Spring Data JPA - Find Records From MySQL

Spring Data JPA simplifies database operations in Spring Boot applications by reducing boilerplate code and providing built-in methods for data access. In this article, we will learn how to retrieve records from a MySQL database using the findById() method, which fetches data based on the primary key and returns an Optional for safe null handling.

• findById() is a predefined method of JpaRepository
• No need to write custom SQL queries

Step-by-Step Implementation

Follow these steps to create, configure, and run a Spring Boot application that retrieves records from a MySQL database using findById() method in Spring Data Jpa.

Step 1: Create a Spring Boot Project

Go to Spring Initializr and generate a Spring Boot project with the following dependencies:

• Spring Web
• Spring Data JPA
• MySQL Driver

Step 2: Open project on IDE

Extract the zip file. Now open a suitable IDE and then go to File -> New -> Project from Existing Sources and select pom.xml. Click on import changes on prompt and wait for the project to sync.

Note: Ensure the same JDK version is selected while importing the Maven project. Also, configure the database connection in application.properties before running the application.

Step 3: Add Required Dependencies

Modify the pom.xml file to include the necessary dependencies:

<dependencies>
    <!-- Spring Boot Data JPA -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>

    <!-- Spring Boot Web Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- MySQL Connector -->
    <dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <scope>runtime</scope>
</dependency> 
</dependencies>

Step 4: Configure Database Connection

• All required configurations should be specified in the application.properties file of the Spring project.
• Add the following properties in src/main/resources/application.properties

spring.datasource.url=jdbc:mysql://localhost:3306/userdb
spring.datasource.username=root # replace with your MySQL username
spring.datasource.password=yourpassword # replace with your MySQL password
spring.jpa.hibernate.ddl-auto=update

Project Directory Structure:

Step 5: Create the Entity Class

Create a User entity in src/main/java/com/example/model/User.java:

import jakarta.persistence.*;

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private String name;
    
    // Constructors
    public User() {}
    
    public User(String name) {
        this.name = name;
    }

    // Getters and Setters
    public int getId() { 
        return id; 
        
    }
    public String getName() { 
        return name;
        
    }
    public void setName(String name) { 
        this.name = name; 
        
    }
}

Step 6: Create Repository Interface

Define a repository interface in src/main/java/com/example/repository/UserRepository.java:

import org.springframework.data.jpa.repository.JpaRepository;
import com.example.model.User;

public interface UserRepository extends JpaRepository<User, Integer> {}

Step 7: Implement Service Class

Create a service to interact with the database in src/main/java/com/example/service/UserService.java:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.example.model.User;
import com.example.repository.UserRepository;
import java.util.Optional;

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public Optional<User> findUserById(int id) {
        return userRepository.findById(id);
    }
}

Step 8: Create Controller for API

Implement a controller to handle HTTP requests in src/main/java/com/example/controller/UserController.java:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import com.example.model.User;
import com.example.service.UserService;
import java.util.Optional;

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping("/{id}")
    public Optional<User> getUserById(@PathVariable int id) {
        return userService.findUserById(id);
    }
}

Step 9: Run the Application 

Start the Spring Boot application using:

mvn spring-boot:run

Output:

Once the application is running, test the API using Postman or a browser:

GET http://localhost:8080/users/1 

Expected Output (JSON Response):

{
"id": 1,
"name": "Aayush"
}