Integrate H2 database with SpringBoot & Spring JPA in Embedded mode

H2 database is a pure Java, open source and very fast engine. We can use H2 for development, testing and performance benchmarking. So in the tutorial, JavaSampleApproach will show how to integrate H2 database with SpringBoot and Spring JPA in Embedded mode.

I. H2 database and SpringBoot integration

H2 database has small footprint (smaller than 1.5 MB) with low memory requirements. It supports for multiple schemas and standard SQL, JDBC API. We can use H2 with disk based or in-memory databases.

H2 can be built by following mode:
– Embedded mode (local connections)
– Server mode (remote connections)
– Mixed mode (local and remote connections)

In the tutorial, We focus on Embedded mode to integrate H2 database and SpringBoot Application.

With Embedded Mode, an application uses JDBC to create a H2 database within the same JVM so it’s very fast to exchange data.

How to configure it with SpringBoot?
-> Spring Boot has a built in H2 database, so We just add below dependency:

    com.h2database
    h2

H2 supports a convenient web based data console to interact with database while the development:

II. Practice

In the tutorial, We create a Spring JPA Web application which uses Spring JPA to interact with H2 database in Embedded mode.

Step to do:
– Create SpringBoot project
– Configure H2 database
– Implement Spring JPA Web Application
– Run & check results

1. Create SpringBoot project

– Using SpringToolSuite, create a SpringBoot project. Then add list dependencies {web, jpa, h2}:

...


	org.springframework.boot
	spring-boot-starter-web


	org.springframework.boot
	spring-boot-starter-data-jpa



    com.h2database
    h2


...

2. Configure H2 database

Open application.properties file, add configurations:

spring.h2.console.enabled=true
spring.h2.console.path=/h2_console
spring.datasource.url=jdbc:h2:file:~/h2/testdb
spring.datasource.username=sa
spring.datasource.password=
spring.datasource.driverClassName=org.h2.Driver
spring.jpa.hibernate.ddl-auto = update
spring.jpa.show-sql=true

Set spring.h2.console.enabled is true to enable web console of H2 database.
spring.h2.console.path is used to define H2 console’s url.
Default setting values of H2 database:
– username/password: sa/’blank’
– driverClassName: org.h2.Driver
– datasource.url: jdbc:h2:mem:testdb

Important!:
– jdbc:h2:mem is used to define In-memory databases.
– jdbc:h2:file is used to define disk-based databases.

3. Implement Spring JPA Web Application

3.1 Create Customer model

package com.javasampleapproach.h2database.model;

import java.io.Serializable;

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 = "customer")
public class Customer implements Serializable {
 
    private static final long serialVersionUID = -3009157732242241606L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column(name = "firstname")
    private String firstName;
 
    @Column(name = "lastname")
    private String lastName;
 
    protected Customer() {
    }
 
    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
 
    @Override
    public String toString() {
        return String.format("Customer[id=%d, firstName='%s', lastName='%s']", id, firstName, lastName);
    }
}

Annotation @Entity indicates that Customer is an Entity and @Table specifies the primary table (name customer) for the annotated @Entity.

@ID specifies the primary key and @GeneratedValue indicates generation strategy for value of primary key.

@Column: mapped column (in the table) for persistent fields (in Java class).

3.2 Create CustomerRepository

This interface helps us do all CRUD functions for class Customer.

package com.javasampleapproach.h2database.repository;

import java.util.List;

import org.springframework.data.repository.CrudRepository;

import com.javasampleapproach.h2database.model.Customer;

public interface CustomerRepository extends CrudRepository{
    List findByLastName(String lastName);
} 

3.3 Create a WebController

Create 3 @RequestMapping:
– @RequestMapping(“/save”)
– @RequestMapping(“/findall”)
– @RequestMapping(“/findbyid”)

package com.javasampleapproach.h2database.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import com.javasampleapproach.h2database.model.Customer;
import com.javasampleapproach.h2database.repository.CustomerRepository;

@RestController
public class WebController {
    @Autowired
    CustomerRepository repository;
       
    @RequestMapping("/save")
    public String process(){
        repository.save(new Customer("Jack", "Smith"));
        repository.save(new Customer("Adam", "Johnson"));
        repository.save(new Customer("Kim", "Smith"));
        repository.save(new Customer("David", "Williams"));
        repository.save(new Customer("Peter", "Davis"));
        return "Done";
    }
       
       
    @RequestMapping("/findall")
    public String findAll(){
        String result = "";
           
        for(Customer cust : repository.findAll()){
            result += cust.toString() + "
";
        }
           
        return result;
    }
       
    @RequestMapping("/findbyid")
    public String findById(@RequestParam("id") long id){
        String result = "";
        result = repository.findOne(id).toString();
        return result;
    }
       
    @RequestMapping("/findbylastname")
    public String fetchDataByLastName(@RequestParam("lastname") String lastName){
        String result = "";
           
        for(Customer cust: repository.findByLastName(lastName)){
            result += cust.toString() + "
"; 
        }
           
        return result;
    }
}

In the web controller methods which are annotated by @RequestMapping, we have used some methods of autowired repository which are implemented interface CrudRepository:

 S save(S entity); //for @RequestMapping("/save")
T findOne(ID id); //for @RequestMapping("/findbyid")
Iterable findAll(); //for @RequestMapping("/findall")

and the method findByLastName that we create in our interface CustomerRepository.

List findByLastName(String lastName);

4. Run & check results

Build and Run the SpringBoot with commandlines: mvn clean install and mvn spring-boot:run.
Make a request: http://localhost:8080/h2_console

Input login’s info as above image. Then press Connect, and makes a first select for customer table:

Make a request: http://localhost:8080/save

Now again select customer table:

Make a request: http://localhost:8080/findall,

Make a request http://localhost:8080/findbyid?id=5,

Now, do restart the SpringBoot App, then select customer table again:

Why?
-> Because we use Disk-memory database by setting: spring.datasource.url=jdbc:h2:file:~/h2/testdb.

III. Sourcecode

SpringBootH2Integration