完成多个异步查询后运行查询

Question

我在这段代码中使用了vertx mongoclient：

mongoClient.getCollections(res -> {
        if (res.succeeded()) {
            if (res.result().size() > 0) {
                for (String collection : res.result()) {
                    mongoClient.dropCollection(collection, resDrop -> {
                        if (resDrop.succeeded()) {
                            LOGGER.warn(collection + "was dropped");
                        }
                    });
                }
            } else LOGGER.warn("database was dropped");
        } else LOGGER.warn("database was dropped");
    });

我想在删除所有旧收藏后创建一些新收藏品 但正如我们所知，删除异步执行的集合 我如何知道所有旧收藏品何时被删除？

Answer 1

这是一个常见的asynchronous coordination问题。请查看Vert.x文档中的Concurrent composition部分。

Answer 2

mongoClient.getCollections(res -> {
        if (res.succeeded()) {
            if (res.result().size() > 0) {
                **List<Future> futureList  = new ArrayList<>();** 
                for (String collection : res.result()) {
                    mongoClient.dropCollection(collection, resDrop -> {
                        if (resDrop.succeeded()) {
                            **Future future = Future.future();
                            futureList.add(future);
                            future.complete();**
                            LOGGER.warn(collection + "was dropped");
                        }else{
                          future.fail(ar.cause());  
                       }

                    });
                }

               **CompositeFuture.all(futureList).setHandler(ar -> {
                    if (ar.succeeded()) {
                        LOGGER.info("All collections was dropped");
                    } else {
                        LOGGER.warn("One or all collections was not dropped");
                    }
                });**
            } else LOGGER.warn("database was dropped");
        } else LOGGER.warn("database was dropped");
    });

Answer 3

我建议使用CompletableFutures。您可以调用allOf方法。