[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);

        /**
         * 
         * WHEN EXCEPTION IN setErrorResult, Spring WILL TRIGGER THE Spring Exception Handler AS YOU KNOW IT (I HOPE)
         * SO, YOU COULD HOOK UP THE HANDLER AND RETURN YOUR CUSTOM MESSAGESS (as usual)
         * 
         */
        
        // 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 */

        
        @FunctionalInterface
        public interface DeferredCall<T> {
                
                public T doCall();
        }
        
        public static final <T> DeferredResult<T> deferredAdapter(CompletableFuture<T> completableFuture) {
                
        DeferredResult<T> deferredResult = new DeferredResult<>(ASYNC_TIMEOUT);

        completableFuture
                .thenAcceptAsync(deferredResult::setResult)
                .exceptionally(exception -> {
                                
                                LOGGER.error("error: ", exception);
                                
                                deferredResult.setErrorResult(exception);
                                
                                return null;
                        });
        
        return deferredResult;  
        }
        
}