REST API Explained: A Beginner’s Guide With Examples

Introduction

If you've ever logged into an app, checked the weather, ordered food, made a payment, or loaded posts on a social platform, you've probably used an API.

An API (Application Programming Interface) is a way for one software application to communicate with another. A REST API is one of the most common ways to build these communication channels over HTTP.

For example, when a frontend needs a user's profile, it might send:

GET /api/users/42

The server processes the request and returns data, usually as JSON:

{
  "id": 42,
  "name": "Aarav",
  "email": "aarav@example.com"
}

That's the basic idea behind an API: a client sends a request, a server processes it, and the server sends back a response.

This guide explains APIs from the ground up, then moves into REST APIs, HTTP methods, status codes, JSON, authentication, CRUD operations, practical examples, API testing tools, common mistakes, and how REST APIs fit into real applications.

Quick Answer: What Is an API?

An API is a defined interface that allows two software systems to communicate with each other.

For web applications, APIs commonly use HTTP to exchange requests and responses.

A typical flow looks like this:

Client
  |
  | HTTP Request
  v
API Server
  |
  | Process request
  v
Database
  |
  | Data
  v
API Server
  |
  | HTTP Response
  v
Client

The client could be:

• A web browser

• React application

• Android app

• iOS app

• Another backend service

• A command-line application

• An IoT device

The API acts as the communication boundary between these systems.

What Is an API?

API stands for Application Programming Interface.

Don't let the name make it sound more complicated than it is.

An API is essentially a contract between software components.

The contract defines things such as:

• What requests are allowed

• Where requests should be sent

• What data can be provided

• What response will be returned

• What errors can occur

• What authentication is required

For example, suppose an application exposes:

GET /api/products

The API documentation might say that this endpoint returns a list of products.

A client doesn't need to know how the server retrieves those products.

It only needs to know how to communicate with the API.

That's an important idea.

The client doesn't need to know how the server works internally. It only needs to know how to use the API.

A Simple Real-World API Example

Think about a food delivery application.

The mobile app needs to display nearby restaurants.

The app could request:

GET /api/restaurants?city=pune

The server might:

1. Receive the request.

2. Validate the city.

3. Query the database.

4. Find matching restaurants.

5. Convert the data into JSON.

6. Return an HTTP response.

The application receives something like:

{
  "restaurants": [
    {
      "id": 101,
      "name": "Pizza House",
      "rating": 4.5
    },
    {
      "id": 102,
      "name": "Spice Kitchen",
      "rating": 4.3
    }
  ]
}

The mobile application doesn't care whether the backend uses Java, Node.js, Python, Go, or .NET.

It only cares about the API contract.

How Does an API Work?

A typical web API follows a request-response model.

┌──────────────┐
│    Client    │
│ React / App  │
└──────┬───────┘
       │
       │ HTTP Request
       ▼
┌──────────────┐
│   REST API   │
│   Server     │
└──────┬───────┘
       │
       │ Database Query
       ▼
┌──────────────┐
│   Database   │
└──────┬───────┘
       │
       │ Result
       ▼
┌──────────────┐
│   REST API   │
└──────┬───────┘
       │
       │ JSON Response
       ▼
┌──────────────┐
│    Client    │
└──────────────┘

For example:

GET /api/users/10

The server might return:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 10,
  "name": "Rahul",
  "role": "Developer"
}

The important parts are:

Request → Processing → Response

What Is a REST API?

REST stands for Representational State Transfer.

REST is an architectural style for designing networked applications.

REST APIs commonly use:

• HTTP

• URLs

• HTTP methods

• Status codes

• JSON

• Stateless communication

A REST API exposes resources through URLs.

For example:

/users
/products
/orders
/payments
/articles
/comments

A client then uses HTTP methods to interact with those resources.

For example:

GET /users
POST /users
GET /users/10
PUT /users/10
DELETE /users/10

This is where REST becomes useful.

Instead of creating completely different URLs for every action, you model the application around resources.

REST API Example

Suppose we're building an e-commerce application.

Our resource is:

products

We might design the API like this:

REST API Product Operations

Get all products

GET /api/products

Get one product

GET /api/products/10

Create a product

POST /api/products

Update a product

PUT /api/products/10

Partially update a product

PATCH /api/products/10

Delete a product

DELETE /api/products/10

Notice something interesting.

The URL doesn't change much.

The HTTP method tells the server what operation the client wants to perform.

HTTP Methods Explained

HTTP methods are one of the most important concepts when learning REST APIs.

GET

Used to retrieve data.

GET /api/products

Response:

[
  {
    "id": 1,
    "name": "Laptop"
  },
  {
    "id": 2,
    "name": "Keyboard"
  }
]

A GET request normally shouldn't modify server data.

POST

Used to create a new resource.

POST /api/products

Request body:

{
  "name": "Mechanical Keyboard",
  "price": 4999
}

Possible response:

{
  "id": 25,
  "name": "Mechanical Keyboard",
  "price": 4999
}

PUT

Usually used to replace an existing resource.

PUT /api/products/25

Request:

{
  "name": "Mechanical Keyboard Pro",
  "price": 5999
}

PATCH

Used for a partial update.

For example, if you only want to change the price:

PATCH /api/products/25

{
  "price": 5499
}

DELETE

Used to remove a resource.

DELETE /api/products/25

A successful response might be:

204 No Content

HTTP Status Codes

An API doesn't communicate only through JSON.

It also uses HTTP status codes.

Some of the most important ones are:

200 → Success

201 → Resource Created

204 → Success, No Content

400 → Bad Request

401 → Authentication Required/Invalid

403 → Access Forbidden

404 → Resource Not Found

409 → Conflict

422 → Validation Error

429 → Too Many Requests

500 → Server Error

503 → Service Unavailable

For example:

GET /api/users/999

If user 999 doesn't exist:

HTTP/1.1 404 Not Found

The API might return:

{
  "message": "User not found"
}

This is much better than returning:

200 OK

for every situation.

The status code itself communicates important information to the client.

What Is JSON?

JSON stands for JavaScript Object Notation.

It's one of the most common formats used by REST APIs.

Example:

{
  "id": 101,
  "name": "Aarav",
  "email": "aarav@example.com",
  "active": true
}

JSON supports common data types such as:

• Strings

• Numbers

• Booleans

• Arrays

• Objects

• null

For example:

{
  "name": "Laptop",
  "price": 75000,
  "available": true,
  "tags": ["electronics", "computer"]
}

JSON became extremely popular for APIs because it's relatively compact, human-readable, and supported by practically every modern programming language.

API Endpoints

An endpoint is a specific URL through which an API exposes functionality or a resource.

For example:

GET /api/users

is an endpoint.

Another:

GET /api/users/42

retrieves a specific user.

A practical API might contain:

/api/users
/api/products
/api/orders
/api/payments
/api/auth/login
/api/auth/register

Good endpoint names usually represent resources rather than actions.

Prefer:

GET /api/users/42

over something like:

GET /api/getUserById?id=42

The first design fits the resource-oriented style of REST better.

Path Parameters vs Query Parameters

This is a common source of confusion when you're starting out.

Path Parameter

A path parameter identifies a specific resource.

GET /api/users/42

Here:

42

is the user ID.

Another example:

GET /api/products/100

Query Parameter

Query parameters usually modify or filter a request.

GET /api/products?category=laptops

Multiple parameters:

GET /api/products?category=laptops&page=2&limit=20

Here:

category=laptops
page=2
limit=20

are query parameters.

A simple rule:

Path parameter → Which resource?

Query parameter → How should I filter or modify the result?

HTTP Headers

Headers carry additional information about an HTTP request or response.

For example:

Content-Type: application/json

This tells the server that the request body contains JSON.

Authentication might use:

Authorization: Bearer eyJhbGciOi...

A request can contain several headers:

Content-Type: application/json
Accept: application/json
Authorization: Bearer <token>

Headers are especially important when working with authentication, caching, content negotiation, and security.

Request Body

A request body contains data sent to the server.

For example:

POST /api/users
Content-Type: application/json

{
  "name": "Aarav",
  "email": "aarav@example.com",
  "password": "secret123"
}

The server receives this data, validates it, and performs the requested operation.

You generally see request bodies with methods such as:

• POST

• PUT

• PATCH

REST API Authentication

Many APIs aren't public.

The server needs to know who is making a request.

Common authentication approaches include:

• API keys

• Session cookies

• OAuth 2.0

• JWT

• Basic authentication

• Mutual TLS in some specialized systems

A common modern pattern is a bearer token.

GET /api/profile
Authorization: Bearer <access-token>

The server validates the token before returning protected information.

For example:

Client
  │
  │ Login credentials
  ▼
Auth API
  │
  │ Access Token
  ▼
Client
  │
  │ Authorization: Bearer token
  ▼
Protected API
  │
  │ Validate token
  ▼
Response

Authentication and authorization aren't the same thing.

Authentication asks:

Who are you?

Authorization asks:

What are you allowed to do?

That's an important distinction when you start building production APIs.

Building a REST API With Spring Boot

If you're learning Java backend development, Spring Boot is one of the most useful frameworks to practice REST APIs with.

Suppose we want an endpoint that returns users.

A simple controller could look like this:

@RestController
@RequestMapping("/api/users")
public class UserController {

    @GetMapping
    public List<User> getUsers() {
        return List.of(
            new User(1L, "Aarav"),
            new User(2L, "Priya")
        );
    }
}

A request to:

GET /api/users

could return:

[
  {
    "id": 1,
    "name": "Aarav"
  },
  {
    "id": 2,
    "name": "Priya"
  }
]

The important annotations are:

@RestController

This tells Spring that the class handles HTTP requests and that returned objects should generally be written to the response body.

@RequestMapping("/api/users")

Defines the base URL.

@GetMapping

Maps GET requests to the method.

If you're following TheTechLane's Java series, this is where the earlier Java fundamentals start becoming practical. Understanding how Java programs are compiled and executed also makes the backend stack much easier to reason about.

You can continue with:

• Java Compilation Process

• Bytecode Explained

• Install Java JDK

The connection is straightforward:

Java
  ↓
Spring Boot
  ↓
REST Controller
  ↓
Business Logic
  ↓
Database
  ↓
JSON Response

REST API CRUD Example

CRUD stands for:

• Create

• Read

• Update

• Delete

These four operations appear everywhere in backend development.

Suppose we have:

/api/articles

Our API could look like this:

POST   /api/articles
GET    /api/articles
GET    /api/articles/10
PUT    /api/articles/10
PATCH  /api/articles/10
DELETE /api/articles/10

The application might follow this architecture:

                 ┌───────────────┐
                 │ React / Mobile│
                 │    Client     │
                 └───────┬───────┘
                         │
                    HTTP / JSON
                         │
                         ▼
                 ┌───────────────┐
                 │ REST Controller│
                 └───────┬───────┘
                         │
                         ▼
                 ┌───────────────┐
                 │    Service    │
                 │    Layer      │
                 └───────┬───────┘
                         │
                         ▼
                 ┌───────────────┐
                 │  Repository   │
                 └───────┬───────┘
                         │
                         ▼
                 ┌───────────────┐
                 │   PostgreSQL  │
                 └───────────────┘

This separation is useful because the controller shouldn't contain every piece of business logic.

A typical Spring Boot project might look like:

src/main/java
└── com.example.app
    ├── controller
    │   └── UserController.java
    ├── service
    │   └── UserService.java
    ├── repository
    │   └── UserRepository.java
    ├── entity
    │   └── User.java
    └── dto
        └── UserResponse.java

This is much easier to maintain as the application grows.

How to Test a REST API

You don't need a frontend to test an API.

That's one of the nice things about backend development.

You can test an API directly.

For example:

curl https://api.example.com/users

Or:

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"Aarav","email":"aarav@example.com"}'

But manually writing curl commands isn't always convenient.

That's where API testing tools become useful.

Useful API Tools Developers Actually Use

1. Postman

Postman is one of the most popular API development and testing tools.

You can:

• Send GET requests

• Send POST/PUT/PATCH requests

• Add headers

• Add authentication

• Send JSON request bodies

• Save collections

• Write API tests

• Manage environments

• Inspect responses

For example:

Method: POST

URL:
http://localhost:8080/api/users

Body:
{
  "name": "Aarav",
  "email": "aarav@example.com"
}

If you're learning Spring Boot, I'd strongly recommend using Postman while building your first REST API.

You can immediately see what your backend actually returns instead of guessing from the frontend.

2. Insomnia

Insomnia is another API client.

It's particularly useful if you prefer a simpler interface for working with HTTP APIs.

You can use it for:

• REST APIs

• GraphQL

• Authentication

• Environment variables

• API requests

• Debugging

Postman and Insomnia solve many of the same problems.

You don't need both when you're starting.

Pick one and become comfortable with it.

3. Swagger / OpenAPI

OpenAPI Initiative provides the OpenAPI specification for describing HTTP APIs.

Swagger tooling is commonly used to document and interact with APIs.

A documented API might show:

GET /api/users

200 OK
Returns a list of users

and:

POST /api/users

Request Body:
{
  "name": "string",
  "email": "string"
}

This is especially useful when multiple developers work on the same backend.

Instead of asking:

What endpoint should I call?

you can look at the API documentation.

For Spring Boot projects, Springdoc OpenAPI is a popular option for generating OpenAPI documentation.

4. curl

curl documentation is a command-line tool for transferring data over network protocols, including HTTP.

It's available on most developer machines and is extremely useful for quick API testing.

Example:

curl -X GET http://localhost:8080/api/users

POST:

curl -X POST http://localhost:8080/api/users \
  -H "Content-Type: application/json" \
  -d '{"name":"Aarav"}'

You don't need a graphical application for every API request.

Sometimes a single curl command is faster.

5. Browser DevTools

Your browser is already an excellent API debugging tool.

Open:

Chrome → Developer Tools → Network

Then reload a webpage.

You'll see requests such as:

GET /api/articles
GET /api/user/profile
POST /api/login

Click one and inspect:

• Request URL

• Method

• Status code

• Request headers

• Response headers

• Request payload

• Response body

• Timing

This is one of the first debugging techniques I'd recommend learning.

When a frontend isn't displaying data, don't immediately assume the React code is broken.

Open the Network tab.

The API might be returning:

401 Unauthorized

or:

500 Internal Server Error

That changes the debugging direction completely.

API Documentation You Should Bookmark

When learning APIs, don't rely only on tutorials.

Official documentation is where you should eventually go for exact behavior.

Useful references include:

• MDN HTTP documentation — excellent for understanding HTTP requests, responses, headers, methods, and status codes.

• HTTP Semantics — RFC 9110 — the formal HTTP specification.

• OpenAPI Specification — useful for describing and documenting APIs.

• Spring REST documentation — useful when building REST APIs with Spring.

• Postman Learning Center — practical API testing and development guidance.

• curl documentation — command-line HTTP tooling and reference.

A good learning pattern is:

Tutorial
   ↓
Build something
   ↓
Break something
   ↓
Read official documentation
   ↓
Fix it
   ↓
Build again

That's much more useful than memorizing definitions.

REST API vs SOAP

REST and SOAP are both used for communication between systems, but they're different approaches.

REST

Type → Architectural style
Common format → JSON
Transport → Commonly HTTP
Complexity → Generally simpler
Browser/mobile APIs → Very common
Contract → Often OpenAPI
Typical use → Modern web and mobile APIs

SOAP

Type → Protocol
Common format → XML
Transport → HTTP and other protocols
Complexity → More formal
Browser/mobile APIs → Less common
Contract → WSDL
Typical use → Enterprise and legacy systems

REST is often the first approach developers learn for modern web APIs.

That doesn't mean SOAP is useless.

You'll still encounter SOAP in some enterprise systems, banking integrations, government systems, and older applications.

What Makes a REST API "RESTful"?

REST isn't simply:

"An API that returns JSON."

That's an oversimplification.

REST is an architectural style with several constraints.

Some important ideas include:

Client-Server

The client and server have separate responsibilities.

Client → UI and user interaction

Server → Data and business logic

Statelessness

Each request should contain the information necessary for the server to process it.

The server shouldn't depend on hidden client session state between requests in the REST model.

Cacheability

Responses can indicate whether they may be cached.

Uniform Interface

Resources should be exposed through consistent interfaces.

For example:

GET    /users
POST   /users
GET    /users/10
PUT    /users/10
DELETE /users/10

These constraints are part of what makes REST different from simply creating HTTP endpoints.

API Versioning

APIs change.

Suppose you initially have:

/api/users

Later, you make a breaking change.

One approach is:

/api/v2/users

For example:

GET /api/v1/products

and:

GET /api/v2/products

Versioning helps clients migrate without immediately breaking existing integrations.

But don't add versions automatically just because you can.

A good API design considers backward compatibility before introducing a new version.

Pagination

Imagine your database contains 10 million users.

You probably don't want this:

GET /api/users

to return all 10 million records.

Instead, use pagination.

GET /api/users?page=1&limit=20

Response:

{
  "data": [
    {
      "id": 1,
      "name": "Aarav"
    }
  ],
  "page": 1,
  "limit": 20,
  "total": 5000
}

Pagination reduces the amount of data transferred and makes APIs easier for clients to consume.

For large datasets, cursor-based pagination can be more appropriate than traditional page-number pagination.

API Error Handling

A good API doesn't just say:

{
  "error": "Something went wrong"
}

A consistent error format is much easier for frontend developers and other API consumers.

For example:

{
  "timestamp": "2026-08-10T10:30:00Z",
  "status": 400,
  "error": "Bad Request",
  "message": "Email address is invalid",
  "path": "/api/users"
}

The exact structure is a design decision, but consistency matters.

If every endpoint returns errors differently, clients become unnecessarily complicated.

REST API Security Best Practices

Never treat API security as an afterthought.

Some important practices include:

Use HTTPS

Don't send sensitive information over plain HTTP.

Use:

https://api.example.com

instead of:

http://api.example.com

for production traffic.

Validate Input

Never trust data coming from the client.

For example:

{
  "age": -500
}

Your backend should validate it.

Authenticate Protected Endpoints

Sensitive endpoints should require appropriate authentication.

Authorize Actions

A logged-in user shouldn't automatically have permission to perform every operation.

Don't Expose Secrets

Never put things such as:

DATABASE_PASSWORD
JWT_SECRET
API_SECRET

inside frontend code or public repositories.

Rate Limit Sensitive Endpoints

Login, password reset, OTP, and other sensitive endpoints may need rate limiting to reduce abuse.

REST API Best Practices

Here are practices worth following when designing APIs.

1. Use nouns for resources

Prefer:

/api/users

instead of:

/api/getUsers

2. Use HTTP methods correctly

GET    → Read
POST   → Create
PUT    → Replace
PATCH  → Partial update
DELETE → Delete

3. Return meaningful status codes

Don't return 200 OK for every situation.

4. Keep response formats consistent

If one endpoint returns:

{
  "data": []
}

and another returns:

{
  "results": []
}

without a good reason, the API becomes harder to consume.

5. Validate input

Never assume the client sends valid data.

6. Document the API

Use OpenAPI/Swagger or another clear documentation system.

7. Version carefully

Breaking changes need a migration strategy.

8. Don't expose internal implementation details

The API should expose a stable contract rather than your database structure.

Common REST API Mistakes

One mistake I see often is treating the API as nothing more than a collection of URLs.

It's more than that.

The API is a contract.

Here are some common problems.

Mistake 1: Using GET to modify data

Bad:

GET /api/deleteUser?id=10

Better:

DELETE /api/users/10

Mistake 2: Returning 200 for errors

Bad:

HTTP/1.1 200 OK

{
  "error": "User not found"
}

Better:

HTTP/1.1 404 Not Found

Mistake 3: Returning huge datasets

Use pagination, filtering, and limits.

Mistake 4: Ignoring authentication

Never assume that hiding an endpoint URL makes it secure.

Mistake 5: Putting business logic in controllers

A controller should generally coordinate HTTP concerns rather than contain the entire application.

A cleaner architecture is:

Controller
    ↓
Service
    ↓
Repository
    ↓
Database

Mistake 6: Not testing APIs independently

Test your backend before debugging the frontend.

Postman, curl, Swagger UI, and browser DevTools make this much easier.

REST API in a Real Application

Let's put everything together.

Imagine an online learning platform.

The frontend might call:

POST /api/auth/login

Then:

GET /api/courses

Then:

GET /api/courses/42

Then:

POST /api/courses/42/enroll

The architecture could look like:

                    ┌───────────────┐
                    │ Web / Mobile  │
                    │    Client     │
                    └───────┬───────┘
                            │
                       HTTPS / JSON
                            │
                            ▼
                 ┌────────────────────┐
                 │     API Gateway    │
                 └─────────┬──────────┘
                           │
              ┌────────────┼────────────┐
              ▼            ▼            ▼
        ┌──────────┐ ┌──────────┐ ┌──────────┐
        │  Auth    │ │ Courses  │ │ Payments │
        │ Service  │ │ Service  │ │ Service  │
        └────┬─────┘ └────┬─────┘ └────┬─────┘
             │             │            │
             ▼             ▼            ▼
        ┌─────────┐   ┌─────────┐  ┌─────────┐
        │  DB     │   │  DB     │  │  DB     │
        └─────────┘   └─────────┘  └─────────┘

This is where REST APIs become especially important in backend development.

The frontend doesn't need to know how the database works.

The payment service doesn't need to know how the frontend is rendered.

Each component communicates through defined interfaces.

REST API vs GraphQL

You may also encounter GraphQL when working with APIs.

1. Rest API

REST

↓

Multiple Endpoints

↓

Server Defines Response

↓

Usually Simpler

↓

Great for Resource-Oriented APIs

2. GraphQL

GraphQL

↓

Often One Endpoint

↓

Client Defines Required Fields

↓

More Flexible Queries

↓

Great for Complex Data Requirements

Neither is universally better.

The right choice depends on the application.

For learning backend development, REST is a very good place to start because it teaches the fundamentals of HTTP, resources, requests, responses, status codes, authentication, and API design.

A Practical API Learning Stack

If you're learning APIs today, you don't need dozens of tools.

A simple stack is enough:

Useful API Development Tools

Browser DevTools

→ Inspect real API requests and responses directly from the browser.

Postman

→ Build, send, test, and organize API requests.

curl

→ Test APIs quickly from the terminal.

Swagger / OpenAPI

→ Document APIs and provide an interactive way to explore endpoints.

Spring Boot

→ Build Java-based REST APIs and backend applications.

PostgreSQL

→ Store and manage application data used by your APIs.

Git

→ Track changes and collaborate on API and backend code.

For a Java backend learner, a very practical progression is:

Java
 ↓
HTTP Fundamentals
 ↓
REST API
 ↓
Spring Boot
 ↓
Spring Data JPA
 ↓
PostgreSQL
 ↓
Spring Security
 ↓
JWT / OAuth
 ↓
Docker
 ↓
Microservices

Once these pieces start connecting, backend development becomes much easier to understand.

Try It Yourself

Here's a small exercise.

Build a simple Book API.

Create these endpoints:

GET    /api/books
GET    /api/books/{id}
POST   /api/books
PUT    /api/books/{id}
DELETE /api/books/{id}

A book could look like:

{
  "title": "Clean Code",
  "author": "Robert C. Martin",
  "price": 799
}

Then test every endpoint using Postman.

Your goal isn't to build a huge application.

Your goal is to understand the complete cycle:

HTTP Request
     ↓
Controller
     ↓
Service
     ↓
Repository
     ↓
Database
     ↓
JSON Response

Once you understand that cycle, you have the foundation for much larger backend applications.

API Interview Questions

If you're preparing for backend or software engineering interviews, know these questions.

1. What is an API?

An API is an interface that allows software components to communicate using defined rules and contracts.

2. What is REST?

REST is an architectural style for designing distributed systems, commonly used with HTTP APIs.

3. What is a REST API?

A REST API is an HTTP-based API designed around resources and REST principles.

4. What is the difference between PUT and PATCH?

PUT generally replaces a resource, while PATCH applies a partial modification.

5. What is the difference between 401 and 403?

401 Unauthorized generally means authentication is required or invalid.

403 Forbidden means the request is understood but the authenticated client isn't permitted to perform the operation.

6. What is idempotency?

An operation is idempotent when repeating it has the same intended effect as performing it once.

For example, replacing a resource with the same PUT request should result in the same resource state.

7. What is an API endpoint?

An endpoint is a specific network location and HTTP operation through which a client interacts with an API.

8. What is JSON?

JSON is a lightweight text format commonly used for exchanging structured data.

9. What is statelessness in REST?

Each request should contain the information required to process it without relying on hidden server-side client state from previous requests.

10. How do you test an API?

You can use tools such as Postman, curl, Swagger UI, automated test frameworks, and browser DevTools.

Frequently Asked Questions

Is an API the same as a REST API?

No.

API is the broader concept. REST is one architectural approach for building APIs.

Other approaches include GraphQL, SOAP, gRPC, and WebSockets.

Is REST API always JSON?

No.

REST APIs can technically exchange different representations.

JSON is simply extremely common for modern web APIs.

Is HTTP required for REST?

REST itself isn't synonymous with HTTP, but HTTP is by far the most common protocol used to implement RESTful web APIs.

Is Postman an API?

No.

Postman is a tool used to develop, test, document, and work with APIs.

Can a frontend call an API directly?

Yes.

A React application, mobile application, or browser can make HTTP requests to an API, assuming the API permits the request and the necessary security policies are satisfied.

Can one API call another API?

Yes.

This is common in backend systems.

For example:

Frontend
   ↓
Order API
   ↓
Payment API
   ↓
Payment Provider

What language is used to create REST APIs?

Almost any modern backend language can create REST APIs.

Examples include:

• Java

• JavaScript/Node.js

• Python

• Go

• C#

• PHP

• Ruby

• Kotlin

• Rust

The API consumer doesn't normally need to know which language powers the server.

What should I learn before REST APIs?

You should understand basic programming and have a basic idea of HTTP.

For Java developers, learning Java first and then moving into Spring Boot is a practical path.

Is REST API difficult to learn?

The basic concepts aren't difficult.

The challenging part comes later: authentication, authorization, validation, database design, caching, rate limiting, observability, versioning, distributed systems, and API security.

Start with CRUD and HTTP first.

Is REST still used in 2026?

Yes. REST remains a major approach for web APIs and backend integrations.

Modern systems may also use GraphQL, gRPC, event-driven messaging, WebSockets and other communication patterns alongside REST.

Key Takeaways

An API is a communication interface between software systems.

REST is an architectural style commonly used to build web APIs.

The fundamentals you should remember are:

API
 ↓
HTTP
 ↓
Endpoint
 ↓
Request
 ↓
Server Processing
 ↓
Response

The most important HTTP methods are:

GET     → Read
POST    → Create
PUT     → Replace
PATCH   → Partial Update
DELETE  → Delete

And common status codes include:

200 → Success
201 → Created
204 → No Content
400 → Bad Request
401 → Unauthorized
403 → Forbidden
404 → Not Found
500 → Server Error

If you're learning backend development, don't stop at memorizing these definitions.

Build an API.

Send requests.

Break it.

Read the response.

Open DevTools.

Test it with Postman.

Then read the official documentation to understand why it behaves that way.

That's when REST APIs actually start making sense.

Previous Lesson

If you're following TheTechLane's Java learning path, this topic fits naturally after understanding how Java applications are built and executed.

You can revisit:

Java Compilation Process

and:

Bytecode Explained

You can also start from the environment setup:

Install Java JDK

These topics aren't directly required to understand REST, but they build the Java foundation you'll need when you start creating REST APIs with Spring Boot.

What's Next?

Once you understand REST APIs, the next logical step is to build one.

A good progression is:

REST API Fundamentals
        ↓
Spring Boot REST API
        ↓
Controller + Service + Repository
        ↓
Spring Data JPA
        ↓
PostgreSQL
        ↓
Validation + Exception Handling
        ↓
Spring Security
        ↓
JWT Authentication
        ↓
Docker
        ↓
Microservices

That's where the theory turns into actual backend engineering.

Continue Learning

For API development, keep these tools close:

• Postman for testing requests

• Swagger/OpenAPI for API documentation

• curl for command-line testing

• Browser DevTools for debugging frontend-to-backend communication

• Spring Boot for building Java REST APIs

• PostgreSQL for persistent data

And don't underestimate the official documentation. Tutorials teach you the path; documentation tells you exactly how the technology behaves.

Have a Question?

If you run into any issues while writing or running your first Java program, leave a comment below.

We'll help you troubleshoot the problem with clear explanations and practical solutions so you can continue your Java learning journey with confidence.

Happy Coding! ☕

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