WebClient vs RestTemplate: A Detailed Guide

Introduction

In the landscape of Spring applications, RestTemplate was once the standard for handling HTTP requests. However, with the advent of Spring 5, WebClient emerged as a modern, more capable alternative. This article provides a comprehensive comparison between WebClient and RestTemplate, detailing their advantages, disadvantages, usage examples, and unit tests to guide developers on when to use each.

RestTemplate

RestTemplate is a synchronous HTTP client historically favored by Spring developers for consuming RESTful web services.

Pros:

• Simplicity: RestTemplate offers a straightforward API for making synchronous HTTP requests.
• Familiarity: Many Spring developers are already comfortable using RestTemplate.
• Integration with Other Spring Features: RestTemplate works seamlessly with other Spring features like dependency injection.

Cons:

• Synchronous and Blocking: Each RestTemplate request blocks a thread until the response is received, which can limit scalability.
• Lack of Reactive Support: RestTemplate does not support reactive programming paradigms.
• Deprecated in Newer Versions: As of Spring 5, RestTemplate is deprecated in favor of the newer WebClient.

Example Usage:

RestTemplate restTemplate = new RestTemplate();
String result = restTemplate.getForObject("https://jsonplaceholder.typicode.com/posts/1", String.class);

RestTemplate Unit Test:

import org.junit.jupiter.api.Test;
import org.springframework.web.client.RestTemplate;
import static org.junit.jupiter.api.Assertions.*;

class RestTemplateTest {
    
    @Test
    void getRequest_ReturnsContent() {
        RestTemplate restTemplate = new RestTemplate();
        
        String result = restTemplate.getForObject("https://jsonplaceholder.typicode.com/posts/1", String.class);
        
        assertTrue(response.getBody().contains("title"));
        assertTrue(response.getStatusCode().is2xxSuccessful());
    }
}

WebClient

Introduced in Spring 5, WebClient is a modern, reactive HTTP client that supports both synchronous and asynchronous requests.

Pros:

• Reactive: WebClient is built on Project Reactor, enabling reactive, non-blocking requests.
• Flexible: Supports both synchronous and asynchronous programming models.
• Fluent API: Provides a fluent, readable API for building requests.
• Superior Performance: The non-blocking model allows better resource utilization and concurrency.

Cons:

• Steep Learning Curve: Reactive programming can be challenging for developers new to the paradigm.
• Compatibility: Some 3rd-party libraries may not yet have full support for reactive types.

Example Usage:

WebClient webClient = WebClient.create("https://jsonplaceholder.typicode.com/posts/1");

Mono<String> result = webClient.get()
        .retrieve()
        .bodyToMono(String.class);

WebClient Unit Test:

import org.junit.jupiter.api.Test;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;
import reactor.test.StepVerifier;

class WebClientTest {
    
    @Test
    void getRequest_ReturnsContent() {
        WebClient webClient = WebClient.create("https://jsonplaceholder.typicode.com/posts/1");
        
        Mono<String> result = webClient.get()
                .retrieve()
                .bodyToMono(String.class);
                
        StepVerifier.create(result)
            .expectNextMatches(content -> content.contains("title"))
            .verifyComplete();
    }
}

When to Use Each

• Use RestTemplate if:
  • You are working on an existing Spring application built with RestTemplate.
  • You need simple synchronous requests and do not require the benefits of reactive programming.
  • You do not anticipate high concurrent load.
• Use WebClient if:
  • You are building a new Spring application or microservice.
  • You anticipate high traffic and need a scalable solution.
  • You want to leverage the power of reactive programming for better performance and resource utilization.
  • You require a mix of synchronous and asynchronous requests.

Comparison

References

• Spring WebClient vs RestTemplate
• Exploring the Spring 5 WebClient