Spring Data JPA with PostgreSQL: A Step-by-Step Tutorial

This tutorial will guide you through setting up Spring Data JPA with PostgreSQL in a Spring Boot 3.2 application using a Student entity as an example.

Prerequisites

• JDK 17 or later
• PostgreSQL Database
• Maven or Gradle
• IDE (IntelliJ IDEA, Eclipse, etc.)

Step 1: Set Up PostgreSQL

Before we begin, ensure that you have PostgreSQL installed and running on your machine. You can download it from the official PostgreSQL website.

1.1 Create a Database

Create a database named testdb in PostgreSQL.

sudo -u postgres psql
CREATE DATABASE testdb;
CREATE USER testuser WITH ENCRYPTED PASSWORD 'password';
GRANT ALL PRIVILEGES ON DATABASE testdb TO testuser;

Step 2: Set Up a Spring Boot Project

2.1 Create a New Spring Boot Project

Use Spring Initializr to create a new project with the following dependencies:

• Spring Web
• Spring Data JPA
• PostgreSQL Driver

Download and unzip the project, then open it in your IDE.

2.2 Configure application.properties

Set up the application properties for your project to connect to the PostgreSQL database. This file is located in the src/main/resources directory.

# src/main/resources/application.properties

# PostgreSQL Database configuration
spring.datasource.url=jdbc:postgresql://localhost:5432/testdb
spring.datasource.username=testuser
spring.datasource.password=password
spring.datasource.driver-class-name=org.postgresql.Driver

# JPA configuration
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect

Explanation:

• Configures the connection to the PostgreSQL database.
• Enables SQL logging.
• Sets up JPA to update the database schema automatically.
• Specifies the Hibernate dialect for PostgreSQL.

Step 3: Define the Entity Class

3.1 Create the Student Entity

Create an entity class to represent a student in the database.

package com.example.demo.entity;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
    private int age;

    // Getters and setters
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

Explanation:

• @Entity: Specifies that the class is an entity and is mapped to a database table.
• @Id and @GeneratedValue: Indicates the primary key and its generation strategy.

Step 4: Create the Repository Interface

4.1 Create the StudentRepository

Create a repository interface to perform CRUD operations on the Student entity.

package com.example.demo.repository;

import com.example.demo.entity.Student;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface StudentRepository extends JpaRepository<Student, Long> {
}

Explanation:

• @Repository: Indicates that the interface is a Spring Data repository.
• JpaRepository<Student, Long>: Provides CRUD operations for the Student entity.

Step 5: Create Service and Controller Layers

5.1 Create the StudentService

Create a service class to handle business logic related to students.

package com.example.demo.service;

import com.example.demo.entity.Student;
import com.example.demo.repository.StudentRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

@Service
public class StudentService {

    @Autowired
    private StudentRepository studentRepository;

    public List<Student> getAllStudents() {
        return studentRepository.findAll();
    }

    public Optional<Student> getStudentById(Long id) {
        return studentRepository.findById(id);
    }

    public Student createStudent(Student student) {
        return studentRepository.save(student);
    }

    public void deleteStudent(Long id) {
        studentRepository.deleteById(id);
    }
}

Explanation:

• @Service: Marks the class as a service component in Spring.
• StudentRepository: Injected to interact with the database.

5.2 Create the StudentController

Create a REST controller to expose endpoints for interacting with students.

package com.example.demo.controller;

import com.example.demo.entity.Student;
import com.example.demo.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.Optional;

@RestController
@RequestMapping("/students")
public class StudentController {

    @Autowired
    private StudentService studentService;

    @GetMapping
    public List<Student> getAllStudents() {
        return studentService.getAllStudents();
    }

    @GetMapping("/{id}")
    public Optional<Student> getStudentById(@PathVariable Long id) {
        return studentService.getStudentById(id);
    }

    @PostMapping
    public Student createStudent(@RequestBody Student student) {
        return studentService.createStudent(student);
    }

    @DeleteMapping("/{id}")
    public void deleteStudent(@PathVariable Long id) {
        studentService.deleteStudent(id);
    }
}

Explanation:

• @RestController: Marks the class as a REST controller.
• @RequestMapping("/students"): Maps the controller to /students endpoint.
• @GetMapping, @PostMapping, @DeleteMapping: Maps HTTP GET, POST, and DELETE requests respectively.
• @RequestBody: Binds the HTTP request body to the Student parameter.
• @PathVariable: Binds the URI template variable to the method parameter.

Step 6: Running and Testing the Application

6.1 Run the Application

Run the Spring Boot application using your IDE or the command line:

./mvnw spring-boot:run

6.2 Test the Endpoints

Use a tool like Postman or your browser to test the endpoints.

Create a Student

• URL: http://localhost:8080/students
• Method: POST
• Body:

  {
      "name": "John Doe",
      "email": "john.doe@example.com",
      "age": 20
  }
  

Get All Students

• URL: http://localhost:8080/students
• Method: GET

Get a Student by ID

• URL: http://localhost:8080/students/{id}
• Method: GET

Delete a Student

• URL: http://localhost:8080/students/{id}
• Method: DELETE

Conclusion

In this tutorial, you have learned how to configure and use Spring Data JPA with PostgreSQL in a Spring Boot 3.2 application. We covered:

• Setting up a PostgreSQL database and creating a new database.
• Setting up a Spring Boot project with Spring Data JPA and PostgreSQL.
• Defining an entity class and repository.
• Creating service and controller layers.
• Running and testing the application using REST endpoints.

By following these steps, you can effectively manage and interact with a PostgreSQL database in your Spring Boot applications using Spring Data JPA.