Java Spring Boot with PostgreSQL — CRUD API Project: Part 2/2 (Coding)

/ Java, PostgreSQL, Spring Boot
This is a complete tutorial for beginners on how to develop a Java project using Spring Boot, Spring Data JPA, and PostgreSQL from scratch. This tutorial will help you understand basic concepts, configurations, tools required, and coding to execute a simple API application with Create, Read, Update, and Delete functionalities (CRUD operation).

This article can be divided mainly into 2 sections.

  • One, Tools setup
  • Two, Coding + concepts (CRUD), you are here 😊

Continue if you’ve gone through the environment setup and are ready to code. If not, click on the link below 😊

Java Spring Boot with PostgreSQL — CRUD API Project: Part 1/2 (Tools Installation)

1. Open VS Code

2. Edit pom.xml file

Ensure you have the following dependencies in the 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>3.2.0</version>
  <relativePath/> <!-- lookup parent from repository -->
 </parent>
 <groupId>com.example</groupId>
 <artifactId>employer</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <name>employer</name>
 <description>Demo project for Spring Boot</description>
 <properties>
  <java.version>17</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.springframework.boot</groupId>
   <artifactId>spring-boot-devtools</artifactId>
   <scope>runtime</scope>
   <optional>true</optional>
  </dependency>
  <dependency>
   <groupId>org.projectlombok</groupId>
   <artifactId>lombok</artifactId>
   <optional>true</optional>
  </dependency>
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-test</artifactId>
   <scope>test</scope>
  </dependency>
  <dependency>
   <groupId>org.postgresql</groupId>
   <artifactId>postgresql</artifactId>
   <scope>runtime</scope>
  </dependency>
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-jdbc</artifactId>
  </dependency>
 </dependencies>

 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
     <excludes>
      <exclude>
       <groupId>org.projectlombok</groupId>
       <artifactId>lombok</artifactId>
      </exclude>
     </excludes>
    </configuration>
   </plugin>
  </plugins>
 </build>

</project>

3. Edit application.properties file

spring.application.name=employer

spring.datasource.url=jdbc:postgresql://localhost:5432/employer
spring.datasource.username=postgres
spring.datasource.password=postgres
spring.datasource.driver-class-name=org.postgresql.Driver

#jpa vendor adapter configuration
spring.jpa.database-platform=org.hibernate.dialect.PostgreSQLDialect
spring.jpa.generate-ddl=true
spring.jpa.show-sql=true

spring.jpa.hibernate.ddl-auto=update

server.port=8084
  • employer is the name of the database we will be creating in PostgreSQL
  • The server port number is the port address used to trigger the API call

4. Create the green-highlighted folders

5. Create the following files under the DTO folder

EmployerDTO.java

package com.example.employer.DTO;

public class EmployerDTO {
    
    private int employerID;
    private String employerName;
    private String employerEmail;

    public EmployerDTO(int employerID, String employerName, String employerEmail) {
        this.employerID = employerID;
        this.employerName = employerName;
        this.employerEmail = employerEmail;
    }

    public EmployerDTO() {
    }

    public int getEmployerID() {
        return employerID;
    }

    public void setEmployerID(int employerID) {
        this.employerID = employerID;
    }

    public String getEmployerName() {
        return employerName;
    }

    public void setEmployerName(String employerName) {
        this.employerName = employerName;
    }

    public String getEmployerEmail() {
        return employerEmail;
    }

    public void setEmployerEmail(String employerEmail) {
        this.employerEmail = employerEmail;
    }

    @Override
    public String toString() {
        return "{" +
            " employerID='" + getEmployerID() + "'" +
            ", employerName='" + getEmployerName() + "'" +
            ", employerEmail='" + getEmployerEmail() + "'" +
            "}";
    }
}

EmployerSaveDTO.java

package com.example.employer.DTO;

public class EmployerSaveDTO {
    
    private String employerName;
    private String employerEmail;

    public EmployerSaveDTO(String employerName, String employerEmail) {
        this.employerName = employerName;
        this.employerEmail = employerEmail;
    }

    public EmployerSaveDTO() {
    }

    public String getEmployerName() {
        return employerName;
    }

    public void setEmployerName(String employerName) {
        this.employerName = employerName;
    }

    public String getEmployerEmail() {
        return employerEmail;
    }

    public void setEmployerEmail(String employerEmail) {
        this.employerEmail = employerEmail;
    }

    @Override
    public String toString() {
        return "{" +
            " employerName='" + getEmployerName() + "'" +
            ", employerEmail='" + getEmployerEmail() + "'" +
            "}";
    }
}

EmployerUpdateDTO.java

package com.example.employer.DTO;

public class EmployerUpdateDTO {
    
    private int employerID;
    private String employerName;
    private String employerEmail;

    public EmployerUpdateDTO(int employerID, String employerName, String employerEmail) {
        this.employerID = employerID;
        this.employerName = employerName;
        this.employerEmail = employerEmail;
    }

    public EmployerUpdateDTO() {
    }

    public int getEmployerID() {
        return employerID;
    }

    public void setEmployerID(int employerID) {
        this.employerID = employerID;
    }

    public String getEmployerName() {
        return employerName;
    }

    public void setEmployerName(String employerName) {
        this.employerName = employerName;
    }

    public String getEmployerEmail() {
        return employerEmail;
    }

    public void setEmployerEmail(String employerEmail) {
        this.employerEmail = employerEmail;
    }

    @Override
    public String toString() {
        return "{" +
            " employerID='" + getEmployerID() + "'" +
            ", employerName='" + getEmployerName() + "'" +
            ", employerEmail='" + getEmployerEmail() + "'" +
            "}";
    }
}

6. Create the following file under the Entity folder

Employer.java

package com.example.employer.Entity;

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

@Entity
@Table(name = "employer")
public class Employer {
    
    @Id
    @Column(name = "employer_id", length = 10)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int employerID;

    @Column(name = "employer_name", length = 50)
    private String employerName;

    @Column(name = "employer_email", length = 60)
    private String employerEmail;

    public Employer(int employerID, String employerName, String employerEmail){
        this.employerID = employerID;
        this.employerName = employerName;
        this.employerEmail = employerEmail;
    }

    public Employer(String employerName, String employerEmail){
        this.employerName = employerName;
        this.employerEmail = employerEmail;
    }

    public Employer(){
    }

    public int getEmployerID() {
        return employerID;
    }

    public void setEmployerID(int employerID) {
        this.employerID = employerID;
    }

    public String getEmployerName() {
        return employerName;
    }

    public void setEmployerName(String employerName) {
        this.employerName = employerName;
    }

    public String getEmployerEmail() {
        return employerEmail;
    }

    public void setEmployerEmail(String employerEmail) {
        this.employerEmail = employerEmail;
    }

    @Override
    public String toString() {
        return "{" +
            " employerID='" + getEmployerID() + "'" +
            ", employerName='" + getEmployerName() + "'" +
            ", employerEmail='" + getEmployerEmail() + "'" +
            "}";
    }
}

7. Create the following file under the Repo folder

EmployerRepo.java

package com.example.employer.Repo;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.stereotype.Repository;
import com.example.employer.Entity.Employer;

@EnableJpaRepositories
@Repository
public interface EmployerRepo extends JpaRepository<Employer, Integer>{

}

8. Create the following file under the Service folder

EmployerService.java

package com.example.employer.Service;

import java.util.List;
import com.example.employer.DTO.EmployerDTO;
import com.example.employer.DTO.EmployerSaveDTO;
import com.example.employer.DTO.EmployerUpdateDTO;

public interface EmployerService {
    
    List<EmployerDTO> getAllEmployers();

    String addEmployer(EmployerSaveDTO employerSaveDTO);

    String updateEmployer(EmployerUpdateDTO employerUpdateDTO);

    String deleteEmployer(int employerID);
}

9. Create the following file under the ServiceImpl folder

EmployerServiceImpl.java

package com.example.employer.ServiceImpl;

import java.util.ArrayList;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.example.employer.DTO.EmployerDTO;
import com.example.employer.DTO.EmployerSaveDTO;
import com.example.employer.DTO.EmployerUpdateDTO;
import com.example.employer.Entity.Employer;
import com.example.employer.Repo.EmployerRepo;
import com.example.employer.Service.EmployerService;

@Service
public class EmployerServiceImpl implements EmployerService {

    @Autowired
    private EmployerRepo employerRepo;

    @Override
    public List<EmployerDTO> getAllEmployers() {
        List<Employer> employerList = employerRepo.findAll();

        List<EmployerDTO> employerDTOList = new ArrayList<>();
        for(Employer employer : employerList){
            EmployerDTO employerDTO = new EmployerDTO(employer.getEmployerID(), employer.getEmployerName(), employer.getEmployerEmail());
            employerDTOList.add(employerDTO);
        }

        return employerDTOList;
    }

    @Override
    public String addEmployer(EmployerSaveDTO employerSaveDTO) {
        
        Employer employer = new Employer(employerSaveDTO.getEmployerName(), employerSaveDTO.getEmployerEmail());
        employerRepo.save(employer);
        return employer.getEmployerName();
    }

    @Override
    public String updateEmployer(EmployerUpdateDTO employerUpdateDTO) {
        if(employerRepo.existsById(employerUpdateDTO.getEmployerID())){
            Employer employer = employerRepo.getById(employerUpdateDTO.getEmployerID());

            employer.setEmployerName(employerUpdateDTO.getEmployerName());
            employer.setEmployerEmail(employerUpdateDTO.getEmployerEmail());

            employerRepo.save(employer);
            return "Updated Employer ID: " + employerUpdateDTO.getEmployerID();
        }else{
            return "Employer ID not present";
        }
    }

    @Override
    public String deleteEmployer(int employerID) {
        if(employerRepo.existsById(employerID)){
            employerRepo.deleteById(employerID);

            return "Employer ID deleted: " + employerID;
        }else{
            return "Employer ID not present";
        }
    }
}

10. Create the following file under the ServiceImpl folder

EmployerController.java

package com.example.employer.Controller;

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.DeleteMapping;
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.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.example.employer.DTO.EmployerDTO;
import com.example.employer.DTO.EmployerSaveDTO;
import com.example.employer.DTO.EmployerUpdateDTO;
import com.example.employer.Service.EmployerService;

@RestController
@CrossOrigin
@RequestMapping("api/v1/employer")
public class EmployerController {
    
    @Autowired
    private EmployerService employerService;

    @GetMapping(path = "/getAllEmployers")
    public List<EmployerDTO> getAllEmployers(){
        return employerService.getAllEmployers();
    }

    @PostMapping(path = "/add")
    public String addEmployer(@RequestBody EmployerSaveDTO employerSaveDTO){
        return employerService.addEmployer(employerSaveDTO);
    }

    @PutMapping(path = "/update")
    public String updateEmployer(@RequestBody EmployerUpdateDTO employerUpdateDTO){
        return employerService.updateEmployer(employerUpdateDTO);
    }

    @DeleteMapping(path = "/delete/{employerID}")
    public String deleteEmployer(@PathVariable(value = "employerID") int employerID){
        return employerService.deleteEmployer(employerID);
    }
}

11. Edit the EmployerApplication.java file as below

package com.example.employer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class EmployerApplication {

 public static void main(String[] args) {
  SpringApplication.run(EmployerApplication.class, args);
 }
}

12. Final structure

13. Run the following command in Git Bash to create an employer database

CREATE DATABASE employer WITH ENCODING='UTF8';

14. Open DBeaver

Create a New Database Connection
Database Connection Details
employer Database is Created

15. Run the project in VS Code

Click Run in the EmployerApplication.java OR click RUN from the Main Bar Menu

If the Project build is successful and error-free, the server starts smoothly

16. Open Postman

To add a new employer

Authorization — Type → No Auth

Headers — Content-Type → application/json

add API

To list all added employers

Authorization — Type → No Auth

getAllEmployers API

To update an employer’s details

Authorization — Type → No Auth

Headers — Content-Type → application/json

update API

To delete an employer

Authorization — Type → No Auth

delete API

17. Open DBeaver to verify the results

DBeaver view of employer table with values

Thus, we come to an end of CRUD operations using Spring Boot and PostgreSQL😊

Thank you for reading! I hope you’re able to understand and proceed with the development of this explanation and if so, please share to help others too. 😊

Well, there are a lot of areas for improvement in this project and, for any new suggestions or comments, I’m all ears.

Download project from: https://github.com/sharuroy16/employer

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