[JavaForFun] /

package de.spring.webservices.rest.controller.adapters;

import java.util.concurrent.CompletableFuture;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.context.request.async.DeferredResult;

public class CompletableFutureAdapter {
        private static final Logger LOGGER = LoggerFactory.getLogger(CompletableFutureAdapter.class);

        // With no value, we depend on the Tomcat/Jboss/Jetty/etc timeout value for asynchronous requests.
        // Spring will answer after 60 secs with an empty response (by default) and HTTP 503 status (by default) when timeout.
        private static final long ASYNC_TIMEOUT = 60000;  /* milliseconds */
        
        
        public static final <T> DeferredResult<T> deferredAdapter(CompletableFuture<T> completableFuture) {

        DeferredResult<T> deferredResult = new DeferredResult<>(ASYNC_TIMEOUT);

        completableFuture
                .thenAcceptAsync(deferredResult::setResult)
                .exceptionally(exception -> {
                        Throwable realException = launderException(exception);

                                LOGGER.error("error: ", realException);

                                deferredResult.setErrorResult(exception);
                                return null;
                        });

        return deferredResult;  
        }
        
        private static final Throwable launderException(Throwable exception) {
                return exception.getCause() != null
                           ? exception.getCause()
                           : exception;
        }
}