FindById in JPA Repository Example

by

A findById(findById()) is a query method in JpaRepository(Spring Data JPA). This method is used to get a JPA Entity based on the provided primary key from the database. In this topic, we will learn how to use the findById() method JpaRepository using the Spring Boot Application with Maven, Spring Web, Spring Data JPA, Lombok and H2 database.

findbyid_method

findById() Method

CrudRepository provides this method to fetch an Entity as given by id.

Optional<T> findById(ID id)
  • The parameter id must not be null.
  • It returns the Optional of the entity with the given id 
  • It throws the exception IllegalArgumentException. If the given id is null.

Let’s create a Restful web service Spring Boot Application with two endpoints API to implement the findById() query method in JpaRepository step-by-step.

These are the following steps:

  1. Creating a Spring Boot Starter Project
  2. Keep the IDE ready
  3. Maven Dependency
  4. Defining the configuration
  5. Creating a JPA Entity
  6. Creating a JPA Repository
  7. Creating a Service Interface
  8. Creating a Service class
  9. Creating a Rest Controller class
  10. Run the Spring Application and Check

1. Creating a Spring Boot Starter Project

 We are creating a Spring Boot Application from the web tool Spring Initializr or you can make it from the IDE(STS, VS Code etc.) you are using. 

Add the following dependencies: 

  • Spring Web
  • Spring Data JPA
  • Lombok
  • H2 Database

2. Keep the IDE ready

We are importing this created application into our Eclipse IDE or you can import it into another IDE you use. You can refer to this article to create and set up the Spring Boot Project in Eclipse IDE.

Project Structure 

findbyid_method

3. Maven Dependency

Here is the complete pom.xml file for the Spring Boot Application.
pom.xml

<?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>2.6.3</version>
		<relativePath />
		<!-- lookup parent from repository -->
	</parent>
	<groupId>com.springjava</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>
	<properties>
		<java.version>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.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<optional>true</optional>
		</dependency>
		<dependency></dependency>
		<groupId>com.h2database</groupId>
		<artifactId>h2</artifactId>
		<scope>runtime</scope>
		<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>

4. Defining the configuration

We are configuring the H2 database configuration in the application.properties file.
application.properties

# H2 Database Configuration
spring.datasource.url=jdbc:h2:mem:test
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
spring.h2.console.enabled=true

5. Creating a JPA Entity

We are creating a JPA entity class Employee with these properties(id, firstName, lastName, department and hireDate).
Employee.java

package com.springjava.entity;

import java.time.LocalDate;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import lombok.Data;

@Data

@Entity

public class Employee {

  @Id

  @GeneratedValue(strategy = GenerationType.IDENTITY)

  private Long id;

  private String firstName;

  private String lastName;

  private String department;

  private LocalDate hireDate;

}
  • This @Data annotation is used for a constructor, setter method, getter method, etc.
  • This @Entity annotation is used to create a table through Java code in the database.

6. Creating a JPA Repository

We are creating a JPA Repository to interact with the JPA Entity class
EmplRepository.java

package com.springjava.repository;

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

import com.springjava.entity.Employee;

public interface EmplRepository extends JpaRepository < Employee, Long > {

}

7. Creating a Service Interface

We are creating a Service interface with some method declaration[save(Employee employee) and getById(Long id)]. So the implementation class of this interface overrides these declared methods.
EmployeeService.java

package com.springjava.service;

import com.springjava.entity.Employee;

public interface EmployeeService {

  void save(Employee employee);

  Employee getById(Long id);

}

8. Creating a Service class

We are creating a Service class EmployeeServiceImpl and this class is implementing the EmployeeServic interface. This class is annotated with @Service annotation to act service. 
EmployeeServiceImpl.java

package com.springjava.service;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Service;

import com.springjava.entity.Employee;

import com.springjava.repository.EmplRepository;

@Service

public class EmployeeServiceImpl implements EmployeeService {

  @Autowired

  EmplRepository empRepo;

  @Override

  public void save(Employee employee) {

    empRepo.save(employee);

  }

  @Override

  public Employee getById(Long id) {

    return empRepo.findById(id).get();

  }

}
  • We used @Autowired annotation to inject the EmplRepository in this service class.
  • We used save() and findById() query methods of that JPA Repository.
empRepo.findById(id).get();
  • This returns an employee based on the given id because of the get() method in the above code. 

9. Creating a Rest Controller class

We are creating a RestController class EmployeeController in which all methods are created for API endpoints for handling requests from the clients. 
EmployeeController.Java

package com.springjava.controller;

import java.time.LocalDate;

import java.util.LinkedHashMap;

import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.http.HttpStatus;

import org.springframework.http.ResponseEntity;

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.RequestBody;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

import com.springjava.entity.Employee;

import com.springjava.service.EmployeeService;

@RestController

@RequestMapping("/api/employee")

public class EmployeeController {

  @Autowired

  EmployeeService empService;

  @PostMapping("/save")

  public ResponseEntity < ? > save(@RequestBody Employee employee) {

    Map < String, Object > respEmp = new LinkedHashMap < String, Object > ();

    employee.setHireDate(LocalDate.now());

    empService.save(employee);

    respEmp.put("status", 1);

    respEmp.put("message", "Record is Saved Successfully!");

    return new ResponseEntity < > (respEmp, HttpStatus.CREATED);

  }

  @GetMapping("/find-by-id/{id}")

  public ResponseEntity < ? > getById(@PathVariable Long id) {

    Map < String, Object > respEmp = new LinkedHashMap < String, Object > ();

    Employee emp = empService.getById(id);

    if (emp != null) {

      respEmp.put("status", 1);

      respEmp.put("data", emp);

      return new ResponseEntity < > (respEmp, HttpStatus.OK);

    } else {

      respEmp.clear();

      respEmp.put("status", 0);

      respEmp.put("message", "Data is not found");

      return new ResponseEntity < > (respEmp, HttpStatus.NOT_FOUND);

    }

  }

}
  • This class is annotated with @RestController annotation to make this class act as a Rest Controller for giving responses in JSON form.
  • We used @RequestMapping annotation to define the base URL for the application.
  • We used @PostMapping and @GetMapping annotations to handle HTTP requests from the client.
  • We used ResponseEntity to represent the entire HTTP response.
  • We used @Autowired  annotation to inject EmployeeService into the class.
  • We used @RequestBody annotation to take JSON object in the save() method as the parameter of the Employee class.
  • We used LocalDate.now() for the current date.
  • We have created two restful web services handling methods[save() and getById()].
  • save(): This saves Employee records into the database.
  • getById(): This fetches employee records by passing the Long type primary key value as a parameter.
  • @PathVariable is used to pass data value in the URL to retrieve data as per that value.

10. Run the Spring Boot Application and Check

Right-click this Spring Boot application on the DemoApplication.java, then click Run As and select Java Application. 

Check H2 Database

Check the H2 database console and browse this URL “http://localhost:8080/h2-console”.

findbyid_method

See the below table here:

findbyid_method

Testing API on the Postman

Saving the employee data

POST: http://localhost:8080/api/employee/save

findbyid_method

Check the table:

findbyid_method

Retrieving the user by an enum value

GET: http://localhost:8080/api/employee/find-by-id/1

findbyid_method

After this API hit Spring Data JPA (internally uses Hibernate as a JPA provider) generated SQL statement in the console below here:

Hibernate: 
select employee0_.id as id1_0_0_, 
employee0_.department as departme2_0_0_, 
employee0_.first_name as first_na3_0_0_, 
employee0_.hire_date as hire_dat4_0_0_, 
employee0_.last_name as last_nam5_0_0_ 
from 
employee employee0_ 
where 
employee0_.id=?

Conclusion

In this topic, we learnt how to use the findById() query method of JPA Repository to get records from the database in Spring Boot Restful web services application.

Leave a Comment