Spring boot + Spring Data JPA + PostgreSQL example

Before starting the example let’s understand what is spring boot, spring data JPA and Postgresql.

What is a Spring boot?

Spring Boot is an open-source Java framework that simplifies the process of creating and deploying standalone, production-grade Spring-based applications. It is built on top of the popular Spring Framework and provides a streamlined development experience by removing the need for boilerplate configuration and infrastructure setup.

What is Spring Data JPA?

Spring Data JPA is a sub-project of the Spring Data framework that provides a convenient way to interact with relational databases using the Java Persistence API (JPA). It aims to simplify database access and reduce boilerplate code by providing a higher-level abstraction for working with databases.

What is PostgreSQL?

PostgreSQL, also known as Postgres, is a powerful open-source object-relational database management system (DBMS). It is widely recognized for its robustness, extensibility, and adherence to SQL standards. PostgreSQL supports a wide range of features and capabilities, making it suitable for various types of applications and workloads.

Technologies used:

Spring Boot
Spring
Hibernate
HikariCP
PostgreSQL driver
Maven
Java

Here’s an example of a Spring Boot application that uses Spring Data JPA with PostgreSQL as the database. This example demonstrates basic CRUD (Create, Read, Update, Delete) operations on a “User” entity.

First, make sure you have the necessary dependencies in your pom.xml file:

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

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

    <!-- PostgreSQL Driver -->
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
    </dependency>
</dependencies>

Next, create the User entity class representing a table in the PostgreSQL database:

import javax.persistence.*;

@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private String email;

    // constructors, getters, and setters
    // or use lombok
}

Next, create the repository interface for the User entity as UserRepository using Spring Data JPA:

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

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

Now, create the REST controller to handle CRUD operations:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/users")
public class UserController {

    @Autowired
    private UserRepository userRepository;

    @GetMapping
    public List<User> getAllUsers() {
        return userRepository.findAll();
    }

    @GetMapping("/{id}")
    public User getUserById(@PathVariable("id") Long id) {
        return userRepository.findById(id)
                .orElseThrow(() -> new IllegalArgumentException("Invalid user Id: " + id));
    }

    @PostMapping
    public User createUser(@RequestBody User user) {
        return userRepository.save(user);
    }

    @PutMapping("/{id}")
    public User updateUser(@PathVariable("id") Long id, @RequestBody User user) {
        user.setId(id);
        return userRepository.save(user);
    }

    @DeleteMapping("/{id}")
    public void deleteUser(@PathVariable("id") Long id) {
        userRepository.deleteById(id);
    }
}

Finally, configure the PostgreSQL database connection in the application.properties or application.yml file:

spring.datasource.url=jdbc:postgresql://localhost:5432/yourdatabasename
spring.datasource.username=yourusername
spring.datasource.password=yourpassword
spring.jpa.hibernate.ddl-auto=update

Make sure to replace yourdatabasename, yourusername, and mypassword with your actual database details.

That’s it! You now have a Spring Boot application using Spring Data JPA with PostgreSQL. You can run this application as a regular Spring Boot application and access the CRUD operations via REST endpoints at http://localhost:8080/users.

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