Create a REST API in Spring Boot under 30 minutes!

What is REST API?

People usually think REST API is technology or a framework, which is wrong.
REST stands for Representation State Transfer which is a way for computers to communicate with each other efficiently.
There are 4 basic HTTP verbs we use in requests to interact with resources in a REST system:
- GET — retrieve a specific resource (by id) or a collection of resources
- POST — add a new resource
- PUT — update a specific resource (by id)
- DELETE — remove a specific resource by id
For a quick demo, open postman or any browser and type this https://api.github.com/users/bharathkalyans or

`https://api.github.com/users/<github-username>`
The above URI is a `GET` request where <github-username> is your unique id.
You will see a JSON response that contains all the details of that user's GitHub details which are public. To access private repository information you have to pass an API authorization token.

REST API is simply beautiful.

Below is the list of items you must need before starting:

IDE (IntelliJ [preferred], Spring STS, Eclipse, etc.)
Browser or PostMan for testing our API.
PostgreSQL or any SQL to fetch the live data from the database.

Let's start building our REST API (MicroService)

Go to https://start.spring.io/ and select the following as shown in the below figure.
You can change the group id, artifact id and even description as well. Add these 4 dependencies and generate the zip.

You can choose MySQL driver if you are working with MySQL.
Unzip and open the project in `IntelliJ` and let the IDE download the required maven dependencies.
After that rename your application.properties to application.yml and paste the code given below.

server:
  error:
    include-message: always
    include-binding-errors: always
  port: 8080
# Change your port if it is already in use.
spring:
  main:
    banner-mode:
  datasource:
    url: jdbc:postgresql://localhost:5432/databasname
    username: postgres
    password:
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true
    properties:
      hibernate:
        dialect: org.hibernate.dialect.PostgreSQLDialect
        format_sql: true

Once you have done this, you can start the server and you must see your console screen something like this. (Make sure you create a database before running the application, else it might throw an error database not found.)

Create a package model and create a class called Author.

package com.bharathkalyans.myrestapi.model;

import jakarta.persistence.*;

@Entity 
public class Author {

    @Id 
    @SequenceGenerator(name = "author_sequence_generator",            sequenceName = "author_sequence_generator", allocationSize = 1)                @GeneratedValue(strategy = GenerationType.IDENTITY) 
    private Long authorId; 
    private String authorName;

    public Author() { }

    public Author(String authorName) { this.authorName = authorName; }

    public Long getAuthorId() { return authorId; }

    public void setAuthorId(Long authorId) { this.authorId = authorId; }

    public String getAuthorName() { return authorName; }

    public void setAuthorName(String authorName) { 
           this.authorName = authorName; 
    } 
}

Annotations do your job of creating tables. This is handled by Spring JPA.
To handle any incoming requests we must annotate a class with `@RestController`.This class is going to handle our incoming requests.

Create a package controller and create a new class AuthorController inside it.

package com.bharathkalyans.myrestapi.controller;

import com.bharathkalyans.myrestapi.model.Author; 
import com.bharathkalyans.myrestapi.service.AuthorService; 
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; 
import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController @RequestMapping("api/v1") 
public class AuthorController {

    @Autowired 
    AuthorService authorService;

    @GetMapping("/persons") 
    public List getAuthors() { 
            return authorService.getAllAutors(); 
    } 
}

@RequestMapping annotation is added to the class to create a URL path for the request.
@Autowired is used for dependency injection. It creates an object whenever it is required and this is handled by the spring.

Create a package service and create an interface AuthorService and annotate it with @Service.


package com.bharathkalyans.myrestapi.service;

import com.bharathkalyans.myrestapi.model.Author;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public interface AuthorService {
    public List<Author> getAllAuthors();

}

Create a package inside a service called impl and create a class called AuthorServiceImpl and implement the AuthorService.

package com.bharathkalyans.myrestapi.service.impl;

import com.bharathkalyans.myrestapi.dao.AuthorRepository; 
import com.bharathkalyans.myrestapi.model.Author; 
import com.bharathkalyans.myrestapi.service.AuthorService; 
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component;

import java.util.List;

@Component 
public class AuthorServiceImpl implements AuthorService{

    @Autowired 
    private AuthorRepository authorRepository;

    @Override 
    public List getAllAuthors() { 
            return authorRepository.findAll(); 
    } 
}

Create a package dao and create an interface AuthorRepository and implement JpaRepository<ModeName, ID DataType>.

package com.bharathkalyans.myrestapi.dao;

import com.bharathkalyans.myrestapi.model.Author; 
import org.springframework.data.jpa.repository.JpaRepository;

public interface AuthorRepository 
            extends JpaRepository<Author, Long> { }

Make sure that the ID data type must match the Model ID.
And that's it, you don't need to create any query to fetch the data from the database.
You can always create your custom query in this interface using @Query Annotation.
After all the packaging structure must look as shown below
Once you are done with this you can start your application and if there are no errors you can fetch the data from the endpoint specified.
I have manually added data to the database.
Visit https://www.mockaroo.com/ for getting dummy data.
Open postman and hit this endpoint: localhost:8080/api/v1/persons

And congrats 👏🏻 🥳 you have created your first REST API.
I only created the READ operation, if you want me to create it for other CRUD[CREATE READ UPDATE DELETE] operations let me know in the comments.

Project Repository Link

Create a REST API in Spring Boot under 30 minutes!

What is REST API?

Let's start building our REST API (MicroService)

Happy Coding 🫡

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