Java Spring Boot REST Server with PostgreSQL

🕓 45 minutes

What you’ll learn#

How to setup your application for :

connecting to the PostgreSQL database
getting data from REST API
providing data to REST API.

In this tutorial, we will create a simple java component with Java Spring Boot scaffolder with a connection to the PostgreSQL database storage. We want to expose a single REST endpoint for getting the basic client data information, creating a microservice CRUD layer above the DB storage.

Project source#

This example project can be cloned from: http://gitlab.factory.codenow-control.codenow.com/public-docs/java-spring-boot-demo/java-spring-boot-rest-server-with-postgresql.git

Prerequisites#

Prepare your local development environment for CodeNOW with Spring Boot.
- Follow the tutorial instructions in the Java Spring Boot Local Development tutorial.
Run PostgreSQL locally.
- You can run PostgreSQL directly or using docker compose.
- The configuration file for docker-compose can be downloaded from the link that can be found in the section Docker compose and third-party tools of the Java Spring Boot Local Development tutorial.
Create a new component
- For details, see the section Prerequisites of the Java Spring Boot Local Development tutorial.

Steps#

Open your IDE, import the created component and start coding:

Add these maven dependencies to your pom.xml file:
<dependency>
<groupId>javax.persistence</groupId>
<artifactId>javax.persistence-api</artifactId>
<version>2.2</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
<version>2.3.3.RELEASE</version>
</dependency>
Define the JPA entity Client. This simple table will store the basic client data:
- Generate getters and setters with your IDE
  package org.example.service.repository.entity;
  
  import java.time.LocalDate;
  
  import javax.persistence.Entity;
  import javax.persistence.GeneratedValue;
  import javax.persistence.Id;
  
  @Entity
  public class Client {
  @Id
  @GeneratedValue
  private Long id;
  
  private String username;
  private String firstname;
  private String surname;
  private LocalDate birthdate;
  }
Create a new ClientRepository, which is a basic CRUD interface for Spring Boot data DB access:
- For more details about Spring Boot @Repository annotation, see: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/stereotype/Repository.html
  package org.example.service.repository;
  
  import org.example.service.repository.entity.Client;
  import org.springframework.data.jpa.repository.JpaRepository;
  import org.springframework.stereotype.Repository;
  
  @Repository
  public interface ClientRepository extends JpaRepository<Client, Long> {
  Client getClientByUsername(String username);
  }
Create a new controller and put all the parts together
- For more details about Spring Boot controllers, see: https://docs.spring.io/spring/docs/3.0.0.M4/reference/html/ch15s03.html
  package org.example.service.controller;
  
  import org.example.service.repository.ClientRepository;
  import org.example.service.repository.entity.Client;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.web.bind.annotation.GetMapping;
  import org.springframework.web.bind.annotation.PathVariable;
  import org.springframework.web.bind.annotation.RequestMapping;
  import org.springframework.web.bind.annotation.RestController;
  import reactor.core.publisher.Flux;
  
  import javax.validation.constraints.NotNull;
  import java.util.List;
  
  @RestController
  @RequestMapping("/db")
  public class ClientDataController {
  
  private final ClientRepository clientRepository;
  
  @Autowired
  public ClientDataController(ClientRepository clientRepository) {
  this.clientRepository = clientRepository;
  }
  
  @GetMapping("/clients")
  public List<Client> listClients() {
  return clientRepository.findAll();
  }
  
  @GetMapping("/clients/{username}")
  public Flux<Client> getClient(@PathVariable @NotNull String username) {
  return Flux.just(clientRepository.getClientByUsername(username));
  }
  }
Next prepare database configuration:
- Go to the PgAdmin console (http://localhost:5050 if using compose-postgre from our Local development manual) and create a new db client-db with the scheme client-data.
- Add maven dependency to your pom.xml:
  <dependency>
  <groupId>org.postgresql</groupId>
  <artifactId>postgresql</artifactId>
  <version>42.2.11</version>
  </dependency>
Now change the configuration in config/application.yaml:
- Fill {db user} and {db password} according to your configuration
- Make sure you follow yaml syntax (especially whitespaces)
  server:
  port: 8080
  spring:
  main:
  banner-mode: off
  zipkin:
  enabled: false
  datasource:
  url: jdbc:postgresql://localhost:5432/client-db?currentSchema=client-data
  username: {db user}
  password: {db password}
  driverClassName: org.postgresql.Driver
  jpa:
  properties:
  hibernate:
  dialect: org.hibernate.dialect.PostgreSQL95Dialect
  management:
  endpoints:
  web:
  exposure:
  include: health, prometheus
Try to build and run the application in your IDE. After startup, you should be able to access your new controller’s swagger: http://localhost:8080/swagger/index.html
- For correct setup, check the Readme.md in the project root or see the tutorial Java Spring Boot Local Development, section Prepare local development IDE

Deploy to CodeNOW#

If your code works in the local development, you are ready to push your changes to GIT and try to build and deploy your new component version to the CodeNOW environment.

Check the Get New PostgreSQL user manual to get CodeNOW managed component properties.
Make sure to change the application.yaml properties from the local to the production setup.
For more information about application deployment, see the Application Deployment and Deployment Monitoring tutorials.

What’s next?#

See our other developer guides: