What approaches can be used to improve the efficiency of a service that performs four independent HTTP requests to different systems simultaneously?

To improve the efficiency of a service that makes four independent HTTP requests to different systems, the following approaches can be applied:

1. Parallel execution of requests — use multithreading or asynchronous calls so that requests are executed simultaneously rather than sequentially. In Java, you can use CompletableFuture or libraries like RxJava.

2. Connection Pooling — use an HTTP connection pool to avoid the overhead of establishing a connection for each request.

3. Caching responses — if responses do not change often, cache the results to avoid making repeated requests.

4. Timeout and retry optimization — set reasonable timeouts and retry logic to prevent delays caused by slow or unavailable services.

Example using CompletableFuture:

import java.net.http.*;
import java.net.URI;
import java.util.concurrent.*;

HttpClient client = HttpClient.newHttpClient();

CompletableFuture<HttpResponse<String>> req1 = client.sendAsync(
    HttpRequest.newBuilder(URI.create("http://service1/api")).build(),
    HttpResponse.BodyHandlers.ofString());
CompletableFuture<HttpResponse<String>> req2 = client.sendAsync(
    HttpRequest.newBuilder(URI.create("http://service2/api")).build(),
    HttpResponse.BodyHandlers.ofString());
// Similarly for req3 and req4

CompletableFuture.allOf(req1, req2 /*, req3, req4 */).join();

// Process results after all requests are completed
String response1 = req1.get().body();
String response2 = req2.get().body();
// ...