Blog

Hey guys in this post, we will learn about creating REST API with Spring Boot, H2 Database, JPA, and Hibernate. We will also perform the basic CRUD (Create, Read, Update, Delete) operations.

Spring framework is one of the most popular frameworks in the entire java ecosystem. More than 90% of java enterprise applications using the Spring framework in their production.

Spring Boot is a tool to create Spring applications with zero configuration. Spring boot is getting popular day by day that is because you can create REST APIs and Microservices in no time.

JPA is a Java Persistence API, is the most popular data accessor API. It is also getting popular day by day. Almost all the spring boot applications using JPA to access the database data access layer. JPA is just a standard/specification and Hibernate is the implementation.

Application features

So as part of this tutorial, we will be creating a Customer Relationship Management (CRM) API, it has the following features –

• Create customer
• Read single customer
• Read all customers
• Update customer
• Delete customer

Let’s see the rest endpoints for the above features –

Watch the video

Development steps

Following are the development steps to create the spring boot REST API.

Create spring boot application

There are different ways to create a spring boot application. You can pick any one of the following ways to create –

>> Create spring boot application using Spring initializer
>> Create spring boot application in Spring tool suite [STS]
>> Create spring boot application in IntelliJ IDEA

Update maven dependencies

Once the project is created open pom.xml and add the following maven dependencies

<?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>2.4.2</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>in.bushansirgur</groupId>
	<artifactId>springboot</artifactId>
	<version>v1</version>
	<name>springboot</name>
	<description>A spring boot jpa h2 demo</description>
	<properties>
		<java.version>1.8</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>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
			<scope>runtime</scope>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</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>

Configure database

As we have added H2database dependency to the pom.xml, so let’s configure the database URL, username, and password. We will also configure hibernate properties for auto-creating the tables based on the entity. Open application.properties and add the following code –

spring.h2.console.enabled=true
 
spring.datasource.url=jdbc:h2:mem:crm
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
 
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.H2Dialect
spring.jpa.hibernate.ddl-auto=update

We have added spring.h2.console.enabled this tells spring to start H2 database administration inside browser, we can access by visiting this url http://localhost:8080/h2-console

The default username for the h2 database is sa and there is no password for the database. Make sure to add the database name as crm

Note: We configure the H2 database with Spring boot to create and use an in-memory database in runtime, generally for unit testing or POC purposes. Remember an in-memory database is created/initialized when an application starts up; and destroyed when the application shuts down.

Create an entity

Create Customer.java class inside the in.bushansirgur.springboot.entity package and add the following fields

package in.bushansirgur.springboot.entity;

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Entity
@Table(name="tbl_customer")
@Setter
@Getter
@ToString
public class Customer {
	
	@Id
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	private Long id;
	
	private String name;
	
	private Long age;
	
	private String location;
	
	@CreationTimestamp
	@Column(name="created_at", nullable=false, updatable=false)
	private Date createdAt;
	
	@UpdateTimestamp
	@Column(name="updated_at")
	private Date updatedAt;
	
}

@Entity annotation must be added to the entity class, it tells that the entity class is mapped to the database table

@Table annotation is added to tell the name of the table to which the class is mapped to.

@Id annotation is added to make the field uniquely identified, its nothing but the primary key

@GeneratedValue annotation is added for auto-generating the primary key




@Column annotation is added to specify the column name. If you don’t provide @Column annotation then the field name will become the column name.

@CreationTimestamp annotation automatically adds the current date-time when a new object is created

@UpdateTimestamp annotation automatically adds the current date-time when an existing object is updated.

@Setter is a Lombok annotation, which will generate the setters. Similarly, @Getter will generate the getters and @ToString will override the toString()

Create JPA repository

Create ICustomerRepo.java interface inside the package in.bushansirgur.springboot.repository and add the following code

package in.bushansirgur.springboot.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import in.bushansirgur.springdatajpa.entity.Customer;

@Repository
public interface ICustomerRepo extends JpaRepository<Customer, Long> {

}

Spring Data JPA comes with several interfaces to access the database, one of the interfaces is JpaRepository, it provides some of the useful methods to perform the database operations such as Create, Read, Update and Delete

Create a controller to handle requests

Create CustomerController.java class inside in.bushansirgur.springboot.controller package and add the following code

package in.bushansirgur.springboot.controller;

import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import in.bushansirgur.springboot.entity.Customer;
import in.bushansirgur.springboot.repository.ICustomerRepo;

@RestController
@RequestMapping("/api")
public class CustomerController {
	
	@Autowired
	ICustomerRepo customerRepo;
	
	@GetMapping("/customers")
	public ResponseEntity<List<Customer>> getAllCustomers() {
		try {
			List<Customer> list = customerRepo.findAll();
			
			if (list.isEmpty() || list.size() == 0) {
				return new ResponseEntity<>(HttpStatus.NO_CONTENT);
			}
			
			return new ResponseEntity<>(list, HttpStatus.OK);
		} catch (Exception e) {
			return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
		}
	}
	
	@GetMapping("/customers/{id}")
	public ResponseEntity<Customer> getCustomer(@PathVariable Long id) {
		Optional<Customer> customer = customerRepo.findById(id);
		
		if (customer.isPresent()) {
			return new ResponseEntity<>(customer.get(), HttpStatus.OK);
		}
		return new ResponseEntity<>(HttpStatus.NOT_FOUND);
	}
	
	@PostMapping("/customers")
	public ResponseEntity<Customer> saveCustomer(@RequestBody Customer customer) {
		try {
			return new ResponseEntity<>(customerRepo.save(customer), HttpStatus.CREATED);
		} catch (Exception e) {
			return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
		}
	}
	
	@PutMapping("/customers")
	public ResponseEntity<Customer> updateCustomer(@RequestBody Customer customer) {
		try {
			return new ResponseEntity<>(customerRepo.save(customer), HttpStatus.OK);
		} catch (Exception e) {
			return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
		}
	}
	
	@DeleteMapping("/customers/{id}")
	public ResponseEntity<HttpStatus> deleteCustomer(@PathVariable Long id) {
		try {
			Optional<Customer> customer = customerRepo.findById(id);
			if (customer.isPresent()) {
				customerRepo.delete(customer.get());
			}
			return new ResponseEntity<>(HttpStatus.NO_CONTENT);
		} catch (Exception e) {
			return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
		}
	}
}

Run the application

Now we have created the REST API for customer relationship management. It’s time to run the application. There are two ways to run the spring boot application

• By executing the maven command from the root of the application

$ mvn spring-boot:run

• By running the java class

Open SpringbootApplication.java class, it has a main() method. Run the file just like running any other java class.

In a few seconds, the application will start running on port 8080 (localhost:8080)

Test the REST API

We cannot test all the rest endpoints inside the browser. Instead, we will use Postman to test all of the rest endpoints.

• POST /api/customers
• GET /api/customers
• GET /api/customers/2
• GET /api/customers/5

• PUT /api/customers
• DELETE /api/customers/2

Let’s verify once in the H2 Database: