Java 11: implementing CompletableFuture Not Completing in Asynchronous REST Calls
I'm a bit lost with I tried several approaches but none seem to work. I'm working with a frustrating scenario with `CompletableFuture` in my Java 11 Spring Boot application. I'm making asynchronous REST calls, but sometimes the futures just seem to hang and never complete. I have the following method that makes multiple asynchronous calls to a third-party API: ```java import java.util.concurrent.CompletableFuture; import org.springframework.web.client.RestTemplate; public class ApiService { private final RestTemplate restTemplate; public ApiService(RestTemplate restTemplate) { this.restTemplate = restTemplate; } public CompletableFuture<String> fetchDataAsync(String url) { return CompletableFuture.supplyAsync(() -> restTemplate.getForObject(url, String.class)); } public CompletableFuture<String> fetchAllData() { CompletableFuture<String> call1 = fetchDataAsync("https://api.example.com/data1"); CompletableFuture<String> call2 = fetchDataAsync("https://api.example.com/data2"); return CompletableFuture.allOf(call1, call2) .thenApply(v -> call1.join() + call2.join()); } } ``` When I call `fetchAllData()`, the futures for `call1` and `call2` sometimes complete successfully, but other times, I just end up waiting indefinitely. I’ve added logging to check if the requests are being made and if responses are coming back, and everything seems fine when it works. I've tried setting a timeout on the `CompletableFuture` using `completeOnTimeout`, but it doesn't seem to help as the futures are still hanging. Here’s how I attempted to implement the timeout: ```java public CompletableFuture<String> fetchAllDataWithTimeout() { CompletableFuture<String> futureData = fetchAllData().completeOnTimeout("Timeout occurred", 5, TimeUnit.SECONDS); return futureData; } ``` However, I still need to identify the root cause for these hang-ups. Could there be issues related to thread pooling or something in the `RestTemplate` configuration that I’m missing? Any insight or suggestions would be greatly appreciated, especially on debugging this behavior or ensuring the futures complete reliably. For context: I'm using Java on Linux. Any help would be greatly appreciated! I've been using Java for about a year now. Thanks for your help in advance!