Web services are used for communication between applications over a network. In Java backend development, REST and SOAP are two popular approaches for building APIs.

Many companies ask REST vs SOAP interview questions to test understanding of API architecture and web service communication.

In this article, we will understand the complete difference between REST API and SOAP Web Services with examples, advantages, disadvantages, and real-world use cases.

What is REST API?

REST stands for:

$REST = Representational\ State\ Transfer$ REST=Representational State Transfer

REST is an architectural style used to build lightweight and scalable web services.

REST APIs use HTTP methods for communication.

Common HTTP Methods

Method	Purpose
GET	Fetch Data
POST	Create Data
PUT	Update Data
DELETE	Remove Data

Example of REST API

GET /users/101

Response:

{
  "id": 101,
  "name": "John"
}

REST mostly uses:

JSON
XML (optional)

But JSON is more popular because it is lightweight.

What is SOAP Web Service?

SOAP stands for:

$SOAP = Simple\ Object\ Access\ Protocol$ SOAP=Simple Object Access Protocol

SOAP is a protocol used for exchanging structured information between systems.

SOAP strictly uses XML format.

Example of SOAP Request

<soap:Envelope>
   <soap:Body>
      <getUser>
         <id>101</id>
      </getUser>
   </soap:Body>
</soap:Envelope>

SOAP requests are more structured and secure.

REST vs SOAP – Complete Difference

Feature	REST API	SOAP Web Service
Type	Architectural Style	Protocol
Data Format	JSON, XML	Only XML
Speed	Faster	Slower
Performance	Lightweight	Heavy
Security	Basic Security	High Security
Flexibility	More Flexible	Strict Rules
Protocol Support	HTTP	HTTP, SMTP, TCP
Learning Curve	Easy	Complex
Scalability	High	Moderate
Best For	Web & Mobile Apps	Enterprise Applications

Why REST APIs Are More Popular

REST APIs are widely used because:

Faster communication
Lightweight payload
Better scalability
Easy integration
Mobile-friendly
Frontend-friendly

Real-Time Example of REST API

E-Commerce Application

Applications like:

Product Service
Order Service
Payment Service

communicate using REST APIs.

Example:

GET /products/10

Returns product details instantly.

Real-Time Example of SOAP

SOAP is commonly used in:

Banking Systems
Insurance Applications
Payment Gateways
Government Applications

Because these systems require:

High security
Transaction reliability
Strict contracts

What is WSDL in SOAP?

WSDL stands for:

$WSDL = Web\ Services\ Description\ Language$ WSDL=Web Services Description Language

It defines:

Service methods
Request format
Response format
Endpoint details

SOAP clients use WSDL to understand service structure.

What is Statelessness in REST?

REST APIs are stateless.

Meaning:

Each request contains complete information.

Server does not store client session.

Benefit

Better scalability
Easier load balancing
Improved performance

Advantages of REST API

1. Lightweight

Uses JSON which is smaller than XML.

2. Faster Performance

Consumes less bandwidth.

3. Easy to Develop

Simple HTTP methods.

4. Highly Scalable

Suitable for microservices architecture.

5. Better for Mobile Apps

Smaller responses improve mobile performance.

Advantages of SOAP

1. High Security

Supports:

WS-Security
Encryption
Digital signatures

2. Reliable Transactions

Suitable for financial applications.

3. Strict Contract

WSDL ensures proper communication structure.

Disadvantages of REST

Less secure compared to SOAP
No strict contract
Different response structures possible

Disadvantages of SOAP

Complex implementation
Heavy XML payload
Slower performance
Difficult to maintain

REST API in Spring Boot

Spring Boot makes REST API development easy.

Example

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

    @GetMapping("/{id}")
    public String getUser(@PathVariable int id) {
        return "User Id: " + id;
    }
}

Output:

User Id: 101

SOAP Web Service in Spring Boot

SOAP services usually use:

Spring Web Services
JAXB
XML schemas

SOAP configuration is more complex than REST.

REST API Interview Questions

Q1. Why REST APIs are stateless?

Because server does not store client session data.

Q2. Which format is mostly used in REST?

JSON format.

Q3. Which is faster REST or SOAP?

REST is faster because it uses lightweight JSON.

Q4. Which is more secure?

SOAP is generally more secure because of WS-Security support.

Q5. Which architecture is preferred in Microservices?

REST APIs are commonly used in Microservices architecture.

When to Use REST API

Use REST when:

Building web applications
Building mobile apps
Creating microservices
Performance is important
Lightweight communication needed

When to Use SOAP

Use SOAP when:

High security required
Enterprise systems involved
Transaction reliability important
Strict contracts needed

Conclusion

Both REST and SOAP are important technologies in Java backend development.

REST APIs are more popular in modern applications because they are:

Lightweight
Fast
Scalable
Easy to maintain

SOAP is still used in enterprise systems requiring:

Strong security
Reliable messaging
Strict communication contracts

Understanding REST vs SOAP is very important for Java, Spring Boot, and Microservices interviews.

Difference Between REST API and SOAP Web Services in Java