Curriculum
Building REST APIs is one of the most important skills for modern Java Backend Engineers because nearly every web application, mobile application, cloud platform, SaaS product, e-commerce system, banking application, healthcare platform, and enterprise software solution relies on APIs for communication. Today, backend developers spend a significant portion of their time designing, developing, testing, and maintaining REST APIs.
REST APIs enable different systems to communicate over the internet using standard HTTP protocols. Whether a mobile application requests user data, an e-commerce website retrieves product information, or a banking app processes transactions, REST APIs act as the communication layer between clients and servers.
Understanding Building REST APIs is essential because Spring Boot provides powerful tools that make API development fast, scalable, and production-ready.
API stands for:
Application Programming InterfaceAn API allows two software systems to communicate with each other.
In simple terms:
API = Communication Bridge Between ApplicationsExamples:
APIs make modern software ecosystems possible.
Consider a food delivery application.
When a customer opens the app:
Request Restaurant ListThe mobile application sends a request to the backend API.
Backend API returns:
[
{
"name":"Restaurant A"
},
{
"name":"Restaurant B"
}
]This communication happens through APIs.
REST stands for:
Representational State TransferREST is an architectural style used for designing web services.
It was introduced by:
Roy Fielding
REST provides guidelines for building scalable web services.
A REST API is an API that follows REST principles.
In simple terms:
REST API = Web Service Following REST RulesREST APIs use:
These APIs are lightweight and easy to use.
REST APIs provide several advantages.
Easy to understand.
Supports large applications.
Works across technologies.
Uses JSON.
Widely adopted.
These benefits make REST APIs the preferred choice.
Basic architecture:
Client
|
HTTP Request
|
REST API
|
Business Logic
|
Database
|
HTTP Response
|
ClientThis architecture powers modern web applications.
Examples:
Client sends requests.
Processes requests and returns responses.
Spring Boot applications typically act as servers.
REST follows several principles.
Each request contains all required information.
Example:
Request 1 Independent
Request 2 IndependentServer does not store client session state.
Client and server remain independent.
Benefits:
Uses standard URLs and HTTP methods.
This improves consistency.
A resource represents data exposed through an API.
Examples:
/students
/products
/orders
/customersEach resource has a unique URL.
An endpoint is a URL used to access resources.
Examples:
/students
/students/101
/products
/ordersEndpoints define API functionality.
JSON stands for:
JavaScript Object NotationIt is the most common format used in REST APIs.
Example:
{
"id":101,
"name":"Rahul",
"course":"Java"
}JSON is:
Spring Boot automatically handles JSON conversion.
REST APIs use HTTP methods to perform operations.
Retrieve data.
Example:
GET /studentsReturns student records.
Create data.
Example:
POST /studentsAdds a new student.
Update data.
Example:
PUT /students/101Updates existing data.
Delete data.
Example:
DELETE /students/101Removes data.
These methods form the basis of RESTful APIs.
Status codes indicate request outcomes.
Request successful.
200 OKResource created successfully.
201 CreatedInvalid request.
400 Bad RequestResource does not exist.
404 Not FoundServer-side issue.
500 Internal Server ErrorStatus codes improve API communication.
First, create a controller.
Example:
@RestController
public class StudentController {
}Spring Boot registers this controller automatically.
Example:
@RestControllerPurpose:
Create REST EndpointReturns JSON responses directly.
Widely used in API development.
Example:
@GetMapping("/students")
public String getStudents() {
return "Student List";
}Access:
GET /studentsResponse:
Student ListThis is a simple REST endpoint.
Example:
@GetMapping("/student")
public Student getStudent() {
return new Student(
101,
"Rahul"
);
}Response:
{
"id":101,
"name":"Rahul"
}Spring automatically converts objects to JSON.
Example:
@PostMapping("/students")
public String addStudent() {
return "Student Added";
}POST creates resources.
Commonly used in forms and APIs.
Example:
@PostMapping("/students")
public Student addStudent(
@RequestBody Student student
) {
return student;
}Purpose:
Convert JSON To Java ObjectThis is frequently used in API development.
Request:
{
"id":101,
"name":"Rahul"
}Spring converts JSON into a Java object automatically.
Example:
@PutMapping("/students/{id}")Purpose:
Update Existing ResourcePUT modifies existing records.
Example:
@DeleteMapping("/students/{id}")Purpose:
Delete ResourceDELETE removes data.
Example:
@GetMapping("/students/{id}")Retrieve:
@PathVariable Long idRequest:
/students/101Value:
101Spring extracts the parameter automatically.
Example:
/students?page=1Used for:
Common in enterprise APIs.
Professional APIs follow:
Controller
|
Service
|
Repository
|
DatabaseThis architecture improves maintainability.
Request:
GET /studentsFlow:
Controller
↓
Service
↓
Repository
↓
DatabaseResponse returns through the same layers.
Popular tools:
API testing platform.
REST client.
Useful for GET requests.
Testing ensures API reliability.
Endpoints:
/accounts
/transactions
/customersREST APIs power online banking systems.
Endpoints:
/products
/orders
/paymentsREST APIs enable customer interactions.
Endpoints:
/patients
/doctors
/appointmentsHealthcare systems use APIs extensively.
Supports large user bases.
Easy to understand.
Supports multiple clients.
Lightweight communication.
Used globally.
These advantages explain widespread usage.
Use services for business logic.
Return meaningful responses.
Use RESTful naming conventions.
Prefer structured JSON responses.
Avoiding these mistakes improves API quality.
These practices improve maintainability.
REST API development is one of the most requested backend skills.
Frequently asked during:
A strong understanding of REST APIs significantly improves employability.
Building REST APIs is a fundamental skill in modern backend development. REST APIs allow applications to communicate efficiently using HTTP, JSON, and standardized endpoints.
Key concepts covered include:
Mastering REST APIs is essential before learning database integration, CRUD operations, validation, exception handling, authentication, microservices, and enterprise backend development.
A REST API is a web service that follows REST architectural principles and uses HTTP for communication.
JSON is a lightweight data format commonly used for API communication.
@RestController creates REST endpoints that return JSON responses.
POST is used to create new resources.
REST APIs enable communication between applications, mobile apps, websites, and backend systems.
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