you can go here.

Implementing Business Service for your Application

All applications need data. Instead of talking to a real database, we will use an ArrayList - kind of an in-memory data store.

A student can take multiple courses. A course has an id, name, description and a list of steps you need to complete to finish the course. A student has an id, name, description and a list of courses he/she is currently registered for. We have StudentService exposing methods to

public List<Student> retrieveAllStudents() - Retrieve details for all students
public Student retrieveStudent(String studentId) - Retrieve a specific student details
public List<Course> retrieveCourses(String studentId) - Retrieve all courses a student is registered for
public Course retrieveCourse(String studentId, String courseId) - Retrieve details of a specific course a student is registered for
public Course addCourse(String studentId, Course course) - Add a course to an existing student

Refer to these files at the bottom of the article for exact implementation of the Service StudentService and the model classes Course and Student.

src/main/java/com/in28minutes/springboot/model/Course.java
src/main/java/com/in28minutes/springboot/model/Student.java
src/main/java/com/in28minutes/springboot/service/StudentService.java

Adding Couple of GET Rest Services

The Rest Service StudentController exposes couple of get services.

@Autowired private StudentService studentService : We are using Spring Autowiring to wire the student service into the StudentController.
@GetMapping("/students/{studentId}/courses"): Exposing a Get Service with studentId as a path variable
@GetMapping("/students/{studentId}/courses/{courseId}"): Exposing a Get Service for retrieving specific course of a student.
@PathVariable String studentId: Value of studentId from the uri will be mapped to this parameter.

package com.in28minutes.springboot.controller;

import com.in28minutes.springboot.model.Course;
import com.in28minutes.springboot.service.StudentService;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class StudentController {
  @Autowired
  private StudentService studentService;

  @GetMapping("/students/{studentId}/courses")
  public List<Course> retrieveCoursesForStudent(
    @PathVariable String studentId
  ) {
    return studentService.retrieveCourses(studentId);
  }

  @GetMapping("/students/{studentId}/courses/{courseId}")
  public Course retrieveDetailsForCourse(
    @PathVariable String studentId,
    @PathVariable String courseId
  ) {
    return studentService.retrieveCourse(studentId, courseId);
  }
}

Executing the Http Get Operation Using Postman

We will access a request to http://localhost:8080/students/Student1/courses/Course1 to test the service. And will receive the following response shown in the below.

{
  "id": "Course1",
  "name": "Spring",
  "description": "10 Steps",
  "steps": ["Learn Maven", "Import Project", "First Example", "Second Example"]
}

Below picture shows how we can execute this Get Service from Postman - my favorite tool to run rest services.

Adding a Http POST Operation Rest Service

A Http POST Operation should return a status of created (201) when the resource creation is successful.

@PostMapping("/students/{studentId}/courses"): Mapping a url for the POST Request @RequestBody Course newCourse: Using Binding to bind the body of the request to Course object. ResponseEntity.created(location).build(): Return a status of created. Also return the location of created resource as a Response Header.

	@PostMapping("/students/{studentId}/courses")
	public ResponseEntity<Void> registerStudentForCourse(
			@PathVariable String studentId, @RequestBody Course newCourse) {

		Course course = studentService.addCourse(studentId, newCourse);

		if (course == null)
			return ResponseEntity.noContent().build();

		URI location = ServletUriComponentsBuilder.fromCurrentRequest().path(
				"/{id}").buildAndExpand(course.getId()).toUri();

		return ResponseEntity.created(location).build();
	}

Executing a Http POST Operation Rest Service

Example request is shown below. It contains all the details to register a course to a student.

{
  "name": "Microservices",
  "description": "10 Steps",
  "steps": [
    "Learn How to Break Things Up",
    "Automate the hell out of everything",
    "Have fun"
  ]
}

Below picture shows how we can execute this Post operation from Postman - my favorite tool to run rest services. Make sure you go to the Body tab and select raw. Select JSON from the dropdown. Copy above request into body.

The URL we use is http://localhost:8080/students/Student1/courses.