In this tutorial, we will build Spring Boot CRUD REST API Project using IntelliJ IDEA as our IDE. We will use the Postman client to test the REST APIs. We will use Spring Data JPA to develop a repository layer and MySQL database at the backend.

1. Create Spring boot application

Spring Boot provides a web tool called Spring Initializer to bootstrap an application quickly. Just go to https://start.spring.io/ and generate a new spring boot project.

Use the below details in the Spring boot creation:

Project Name: springboot-backend

Project Type: Maven

Choose dependencies: Spring Web, Lombok, Spring Data JPA, and MySQL Driver

Package name: net.javaguides.springboot

Packaging: Jar

Download Spring Boot project as a zip file, unzip it, and import it into IntelliJ IDEA.

Here is the pom.xml file for your reference:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.5.5</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>net.javaguides</groupId>
	<artifactId>springboot-backend</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>springboot-backend</name>
	<description>Demo project for Spring Boot REST APIs</description>
	<properties>
		<java.version>11</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<configuration>
					<excludes>
						<exclude>
							<groupId>org.projectlombok</groupId>
							<artifactId>lombok</artifactId>
						</exclude>
					</excludes>
				</configuration>
			</plugin>
		</plugins>
	</build>

</project>

2. Create Project or Packaging Structure

You below screenshot to create a project or packaging structure for your Spring boot project:

3. Configure MySQL Database

Since we’re using MySQL as our database, we need to configure the database URL, username, and password so that Spring can establish a connection with the database on startup. Open src/main/resources/application.properties file and add the following properties to it:

spring.datasource.url=jdbc:mysql://localhost:3306/ems?useSSL=false
spring.datasource.username=root
spring.datasource.password=Mysql@123

spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialect

spring.jpa.hibernate.ddl-auto = update

Don’t forget to change the spring.datasource.username and spring.datasource.password as per your MySQL installation. Also, create a database named ems in MySQL before proceeding to the next section.

You don’t need to create any tables. The tables will automatically be created by Hibernate from the Employee entity that we will define in the next step. This is made possible by the property spring.jpa.hibernate.ddl-auto = update.

4. Create JPA Entity

Go to model package, create a class named Employee and add the following content into it:

package net.javaguides.springboot.model;

import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "employees")
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email_id")
    private String emailId;
}

5. Create Spring Data JPA Repository

No, we gonna create a Spring Data JPA repository to talk with the MySQL database.

Go to repository package, create the following EmployeeRepository interface and add the following content to it:

package net.javaguides.springboot.repository;

import net.javaguides.springboot.model.Employee;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

public interface EmployeeRepository extends JpaRepository<Employee, Long> {
    // all crud database methods
}

6. Create ResourceNotFoundException Custom Exception

Go to an exception package, create a class named ResourceNotFoundException and add the following content to it:

package net.javaguides.springboot.exception;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ResponseStatus;

@ResponseStatus(value = HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException{

    public ResourceNotFoundException(String message){
        super(message);
    }
}

7. Creating Spring Boot CRUD REST APIs

Go to controller package, create a class named EmployeeController and add the following content to it:

package net.javaguides.springboot.controller;

import net.javaguides.springboot.exception.ResourceNotFoundException;
import net.javaguides.springboot.model.Employee;
import net.javaguides.springboot.repository.EmployeeRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@CrossOrigin("*")
@RestController
@RequestMapping("/api/v1/employees")
public class EmployeeController {

    @Autowired
    private EmployeeRepository employeeRepository;

    @GetMapping
    public List<Employee> getAllEmployees(){
        return employeeRepository.findAll();
    }

    // build create employee REST API
    @PostMapping
    public Employee createEmployee(@RequestBody Employee employee) {
        return employeeRepository.save(employee);
    }

    // build get employee by id REST API
    @GetMapping("{id}")
    public ResponseEntity<Employee> getEmployeeById(@PathVariable  long id){
        Employee employee = employeeRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Employee not exist with id:" + id));
        return ResponseEntity.ok(employee);
    }

    // build update employee REST API
    @PutMapping("{id}")
    public ResponseEntity<Employee> updateEmployee(@PathVariable long id,@RequestBody Employee employeeDetails) {
        Employee updateEmployee = employeeRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Employee not exist with id: " + id));

        updateEmployee.setFirstName(employeeDetails.getFirstName());
        updateEmployee.setLastName(employeeDetails.getLastName());
        updateEmployee.setEmailId(employeeDetails.getEmailId());

        employeeRepository.save(updateEmployee);

        return ResponseEntity.ok(updateEmployee);
    }

    // build delete employee REST API
    @DeleteMapping("{id}")
    public ResponseEntity<HttpStatus> deleteEmployee(@PathVariable long id){

        Employee employee = employeeRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Employee not exist with id: " + id));

        employeeRepository.delete(employee);

        return new ResponseEntity<>(HttpStatus.NO_CONTENT);

    }
}

Get All Employees REST API:

    @GetMapping
    public List<Employee> getAllEmployees(){
        return employeeRepository.findAll();
    }

Create Employee REST API:

    // build create employee REST API
    @PostMapping
    public Employee createEmployee(@RequestBody Employee employee) {
        return employeeRepository.save(employee);
    }

Get Employee by Id REST API:

    // build get employee by id REST API
    @GetMapping("{id}")
    public ResponseEntity<Employee> getEmployeeById(@PathVariable  long id){
        Employee employee = employeeRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Employee not exist with id:" + id));
        return ResponseEntity.ok(employee);
    }

Update Employee REST API:

    // build update employee REST API
    @PutMapping("{id}")
    public ResponseEntity<Employee> updateEmployee(@PathVariable long id,@RequestBody Employee employeeDetails) {
        Employee updateEmployee = employeeRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Employee not exist with id: " + id));

        updateEmployee.setFirstName(employeeDetails.getFirstName());
        updateEmployee.setLastName(employeeDetails.getLastName());
        updateEmployee.setEmailId(employeeDetails.getEmailId());

        employeeRepository.save(updateEmployee);

        return ResponseEntity.ok(updateEmployee);
    }

Delete Employee REST API:

    // build delete employee REST API
    @DeleteMapping("{id}")
    public ResponseEntity<HttpStatus> deleteEmployee(@PathVariable long id){

        Employee employee = employeeRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Employee not exist with id: " + id));

        employeeRepository.delete(employee);

        return new ResponseEntity<>(HttpStatus.NO_CONTENT);

    }

8. Running the Application

We have successfully developed all the CRUD Rest APIs for the Employee model. Now it's time to deploy our application in a servlet container(embedded tomcat).

Two ways we can start the standalone Spring boot application.

1. From the root directory of the application and type the following command to run it -

$ mvn spring-boot:run

2. From your IDE, run the SpringbootBackendApplication.main() method as a standalone Java class that will start the embedded Tomcat server on port 8080 and point the browser to http://localhost:8080/.