How WebClient is different from RestTemplate?

Overview

WebClient and RestTemplate are two popular ways to make HTTP requests in a Java application. While WebClient and RestTemplate both allow you to interact with RESTful web services, there are some key differences between the two.

What is WebClient?

WebClient is a newer HTTP client introduced in Spring 5. It’s a non-blocking, reactive HTTP client designed for use with Spring WebFlux. WebClient is built on top of Reactor, a reactive library for building non-blocking applications. This means that WebClient is well-suited for use cases where you need to make a large number of requests in parallel. Also, where you want to handle responses asynchronously.

We can use WebClient by adding a single dependency to our project.

<dependency>

   <groupId>org.springframework.boot</groupId>

   <artifactId>spring-boot-starter-webflux</artifactId>

</dependency>

Code snippet for WebClient

// WebClient example

WebClient webClient = WebClient.create();

Mono<String> response = webClient.get()

    .uri("https://jsonplaceholder.typicode.com/todos/1")

    .retrieve()

    .bodyToMono(String.class);

In the WebClient example, we create a new WebClient instance and use it to make an HTTP GET request to the JSONPlaceholder API. We then retrieve the response body as a Mono<String> object, which is a reactive stream that will emit the response body when it’s available. This allows us to handle the response asynchronously, without blocking the calling thread

What is RestTemplate?

RestTemplate, on the other hand, is a more traditional, blocking HTTP client that has been around since Spring 3. It’s built on top of the Apache HttpClient library and provides a simpler, more synchronous API for making HTTP requests. RestTemplate is still widely used in Spring applications, particularly those that use Spring MVC.

We can use RestTemplate by adding a single dependency to our project.

<dependency>

   <groupId>org.springframework.boot</groupId>

   <artifactId>spring-boot-starter-web</artifactId>

</dependency>

Code Snippet for RestTemplate

// RestTemplate example

RestTemplate restTemplate = new RestTemplate();

String response = restTemplate.getForObject("https://jsonplaceholder.typicode.com/todos/1", String.class);

In the RestTemplate example, we create a new RestTemplate instance and use it to make an HTTP GET request to the same URL. We retrieve the response body as a String using the getForObject method. This is a blocking call, which means that the calling thread will be blocked until the response is received.

WebClient Vs RestTemplate

1. Synchronous vs Asynchronous: RestTemplate is a synchronous client that blocks the calling thread until the response is received. Whereas a web client is an asynchronous client that provides a non-blocking approach to I/O. This means that multiple requests can be made simultaneously without blocking the main thread.
2. Reactive vs Non-Reactive: RestTemplate is a traditional, non-reactive client, whereas web clients support reactive programming, which is a programming paradigm that allows for more efficient handling of large amounts of data.
3. Error Handling: RestTemplate handles errors by throwing exceptions, while a web client uses reactive streams to propagate errors, making it easier to handle errors in a reactive way.
4. Serialization and Deserialization: RestTemplate relies on third-party libraries to serialize and deserialize objects, while web clients use Spring’s built-in serialization and deserialization capabilities.
5. Configuration: RestTemplate is typically configured with a RestTemplateBuilder, while web clients are configured using a WebClient.Builder.

Conclusion

In summary, WebClient and RestTemplate are two different HTTP clients that are designed for different use cases. WebClient is a non-blocking, reactive HTTP client that is well-suited for use in Spring WebFlux applications. RestTemplate is a more traditional, blocking HTTP client that is widely used in Spring MVC applications. Happy learning 🙂

For more, you can refer to the Reactive documentation: https://projectreactor.io/docs/core/release/reference/#intro-reactive

For a more technical blog, you can refer to the Knoldus blog: https://blog.knoldus.com/