Build Get Single Student REST API

Introduction

In this chapter, we will build a Get Single Student REST API for our Student Management System Project with a MySQL database. We will update the service layer, build the Get Single 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 Get All Students REST API.

What We Will Cover in This Chapter

• Update a Service Layer (interface and implementation class)
• Build Get Single 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.Optional;

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

Explanation

• Service Interface: Defines the contract for the service layer. It now includes the getStudentById method to retrieve a student by ID.

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.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);
    }
}

Explanation

• getStudentById Method: Implements the getStudentById method defined in the StudentService interface to retrieve a student by ID using the repository.

Build Get Single 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.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));
    }
}

Explanation

• @GetMapping("/{id}"): Handles HTTP GET requests to retrieve a student by ID.
• @PathVariable: Binds the method parameter to the value of the path variable.
• ResponseEntity: Wraps the response and sets the appropriate HTTP status. If the student is found, it returns 200 OK; if not, 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 GET.
   • Enter the URL: http://localhost:8080/api/students/{id} (replace {id} with the actual student ID).

4. Send Request:

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

Explanation

• Request Type: GET indicates that we are retrieving data.
• URL: Points to the Get Single Student REST API endpoint with the student ID as a path variable.
• Response: Verifies that the correct student data is returned or that the appropriate error message is shown.

Conclusion

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