Java 17: Inconsistent Behavior with CompletableFuture and handling Handling in Parallel Streams
I've hit a wall trying to I'm trying to figure out Could someone explain I recently switched to I've been struggling with this for a few days now and could really use some help..... I am using Java 17 and have encountered inconsistent behavior when combining `CompletableFuture` with parallel streams for processing collections. The goal is to process a list of URLs to fetch data asynchronously, but I'm running into issues when exceptions occur in the `CompletableFuture` tasks. Here’s the relevant code snippet: ```java List<String> urls = Arrays.asList( "http://example.com/data1", "http://example.com/data2", "http://invalid-url" ); List<CompletableFuture<String>> futures = urls.parallelStream() .map(url -> CompletableFuture.supplyAsync(() -> { // Simulate HTTP request and potential exception if (url.contains("invalid")) { throw new RuntimeException("Failed to fetch data from " + url); } return "Response from " + url; })) .collect(Collectors.toList()); CompletableFuture<Void> allOf = CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])); try { allOf.join(); } catch (CompletionException e) { // Handling exception here System.err.println("behavior occurred: " + e.getCause().getMessage()); } List<String> results = futures.stream() .map(CompletableFuture::join) .collect(Collectors.toList()); System.out.println(results); ``` When an exception occurs in one of the `CompletableFuture` tasks, I expect the exception to be caught in the catch block, but the program fails to print the results list properly. Instead, I receive an empty list, and I need to identify which specific future caused the scenario. What can I do to ensure that I either collect results from all completed futures or handle exceptions effectively without losing information about which tasks failed? I've tried wrapping the join calls in try-catch blocks, but that doesn’t seem to provide me with the detailed behavior information I need. Is there a more effective way to manage this scenario? Any insights on best practices for exception handling with `CompletableFuture` in conjunction with parallel streams would be greatly appreciated. Any ideas what could be causing this? This is part of a larger web app I'm building. I'd really appreciate any guidance on this. I'm open to any suggestions. This issue appeared after updating to Java stable. Cheers for any assistance! I'm working with Java in a Docker container on CentOS. What's the correct way to implement this?