RestTemplate vs WebClient

Introduction

In this guide, we will explore two popular ways to make HTTP requests in Spring Boot: RestTemplate and WebClient. Both are used to interact with RESTful web services, but they have different features and use cases. We will compare them in simple terms, making it easy for beginners to understand when to use each one.

What is RestTemplate?

RestTemplate is a synchronous client that is used to make HTTP requests in a Spring Boot application. It was introduced in Spring 3 and has been a popular choice for many years. However, it is being deprecated in favor of WebClient for newer applications.

Key Features of RestTemplate

1. Synchronous: RestTemplate is a blocking client, which means it waits for the server to respond before proceeding. This can lead to slower performance when dealing with multiple requests.

2. Easy to Use: It provides simple methods to perform common HTTP operations like GET, POST, PUT, DELETE, etc.

3. Configuration: It allows you to configure timeouts, headers, and other request parameters.

Example of RestTemplate

Here's a simple example of how to use RestTemplate to make a GET request:

import org.springframework.web.client.RestTemplate;

public class RestTemplateExample {

    public static void main(String[] args) {
        RestTemplate restTemplate = new RestTemplate();
        String url = "https://jsonplaceholder.typicode.com/posts/1";
        
        String response = restTemplate.getForObject(url, String.class);
        System.out.println("Response: " + response);
    }
}

Explanation:

• getForObject: This method makes a GET request to the specified URL and returns the response as a string.

What is WebClient?

WebClient is a non-blocking, reactive client introduced in Spring 5 as part of the WebFlux framework. It is designed to be used in reactive applications and offers better performance compared to RestTemplate.

Key Features of WebClient

1. Asynchronous: WebClient is non-blocking, meaning it can handle many requests simultaneously without waiting for each one to finish.

2. Reactive: It is built on top of Project Reactor, making it suitable for reactive programming.

3. Modern: It is the recommended way to make HTTP requests in Spring applications, especially for new projects.

4. Flexible: It supports both synchronous and asynchronous communication, as well as streaming data.

Example of WebClient

Here's a simple example of how to use WebClient to make a GET request:

import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

public class WebClientExample {

    public static void main(String[] args) {
        WebClient webClient = WebClient.create("https://jsonplaceholder.typicode.com");
        
        Mono<String> responseMono = webClient.get()
                                             .uri("/posts/1")
                                             .retrieve()
                                             .bodyToMono(String.class);

        responseMono.subscribe(response -> System.out.println("Response: " + response));
    }
}

Explanation:

• create: Creates a new WebClient instance with the specified base URL.
• get: Initiates a GET request.
• uri: Specifies the endpoint to be called.
• retrieve: Executes the request and retrieves the response.
• bodyToMono: Converts the response body to a Mono<String>.
• subscribe: Subscribes to the Mono to consume the response asynchronously.

RestTemplate vs. WebClient: Key Differences

Feature	RestTemplate	WebClient
Programming	Synchronous	Asynchronous and Reactive
Use Cases	Simple, blocking applications	Modern, reactive applications
Performance	Blocking, can be slower	Non-blocking, better performance
Concurrency	Limited to one request at a time	Can handle multiple requests simultaneously
Streaming	Not supported	Supports streaming of data
Flexibility	Basic HTTP operations	Flexible with advanced options
Spring Version	Introduced in Spring 3, deprecated	Introduced in Spring 5

When to Use RestTemplate vs. WebClient

• RestTemplate:

  • Use in legacy applications where blocking operations are sufficient.
  • Simple use cases with straightforward HTTP operations.

• WebClient:

  • Use in new applications that require non-blocking and reactive operations.
  • Applications that need to handle many concurrent requests efficiently.
  • Projects that require streaming data or advanced HTTP interactions.

Conclusion

In this chapter, we explored RestTemplate and WebClient, two ways to make HTTP requests in Spring Boot applications. While RestTemplate is easy to use and suitable for simple use cases, WebClient offers a modern, non-blocking approach that is better suited for reactive applications. Understanding the differences between these two clients will help you choose the right one for your project. In the next chapter, we will delve deeper into using WebClient in Spring Boot applications.