Calling a REST API in Spring Boot

This tutorial is designed to guide you through the process of calling a REST API using Spring Boot, providing you with practical examples of code along the way. By following this tutorial, you will gain a comprehensive understanding of how to effectively make REST API calls within your Spring Boot applications.

Spring provides the RestTemplate class from the org.springframework.web.client package for handling HTTP requests and interacting with RESTful APIs. RestTemplate, a part of the Spring framework, simplifies the process of making HTTP calls, retrieving data, and sending data to RESTful services.

RestTemplate offers a variety of methods to perform different types of HTTP operations, such as GET, POST, PUT, DELETE, etc. It handles the low-level details of creating and managing HTTP connections, serializing and deserializing request and response bodies, handling request headers, and processing response status codes.

To call a REST API in Spring Boot, you can follow these steps:

1. Create an instance of the RestTemplate class, which allows to make HTTP requests to the API:



RestTemplate restTemplate = new RestTemplate();



2. Prepare the necessary request components for the API request, such as the URL, request headers, and request body (if applicable). You can utilize HttpHeaders and HttpEntity classes for this purpose:



String url = "https://example.com/api/test";

UriComponentsBuilder builder = UriComponentsBuilder.fromUriString(url)
		    .queryParam("param1", "value1")
		    .queryParam("param2", "value2")
		    .queryParam("param3", "value3")
		    .queryParam("param4", "value4");

HttpHeaders headers = new HttpHeaders();
headers.set("Accept", MediaType.APPLICATION_JSON_VALUE);
HttpEntity httpEntity = new HttpEntity<>(headers);



3. Use the RestTemplate instance methods to send the HTTP request to the API endpoint. You can specify the HTTP method (GET, POST, PUT, DELETE, etc.), the URL, the request entity (including headers and body), and the expected response type:



ResponseEntity response = restTemplate.exchange(builder.toUriString(), HttpMethod.GET, httpEntity, String.class);



4. On receiving the API response, you can retrieve the response status code, headers, and body from the ResponseEntity object. You can also perform appropriate error handling based on the response status code or content.
   



if(response.getStatusCode().is2xxSuccessful()) {
   //Handle success response here
   String data = response.getBody();
} else {
   //Handle fail response here
}

That's it! By following these steps, you can successfully call a REST API in Spring Boot using RestTemplate. Remember to handle any exceptions that may occur during the process and to customize the request and response handling based on your specific requirements.