reta opened a new pull request #526: CXF-7989: org.apache.cxf.jaxrs.JAXRSInvoker should handle CompletionException URL: https://github.com/apache/cxf/pull/526 The Problem === In case when CXF is used along with `CompletionStage` / `CompletableFuture`, in most cases the error handling is propagated back through `CompletionException` instance (http://cs.oswego.edu/pipermail/concurrency-interest/2014-August/012911.html). It works but it forces users to introduce own implementations of `ExceptionMapper`s and manually unwrap the `CompletionException` into something more meaningful. Use cases === There are 3 leading use cases which cover most typical usage of the `CompletionStage` / `CompletableFuture`. 1. `@Suspended AsyncResponse` ``` public void get(@PathParam("isbn") String isbn, @Suspended final AsyncResponse resp) { client.target("http://localhost:19092/services/catalog/"; + isbn) .request() .rx() .get(Book.class) .whenComplete((r, ex) -> { if (ex != null) { resp.resume(ex); } else { resp.resume(r); } }); } ``` 2. Return `CompletableFuture<Book>` ``` public CompletableFuture<Book> get(@PathParam("isbn") String isbn) { return client .target("http://localhost:19092/services/catalog/"; + isbn) .request() .rx() .get(Book.class) .toCompletableFuture(); } ``` 3. Return constructed instance of the `CompletableFuture<Book>` ``` public CompletableFuture<Book> get(@PathParam("isbn") String isbn) { final CompletableFuture<Book> future = new CompletableFuture<Book>(); future.completeExceptionally(...); return future; } ``` Suggested Solution === Instrument `JAXRSInvoker::handleAsyncResponse` to distinguish `CompletionException`, unwrap the cause and use it to select the appropriate `ExceptionMapper` (if any). @rmannibucau why `JAXRSInvoker::handleAsyncResponse` and not `JAXRSInvoker::checkFutureResponse`, the 1st use case which uses suspended async response does not flow through `JAXRSInvoker::checkFutureResponse` but all three use cases run through `JAXRSInvoker::handleAsyncResponse` @coheigea @dkulp guys would really appreciate if you could take a quick look, small change but may introduce undesired side effects, thanks a lot.
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