In modern Java applications, consuming REST APIs is a common task, whether it’s fetching data from an external service or interacting with microservices. Spring provides two popular ways to do this: RestTemplate and WebClient.
RestTemplate (Synchronous)
RestTemplate is a traditional, synchronous HTTP client provided by Spring. It blocks the thread until the response is received. While still widely used, it’s considered a bit older and might be replaced by WebClient in reactive applications.
Example:
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RestTemplate restTemplate = new RestTemplate(); String url = "https://api.example.com/data"; ResponseEntity<String> response = restTemplate.getForEntity(url, String.class); System.out.println(response.getBody()); |
- Pros: Simple to use, good for non-reactive (blocking) applications.
- Cons: Not suitable for reactive or high-throughput apps due to thread blocking.
WebClient (Asynchronous & Reactive)
WebClient is part of the Spring WebFlux module. It is non-blocking and designed for reactive applications, but you can also use it in traditional apps.
Example:
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WebClient webClient = WebClient.create(); String url = "https://api.example.com/data"; webClient.get() .uri(url) .retrieve() .bodyToMono(String.class) .subscribe(System.out::println); |
- Pros: Non-blocking, ideal for reactive streams and high-performance systems.
- Cons: Has a steeper learning curve if you’re new to reactive programming.
Use Cases
- Use RestTemplate if you’re building a simple, traditional Spring Boot app without reactive patterns.
- Use WebClient for reactive applications or when you need non-blocking I/O.
