Kifaru Codes

Overview
System Flow
Spring Boot
Postgres db

In this project I get to build a CRUD system that is a REST API.

The stack used in this project are:

Java : Language
Spring Boot : Java Framework
PostgreSQL : Database

With Spring boot we start by setting up the dependencies from Spring Boot Initializr as shown below

we then download the generated codebase and load it onto our IDE (I use Intellij).

looking at our codebase, we can see the bare-bones Java application, which liiks like the below code-base:

							
package com.example.backendApi;

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

@SpringBootApplication
public class BackendApiApplication {

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

Running the application will then start the tomcat web-server which can be accessed from localhost:8080 as shown below.

Note

You will get an error at the beginning because there is no database connection. To solve this, comment out the springboot data JPA from pom.xml then reload the project (pom.xml > maven > reload project)
On running the server on localhost:8080, you will get an error (Whitelabel Error Page), as there are no REST endpoints created. To create a simple api read

We then create the application structure, which in this case is a student API.

The student shall have the following parameters:

id
name
email
age
dob

Create a student package where we shall put all the code that is student related, ie:

Student Class : our model
StudentController Class : has all the resources for our API
StudentService Class : Business logic of managing the students
StudentRepository Interface : Acesses your database
StudentConfig Class

PostgreSQL DB

To connect to our database, we need to establish a connection between postgres and the the application.

This is done through the spring data jpa, that is loaded into the src/main/resources/application.properties file, which is shown below:

					
spring.datasource.url=jdbc:postgresql://localhost:5432/database
spring.datasource.username=
spring.datasource.password=
spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect
spring.jpa.properties.hibernate.format_sql=true

The above will contain the database configurations that shall allow you to connect to the database

If you had commented out the database dependency from the pom.xml file, then you can un-comment it and reload the project again

Below is a simple boilerplate code for springboot.

				        
@SpringBootApplication
public class BackendApiApplication {

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

Running this will give an error, however to create a simple Rest API, you can add the @RestController annotation, then add a method with a @GetMapping annotation as shown below

				        
@SpringBootApplication
@RestController
public class BackendApiApplication {

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

	// Return a simple string
	@GetMapping("/")
	public String Hello(){
		return "Hello there";
	}

	// return a JSON object
	@GetMapping("/list")
	public List list(){
		return List.of("Hello", "there");
	}
}

Here is the code for the student class

			      	
// This is our model

package com.example.backendApi.student;

import jakarta.persistence.*;

import java.time.LocalDate;
import java.time.Period;


@Entity
@Table
public class Student {
    @Id
    @SequenceGenerator(
            name = "student_sequence",
            sequenceName = "student_sequence",
            allocationSize = 1
    )
    @GeneratedValue(
            strategy = GenerationType.SEQUENCE,
            generator = "student_sequence"
    )
    private Long id;
    private String name;
    private String email;
    private LocalDate dob;
    @Transient // just means that this does not need to be a column in our database
    private Integer age;

    // load constructors, getters & setters (alt + insert)

    // null r constructor
    public Student() {
    }

    public Student(Long id,
                   String name,
                   String email,
                   LocalDate dob
    ) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.dob = dob;
    }

    // constructor w/o id (This is because the db will generate the id for us)

    public Student(String name,
                   String email,
                   LocalDate dob
    ) {
        this.name = name;
        this.email = email;
        this.dob = dob;
    }

    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 LocalDate getDob() {
        return dob;
    }

    public void setDob(LocalDate dob) {
        this.dob = dob;
    }

    public Integer getAge() {
        return Period.between(this.dob, LocalDate.now()).getYears();
    }

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

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", email='" + email + '\'' +
                ", dob=" + dob +
                ", age=" + age +
                '}';
    }
}

Here is the code for the student Controller class

			      	
package com.example.backendApi.student;

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

import java.util.List;

@RestController
@RequestMapping(path = "api/student")
public class StudentController {

    private final StudentService studentService;

    @Autowired
    public StudentController(StudentService studentService) {
        this.studentService = studentService;
    }

    @GetMapping
    public List getStudents() {
        return studentService.getStudents();
    }

    @PostMapping
    public void registerNewStudent(@RequestBody Student student){
        studentService.addNewStudent(student);
    }

    @DeleteMapping(path = "{studentId}")
    public void deleteStudent(@PathVariable("studentId") Long studentId){
        studentService.deleteStudent(studentId);
    }

    @PutMapping(path = "{studentId}")
    public void updateStudent(
            @PathVariable("studentId") Long studentId,
            @RequestParam(required = false) String name,
            @RequestParam(required = false) String email
    ){
        studentService.updateStudent(studentId, name, email);
    }
}

Here is the code for the student Service class

			      	
package com.example.backendApi.student;

import jakarta.transaction.Transactional;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.time.LocalDate;
import java.time.Month;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

@Service
public class StudentService {

    private final StudentRepository studentRepository;

    @Autowired
    public StudentService(StudentRepository studentRepository) {
        this.studentRepository = studentRepository;
    }

    public List getStudents() {
        return studentRepository.findAll();
    }

    public void addNewStudent(Student student) {
        Optional studentOptional = studentRepository.findStudentByEmail(student.getEmail());

        if (studentOptional.isPresent()){
            throw new IllegalStateException("Email Taken");
        }
        System.out.println(student);
        studentRepository.save(student);
    }

    public void deleteStudent(Long studentId) {
        boolean exists = studentRepository.existsById(studentId);
        if (!exists){
            throw new IllegalStateException("Student with Id:" + studentId + " does not exist.");
        }
        studentRepository.deleteById(studentId);
    }

    @Transactional
    public void updateStudent(Long studentId, String name, String email) {
        Student student = studentRepository
                .findById(studentId)
                .orElseThrow(
                        () -> new IllegalStateException(
                                "Student with Id:" + studentId + " does not exist"
                        )
                );

        if (
                name != null &&
                name.length() > 0 &&
                !Objects.equals(student.getName(), name)
        ){
            student.setName(name);
        }

        if (
                email != null &&
                email.length() > 0 &&
                !Objects.equals(student.getEmail(), email)
        ){
            Optional studentOptional = studentRepository.findStudentByEmail(email);
            if (studentOptional.isPresent()){
                throw new IllegalStateException("email taken");
            }
            student.setEmail(email);
        }
    }

//    @Transactional
//    public void updateStudent(Long studentId){
//
//    }
}

Here is the code for the student Repository Interface

			      	
package com.example.backendApi.student;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;

import java.util.Optional;

@Repository
public interface StudentRepository extends JpaRepository {
    @Query("Select s from Student s where s.email = ?1")
    Optional findStudentByEmail(String email);
}

Here is the code for the student Config class

			      	
package com.example.backendApi.student;

import org.springframework.boot.CommandLineRunner;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.time.LocalDate;
import java.time.Month;
import java.util.List;

import static java.time.Month.*;

@Configuration
public class StudentConfig {
   @Bean
    CommandLineRunner commandLineRunner(StudentRepository repository){
        return args -> {
            Student kifaru = new Student(
                    "Kifaru",
                    "kifaru@mail.com",
                    LocalDate.of(1991, JUNE, 17)
            );

            Student edna = new Student(
                    "edna",
                    "edna@mail.com",
                    LocalDate.of(1993, JUNE, 17)
            );

            repository.saveAll(
                    List.of(kifaru, edna)
            );
        };
    }
}

Spring Boot CRUD project

Table of content

Overview

System Flow

Spring Boot

Note

PostgreSQL DB