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 Kotlin 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.
How to configure it with SpringBoot?
-> Spring Boot has a built in H2 database, so We just add below dependency:
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>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 Kotlin SpringBoot project
– Configure H2 database
– Implement Kotlin Spring JPA Web Application
– Run & check results
1. Create Kotlin SpringBoot project
Using SpringToolSuite, create a SpringBoot project. Then add list dependencies {web, jpa, h2}:
...
<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>
</dependency>
...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 Kotlin Spring JPA Web Application
3.1 Create Customer model
package com.javasampleapproach.kotlin.h2.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 = "customer")
public class Customer(
@Id
val id: Long = -1,
@Column(name = "firstname")
val firstName: String = "",
@Column(name = "lastname")
val lastName: String = ""
){
override fun toString(): String{
return "Customer[id=${id}, firstName=${firstName}, lastName=${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.kotlin.h2.repository
import org.springframework.data.repository.CrudRepository
import com.javasampleapproach.kotlin.h2.model.Customer
interface CustomerRepository: CrudRepository{
fun findByLastName(lastName: String): List
}
3.3 Create a WebController
Create 3 @RequestMapping:
– @RequestMapping(“/save”)
– @RequestMapping(“/findall”)
– @RequestMapping(“/findbyid”)
package com.javasampleapproach.kotlin.h2.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.kotlin.h2.model.Customer
import com.javasampleapproach.kotlin.h2.repository.CustomerRepository
@RestController
class WebController {
@Autowired
lateinit var repository: CustomerRepository
@RequestMapping("/save")
fun process(): String{
repository.save(Customer(1, "Jack", "Smith"))
repository.save(Customer(2, "Adam", "Johnson"))
repository.save(Customer(3, "Kim", "Smith"))
repository.save(Customer(4, "David", "Williams"))
repository.save(Customer(5, "Peter", "Davis"))
return "Done"
}
@RequestMapping("/findall")
fun findAll(): String{
var result = ""
for(cust in repository.findAll()){
result += cust.toString() + ""
}
return result
}
@RequestMapping("/findbyid")
fun findById(@RequestParam("id") id: Long): String{
return repository.findOne(id).toString()
}
@RequestMapping("/findbylastname")
fun fetchDataByLastName(@RequestParam("lastname") lastName: String): String{
var result = ""
for(cust in 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 extends T> S save(S entity); //for @RequestMapping("/save")
T findOne(ID id); //for @RequestMapping("/findbyid")
Iterable<T> 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.
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