RestTemplate Deprecated and Its Alternatives

Introduction

In this guide, we will discuss the deprecation of RestTemplate in Spring and explore its alternatives for making HTTP requests. RestTemplate has been a popular choice for many years, but with the advent of reactive programming and new technologies, Spring has introduced more modern solutions. We will look into these alternatives and see how they can be used effectively in Spring Boot applications.

RestTemplate: An Overview

RestTemplate is a synchronous client used for making HTTP requests in Spring applications. It provides a simple interface to perform various HTTP operations such as GET, POST, PUT, DELETE, etc. However, RestTemplate is a blocking client, which means it waits for each request to complete before moving on to the next task. This can lead to performance bottlenecks in applications that require handling multiple concurrent requests.

Why is RestTemplate Deprecated?

• Blocking Nature: RestTemplate is synchronous and blocking, making it less suitable for modern applications that require non-blocking, asynchronous operations.

• Reactive Programming: With the rise of reactive programming, Spring introduced the WebClient in Spring 5 as part of the WebFlux framework. WebClient is a non-blocking, reactive alternative to RestTemplate.

• Future Proofing: The shift towards reactive programming encourages developers to adopt new patterns and technologies that are more aligned with the needs of modern applications.

Alternatives to RestTemplate

1. WebClient

WebClient is a non-blocking, reactive HTTP client introduced in Spring 5. It is designed to work with the reactive programming model and is part of the Spring WebFlux module.

Key Features of WebClient

• Non-blocking: WebClient is asynchronous and can handle multiple requests simultaneously without waiting for each to finish.

• Reactive: Built on top of Project Reactor, making it suitable for reactive programming.

• Modern: It is the recommended way to make HTTP requests in new Spring applications.

Example: Using WebClient

Here's how you can use WebClient to make a simple 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.

2. Feign Client

Feign is a declarative HTTP client developed by Netflix and integrated with Spring Cloud. It simplifies HTTP request processing by using interfaces and annotations.

Key Features of Feign Client

• Declarative: Allows you to define HTTP clients using interfaces and annotations, making the code cleaner and more readable.

• Load Balancing: Integrates seamlessly with Netflix Ribbon for client-side load balancing.

• Integration: Works well with other Spring Cloud components, making it ideal for microservices.

Example: Using Feign Client

Here's how you can use Feign Client to make a simple GET request:

Step 1: Add Dependencies

Add the following dependencies to your pom.xml or build.gradle file:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

Step 2: Enable Feign Client

Enable Feign Client support in your Spring Boot application by adding the @EnableFeignClients annotation.

package com.example.feign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class FeignClientApplication {

    public static void main(String[] args) {
        SpringApplication.run(FeignClientApplication.class, args);
    }
}

Step 3: Define a Feign Client Interface

Define an interface for the HTTP client and use the @FeignClient annotation.

package com.example.feign;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(name = "jsonplaceholder", url = "https://jsonplaceholder.typicode.com")
public interface PostClient {

    @GetMapping("/posts/{id}")
    String getPostById(@PathVariable("id") int id);
}

Step 4: Use the Feign Client

Inject the Feign Client interface and use it to make requests.

package com.example.feign;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class PostController {

    @Autowired
    private PostClient postClient;

    @GetMapping("/post")
    public String getPost() {
        return postClient.getPostById(1);
    }
}

Explanation:

• @FeignClient: Defines a Feign client with a name and base URL.
• @GetMapping: Maps the HTTP GET request to a specific method.
• getPostById: A method in the interface that corresponds to the HTTP GET request.

Comparing WebClient and Feign Client

Feature	WebClient	Feign Client
Programming	Asynchronous and Reactive	Declarative
Use Cases	Modern, reactive applications	Microservices, easy HTTP API calls
Performance	Non-blocking, better performance	Depends on the underlying implementation
Concurrency	Can handle multiple requests simultaneously	Uses Ribbon for client-side load balancing
Integration	Advanced options with streaming	Seamless with Spring Cloud

When to Use WebClient and Feign Client

• 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.

• Feign Client:

  • Use in microservices architectures to simplify HTTP API consumption.
  • When you want to leverage Spring Cloud features like load balancing and circuit breaking.
  • The declarative syntax makes it easier to manage and read.

Conclusion

In this guide, we explored the deprecation of RestTemplate and discussed its alternatives: WebClient and Feign Client. While RestTemplate is simple and easy to use, WebClient offers a modern, non-blocking approach that is better suited for reactive applications. Feign Client provides a declarative approach for working with HTTP APIs, making it ideal for microservices. Understanding these alternatives will help you choose the right tool for your project and leverage the full capabilities of Spring Boot.