Build Update Student REST API

Introduction

In this chapter, we will build an Update Student REST API for our Student Management System Project with a MySQL database. We will update the service layer, build the Update Student REST API, and test it using the Postman client. Each step will be explained in detail. In the next chapter, we will build a Delete Student REST API.

What We Will Cover in This Chapter

• Update a Service Layer (interface and implementation class)
• Build Update Student REST API
• Test using Postman client
• Conclusion

Update a Service Layer

Update the Service Interface

1. Open StudentService Interface:
   • In the src/main/java/com/example/springbootmysqlcrud/service directory, open the StudentService interface.
   • Add the following method to the StudentService interface:

package com.example.springbootmysqlcrud.service;

import com.example.springbootmysqlcrud.model.Student;
import java.util.List;
import java.util.Optional;

public interface StudentService {
    Student saveStudent(Student student);
    Optional<Student> getStudentById(Long id);
    List<Student> getAllStudents();
    Student updateStudent(Long id, Student student);
}

Explanation

• Service Interface: Defines the contract for the service layer. It now includes the updateStudent method to update a student’s details.

Update the Service Implementation Class

1. Open StudentServiceImpl Class:
   • In the src/main/java/com/example/springbootmysqlcrud/service directory, open the StudentServiceImpl class.
   • Add the following method to the StudentServiceImpl class:

package com.example.springbootmysqlcrud.service;

import com.example.springbootmysqlcrud.model.Student;
import com.example.springbootmysqlcrud.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 StudentServiceImpl implements StudentService {

    @Autowired
    private StudentRepository studentRepository;

    @Override
    public Student saveStudent(Student student) {
        return studentRepository.save(student);
    }

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

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

    @Override
    public Student updateStudent(Long id, Student studentDetails) {
        return studentRepository.findById(id)
                .map(student -> {
                    student.setFirstName(studentDetails.getFirstName());
                    student.setLastName(studentDetails.getLastName());
                    student.setEmail(studentDetails.getEmail());
                    return studentRepository.save(student);
                })
                .orElse(null);
    }
}

Explanation

• updateStudent Method: Implements the updateStudent method defined in the StudentService interface to update a student’s details using the repository.

Build Update Student REST API

Create or Update the Controller Class

1. Open StudentController Class:
   • In the src/main/java/com/example/springbootmysqlcrud/controller directory, open the StudentController class.
   • Add the following method to the StudentController class:

package com.example.springbootmysqlcrud.controller;

import com.example.springbootmysqlcrud.model.Student;
import com.example.springbootmysqlcrud.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

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

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

    @Autowired
    private StudentService studentService;

    @PostMapping
    public ResponseEntity<Student> saveStudent(@RequestBody Student student) {
        Student savedStudent = studentService.saveStudent(student);
        return new ResponseEntity<>(savedStudent, HttpStatus.CREATED);
    }

    @GetMapping("/{id}")
    public ResponseEntity<Student> getStudentById(@PathVariable Long id) {
        Optional<Student> student = studentService.getStudentById(id);
        return student.map(value -> new ResponseEntity<>(value, HttpStatus.OK))
                      .orElseGet(() -> new ResponseEntity<>(HttpStatus.NOT_FOUND));
    }

    @GetMapping
    public ResponseEntity<List<Student>> getAllStudents() {
        List<Student> students = studentService.getAllStudents();
        return new ResponseEntity<>(students, HttpStatus.OK);
    }

    @PutMapping("/{id}")
    public ResponseEntity<Student> updateStudent(@PathVariable Long id, @RequestBody Student studentDetails) {
        Student updatedStudent = studentService.updateStudent(id, studentDetails);
        return updatedStudent != null ? new ResponseEntity<>(updatedStudent, HttpStatus.OK)
                                      : new ResponseEntity<>(HttpStatus.NOT_FOUND);
    }
}

Explanation

• @PutMapping("/{id}"): Handles HTTP PUT requests to update a student’s details.
• @PathVariable: Binds the method parameter to the value of the path variable.
• @RequestBody: Binds the request body to the method parameter.
• ResponseEntity: Wraps the response and sets the appropriate HTTP status. If the student is updated successfully, it returns 200 OK; if the student is not found, it returns 404 Not Found.

Test Using Postman Client

Step-by-Step Testing

1. Open Postman:

   • Launch the Postman client from your installed applications.

2. Create a New Request:

   • Click on "New" and then select "Request".

3. Set Request Type and URL:

   • Set the request type to PUT.
   • Enter the URL: http://localhost:8080/api/students/{id} (replace {id} with the actual student ID).

4. Set Request Body:

   • Click on the "Body" tab.
   • Select "raw" and "JSON".
   • Enter the following JSON data:

{
    "firstName": "UpdatedFirstName",
    "lastName": "UpdatedLastName",
    "email": "updated.email@example.com"
}

5. Send Request:
   • Click the "Send" button.
   • Verify that the response status is 200 OK if the student is updated or 404 Not Found if the student does not exist.

Explanation

• Request Type: PUT indicates that we are updating data.
• URL: Points to the Update Student REST API endpoint with the student ID as a path variable.
• Request Body: Contains the updated student details in JSON format.
• Response: Verifies that the student’s details are updated or that the appropriate error message is shown.

Conclusion

In this chapter, we built an Update Student REST API for our Student Management System Project with a MySQL database. We updated the service layer, built the Update Student REST API, and tested it using the Postman client. Each step was explained in detail. In the next chapter, we will build a Delete Student REST API.