[Spring MVC] Callable vs DeferredResult

from Understanding Callable and Spring DeferredResult

Callable

Callable: java.util.concurrent.Callable

@RestController
public class AsyncCallableController {
    private final Logger logger = LoggerFactory.getLogger(this.getClass());
    private final TaskService taskService;

    @Autowired
    public AsyncCallableController(TaskService taskService) {
        this.taskService = taskService;
    }

    @RequestMapping(value = "/callable", method = RequestMethod.GET, produces = "text/html")
    public Callable<String> executeSlowTask() {
        logger.info("Request received");
        Callable<String> callable = taskService::execute;
        logger.info("Servlet thread released");

        return callable;
    }
}

2015-07-12 13:07:07.012  [nio-8080-exec-5] x.s.w.c.AsyncCallableController          : Request received
2015-07-12 13:07:07.013  [nio-8080-exec-5] x.s.w.c.AsyncCallableController          : Servlet thread released
2015-07-12 13:07:12.014  [      MvcAsync2] x.spring.web.service.TaskServiceImpl     : Slow task executed

controller可以return Callable物件達到非同步的效果
Spring MVC之後會管理TaskExecutor使用不同的thread來執行這個Callable物件的task

DeferredResult

DeferredResult: org.springframework.web.context.request.async.DeferredResult<T>

@RestController
public class AsyncDeferredController {
    private final Logger logger = LoggerFactory.getLogger(this.getClass());
    private final TaskService taskService;

    @Autowired
    public AsyncDeferredController(TaskService taskService) {
        this.taskService = taskService;
    }

    @RequestMapping(value = "/deferred", method = RequestMethod.GET, produces = "text/html")
    public DeferredResult<String> executeSlowTask() {
        logger.info("Request received");
        DeferredResult<String> deferredResult = new DeferredResult<>();
        CompletableFuture.supplyAsync(taskService::execute)
            .whenCompleteAsync((result, throwable) -> deferredResult.setResult(result));
        logger.info("Servlet thread released");

        return deferredResult;
    }
}

2015-07-12 13:28:08.433  [io-8080-exec-10] x.s.w.c.AsyncDeferredController          : Request received
2015-07-12 13:28:08.475  [io-8080-exec-10] x.s.w.c.AsyncDeferredController          : Servlet thread released
2015-07-12 13:28:13.469  [onPool-worker-1] x.spring.web.service.TaskServiceImpl     : Slow task executed 

controller也可以return DeferredResult物件達到非同步的效果
但跟Callable不同的是並非由Spring MVC管理
由上例是由CompletableFuture管理使用supplyAsync方法
在ForkJoinPool.commonPool()取得thread執行task後再給DeferredResult物件setResult

其他也可以由JMS或AMQP的message來管理¹

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