In this tutorial, we will learn how to use JPA @GeneratedValue annotation in the Spring boot application.
The JPA @GeneratedValue annotation is used to specify the generation strategy for the value of the primary key.
The @GeneratedValue annotation specifies that the entity identifier value is automatically generated using an identity column, a database sequence, or a table generator. Hibernate supports the @GeneratedValue mapping even for UUID identifiers.
JPA supports 4 types of primary key generation strategies – AUTO, TABLE, SEQUENCE, or IDENTITY.
The GenerationType.AUTO is the default generation type and lets the persistence provider choose the generation strategy.
@Entity@Table(name = "student")public class Student { @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name = "id", updatable = false, nullable = false) private Long id; @Column(name = "first_name") private String firstName; @Column(name = "last_name") private String lastName; @Column(name = "email") private String email; public Student() { } // getter and setters}
For example, consider we have a Student JPA entity class with GenerationType.IDENTITY as a generation type:
@Entity@Table(name = "student")public class Student { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "id", updatable = false, nullable = false) private Long id; @Column(name = "first_name") private String firstName; @Column(name = "last_name") private String lastName; @Column(name = "email") private String email; public Student() { } // getter and setters}
The GenerationType.SEQUENCE is to generate primary key values and uses a database sequence to generate unique values.
@Entity@Table(name = "student")public class Student { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE) @Column(name = "id", updatable = false, nullable = false) private Long id; @Column(name = "first_name") private String firstName; @Column(name = "last_name") private String lastName; @Column(name = "email") private String email; public Student() { } // getter and setters}
For example, consider we have a Student JPA entity class with GenerationType.TABLE as generation type:
@Entity@Table(name = "student")public class Student { @Id @GeneratedValue(strategy = GenerationType.TABLE) @Column(name = "id", updatable = false, nullable = false) private Long id; @Column(name = "first_name") private String firstName; @Column(name = "last_name") private String lastName; @Column(name = "email") private String email; public Student() { } // getter and setters}
Let’s create a Spring boot project from the scratch and demonstrates the usage of @GeneratedValue annotation.
We will use Spring Data JPA to develop a repository layer and MySQL database at the backend. We will use the Postman client to test the REST APIs.
1. Create a 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 the 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/> </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 the src/main/resources/application.properties file and add the following properties to it:
spring.datasource.url=jdbc:mysql://localhost:3306/ems?useSSL=falsespring.datasource.username=rootspring.datasource.password=Mysql@123spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialectspring.jpa.hibernate.ddl-auto = updateDon’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 the model package, create a class named Employee and add the following content to 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;}Note that we have used JPA @GeneratedValue annotation to specify the generation strategy (IDENTITY) for the value of the primary key.
@Id @GeneratedValue(strategy = GenerationType.IDENTITY) private long id;5. Create Spring Data JPA Repository
No, we gonna create a Spring Data JPA repository to talk with the MySQL database.
Go to the 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> { }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 REST API
Go to the 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; @PostMapping public Employee createEmployee(@RequestBody Employee employee) { return employeeRepository.save(employee); }}We have built Create Employee REST API to insert an employee into the database.
Create Employee REST API:
@PostMapping public Employee createEmployee(@RequestBody Employee employee) { return employeeRepository.save(employee); }8. Running the Application
Let’s deploy our Spring boot application in a servlet container(embedded tomcat).
Two ways we can start the standalone Spring boot application.
9. Test Create Employee REST API using Postman
Let’s use Create Employee REST API to insert an employee into the database and then we use Update Employee REST API to update the existing employee information.