异步请求 使用副线程处理 请求，主线程可以做其他事情，提高吞吐量

@RestController
public class AsyncController {
    private Logger logger = LoggerFactory.getLogger(getClass());
    
    @RequestMapping("/order")
    public DeferredResult<String> order() throws Exception {
        logger.info("主线程开始");
        
        Callable<String> result = new Callable<String>() {
            @Override
            public String call() throws Exception {
                logger.info("副线程开始");
                Thread.sleep(1000);
                logger.info("副线程返回");
                return "success";
            }
        };
        return result;
    }

}