Play framework 2.4（Java）mongo async db驱动程序3.0查询

Question

您好，我正在尝试为MongoDB异步驱动程序（3.0）编写异步代码http://mongo-java-driver/3.0/driver-async/with Play framework2.4(Java)in controller with async result https://www.playframework.com/documentation/2.3.x/javaasync，当我测试它时，承诺的结果是对MongoDB的异步调用之外的，所以有时我的响应中有空的json，请您能帮我一下吗？

public F.Promise<Result> list() {
    final List<Document> accounts = new ArrayList<Document>();
    F.Promise<List<Document>> promiseOfAccounts = F.Promise.promise(
        new F.Function0<List<Document>>() {
            public List<Document> apply() {
                accountRepository.getCollection().find().into(accounts,
                        new SingleResultCallback<List<Document>>() {
                            @Override
                            public void onResult(final List<Document> result, final Throwable t) {
                            }
                        });
                return accounts;
            }
        }
    );
    return promiseOfAccounts.map(
        new F.Function<List<Document>, Result>() {
            public Result apply(List<Document> i) {
                return ok(i);
            }
        }
    );
}

Answer 1

返回accounts时，SigleResultCallback闭包尚未执行。当在OK(i)表达式中序列化时，这将导致列表为空。要使其工作，您必须自己在singleResultCallback中解析承诺。记住Playpromission坐在scalafutures和scala promissions（这与Playf.promissions不同）上。你应该这样做：

Promise<List<Document>> accountsPromise = Promise$.MODULE$.apply();
ArrayList<Document> accounts = new ArrayList<Document>();
accountRepository.getCollection().find().into(accounts,
        new SingleResultCallback<List<Document>>() {
            @Override
            public void onResult(final List<Document> result, final Throwable t) {
                accountsPromise.success(result);
            }
        });
promiseOfAccounts=F.Promise.wrap(accountsPromise.future());
return promiseOfAccounts.map(
        new F.Function<List<Document>, Result>() {
            public Result apply(List<Document> i) {
                return ok(i);
            }
        }
);

当您调用scalapromise的success方法解决时，未来的值变得可用，但您在此之前返回playf.promise时，反应编程的卓越之处就显现出来了。