Spring Boot CRUD REST API + Spring Data JPA + H2 Database Example

In this tutorial, we will learn how to develop a CRUD RESTFul API using Spring Boot, Spring Data JPA, Maven, and embedded H2 database.

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.
Get source code of this tutorial on my GitHub Repository.

Table of Contents

  1. What we’ll build?
  2. Tools and Technologies Used
  3. Creating and Importing a Project
  4. Packaging Structure
  5. The pom.xml File
  6. Configure H2 Database
  7. Create JPA Entity - Employee.java
  8. Create a Spring Data Repository - EmployeeRepository.java
  9. Create Spring Rest Controller - EmployeeController.java
  10. Exception(Error) Handling for RESTful Services
  11. Running Application
  12. Integration Testing for REST APIs
  13. Testing REST APIs via Postman Client
  14. Source code on GitHub Repository

1. What we'll build

We will build a CRUD RESTFul APIs for a Simple Employee Management System using Spring Boot 2 JPA and H2 database. Following are five REST APIs (Controller handler methods) are created for Employee resource.

2. Tools and Technologies Used

  • Spring Boot - 2.0.4.RELEASE
  • JDK - 1.8 or later
  • Spring Framework - 5.0.8 RELEASE
  • Hibernate - 5.2.17.Final
  • JPA
  • Maven - 3.2+
  • IDE - Eclipse or Spring Tool Suite (STS)
  • H2 Embedded Database

3. Creating and Importing a Project

There are many ways to create a Spring Boot application. You can refer below articles to create a Spring Boot application.
Refer project structure or packaging structure in the next step.

4. Packaging Structure

Following is the packing structure of our Employee Management System -

5. The pom.xml File

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>net.guides.springboot2</groupId>
    <artifactId>springboot2-jpa-crud-example</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>springboot2-jpa-crud-example</name>
    <description>Demo project for Spring Boot</description>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath />
        <!-- lookup parent from repository -->
    </parent>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </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>
            </plugin>
        </plugins>
    </build>
</project>

6. Configure H2 Database

By default, Spring Boot configures the application to connect to an in-memory store with the username sa and an empty password. However, we can change those parameters by adding the following properties to the application.properties file:

spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
By design, the in-memory database is volatile and data will be lost when we restart the application.

We can change that behavior by using file-based storage. To do this we need to update the spring.datasource.url:
spring.datasource.url=jdbc:h2:file:/data/demo
In this example, we will use a default configuration of the H2 database (we don't use the above configuration, the above configuration is just to know more about H2 database configuration with Spring boot).

7. Create JPA Entity - Employee.java

package net.guides.springboot2.springboot2jpacrudexample.model;

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

@Entity
@Table(name = "employees")
public class Employee {

    private long id;
    private String firstName;
    private String lastName;
    private String emailId;

    public Employee() {

    }

    public Employee(String firstName, String lastName, String emailId) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.emailId = emailId;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }

    @Column(name = "first_name", nullable = false)
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    @Column(name = "last_name", nullable = false)
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    @Column(name = "email_address", nullable = false)
    public String getEmailId() {
        return emailId;
    }
    public void setEmailId(String emailId) {
        this.emailId = emailId;
    }
}

8. Create a Spring Data Repository - EmployeeRepository.java

package net.guides.springboot2.springboot2jpacrudexample.repository;

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

import net.guides.springboot2.springboot2jpacrudexample.model.Employee;

@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long>{

}

9. Create Spring Rest Controller - EmployeeController.java

package net.guides.springboot2.springboot2jpacrudexample.controller;

import java.util.HashMap;

import java.util.List;
import java.util.Map;

import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.CrossOrigin;
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 net.guides.springboot2.springboot2jpacrudexample.exception.ResourceNotFoundException;
import net.guides.springboot2.springboot2jpacrudexample.model.Employee;
import net.guides.springboot2.springboot2jpacrudexample.repository.EmployeeRepository;

@RestController
@RequestMapping("/api/v1")
public class EmployeeController {
    @Autowired
    private EmployeeRepository employeeRepository;

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

    @GetMapping("/employees/{id}")
    public ResponseEntity < Employee > getEmployeeById(@PathVariable(value = "id") Long employeeId)
    throws ResourceNotFoundException {
        Employee employee = employeeRepository.findById(employeeId)
            .orElseThrow(() -> new ResourceNotFoundException("Employee not found for this id :: " + employeeId));
        return ResponseEntity.ok().body(employee);
    }

    @PostMapping("/employees")
    public Employee createEmployee(@Valid @RequestBody Employee employee) {
        return employeeRepository.save(employee);
    }

    @PutMapping("/employees/{id}")
    public ResponseEntity < Employee > updateEmployee(@PathVariable(value = "id") Long employeeId,
        @Valid @RequestBody Employee employeeDetails) throws ResourceNotFoundException {
        Employee employee = employeeRepository.findById(employeeId)
            .orElseThrow(() -> new ResourceNotFoundException("Employee not found for this id :: " + employeeId));

        employee.setEmailId(employeeDetails.getEmailId());
        employee.setLastName(employeeDetails.getLastName());
        employee.setFirstName(employeeDetails.getFirstName());
        final Employee updatedEmployee = employeeRepository.save(employee);
        return ResponseEntity.ok(updatedEmployee);
    }

    @DeleteMapping("/employees/{id}")
    public Map < String, Boolean > deleteEmployee(@PathVariable(value = "id") Long employeeId)
    throws ResourceNotFoundException {
        Employee employee = employeeRepository.findById(employeeId)
            .orElseThrow(() -> new ResourceNotFoundException("Employee not found for this id :: " + employeeId));

        employeeRepository.delete(employee);
        Map < String, Boolean > response = new HashMap < > ();
        response.put("deleted", Boolean.TRUE);
        return response;
    }
}

10. Exception(Error) Handling for RESTful Services

Spring Boot provides a good default implementation for exception handling for RESTful Services. Let’s quickly look at the default Exception Handling features provided by Spring Boot.

Resource Not Present

Heres what happens when you fire a request to not resource found: http://localhost:8080/some-dummy-url
{
  "timestamp": 1512713804164,
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/some-dummy-url"
}
That's a cool error response. It contains all the details that are typically needed.

What happens when we throw an Exception?

Let’s see what Spring Boot does when an exception is thrown from a Resource. we can specify the Response Status for a specific exception along with the definition of the Exception of ‘@ResponseStatus’ annotation.
Lets create a ResourceNotFoundException.java class.
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ResponseStatus;

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

    private static final long serialVersionUID = 1L;

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

Customizing Error Response Structure

Default error response provided by Spring Boot contains all the details that are typically needed.
However, you might want to create a framework independent response structure for your organization. In that case, you can define a specific error response structure.
Let’s define a simple error response bean.
import java.util.Date;

public class ErrorDetails {
    private Date timestamp;
    private String message;
    private String details;

    public ErrorDetails(Date timestamp, String message, String details) {
         super();
         this.timestamp = timestamp;
         this.message = message;
         this.details = details;
    }

    public Date getTimestamp() {
         return timestamp;
    }

    public String getMessage() {
         return message;
    }

    public String getDetails() {
         return details;
    }
}
To use ErrorDetails to return the error response, let’s create a GlobalExceptionHandler class annotated with @ControllerAdvice annotation. This class handles exception specific and global exception in a single place.
import java.util.Date;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.context.request.WebRequest;

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<?> resourceNotFoundException(ResourceNotFoundException ex, WebRequest request) {
         ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
         return new ResponseEntity<>(errorDetails, HttpStatus.NOT_FOUND);
    }

    @ExceptionHandler(Exception.class)
    public ResponseEntity<?> globleExcpetionHandler(Exception ex, WebRequest request) {
        ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
        return new ResponseEntity<>(errorDetails, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

11. Running Application

This spring boot application has an entry point Java class called Application.java with the public static void main(String[] args) method, which you can run to start the application.
import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}
@SpringBootApplication is a convenience annotation that adds all of the following:
  • @Configuration tags the class as a source of bean definitions for the application context.
  • @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.
  • Normally you would add @EnableWebMvc for a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the classpath. This flags the application as a web application and activates key behaviors such as setting up a DispatcherServlet.
  • @ComponentScan tells Spring to look for other components, configurations, and services in the hello package, allowing it to find the controllers.
The main() method uses Spring Boot’s SpringApplication.run() method to launch an application.

12. Integration Testing for REST APIs


There is a separate beautiful article for integration testing for REST APIs on:

>> Spring Boot 2 REST APIs Integration Testing

13. Testing REST APIs via Postman Client

1. Create Employee REST API


HTTP Method: POST 
Note that request and response JSON in the above diagram, the response contains database auto generated id.

2. Get Employee by ID REST API

HTTP Method: GET 

3. Get all Employees REST API

HTTP Method: GET 

4. Update Employee REST API

HTTP Method: GET 

5. Delete Employee REST API

HTTP Method: DELETE 



Get source code of this tutorial on my GitHub Repository.

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