我正在尝试检索mongo集合中所有文档和嵌入文档的所有字段。这是一个文档的示例：

{
   "_id": {
      "$oid": "53b309def468718462e0c390"
   },
   "customer": {
      "companyName": "Vins et alcools Chevalier",
      "contactName": "Paul Henriot",
   },
   "employee": {
      "employeeId": 5,
      "firstName": "Steven",
      "lastName": "Buchanan"
   },
   "orderItems": [
      {
         "productName": "Queso Cabrales",
         "unitPrice": 14,
         "quantity": 12
      },
      {
         "productName": "Singaporean Hokkien Fried Mee",
         "unitPrice": 9.8,
         "quantity": 10
      }
   ],
   "orderId": 10248,
   "orderDate": {
      "$date": "1996-07-04T07:00:00.000Z"
   },
   "requiredDate": {
      "$date": "1996-08-01T07:00:00.000Z"
   },
   "shippedDate": {
      "$date": "1996-07-16T07:00:00.000Z"
   },
   "shipVia": "Federal Shipping",
   "freightCost": 32.38
}

以下是我的代码和输出：

MongoCursor<Document> cursor;
MongoCollection<Document> collection = database.getCollection("test");
cursor = collection.find().iterator();
try {
    while (cursor.hasNext()) {
         //System.out.println(cursor.next().toJson());
         System.out.println(cursor.next().get("key"));
    }       
} finally {
    cursor.close();
}

这就是输出：

null null null null null ...

我只想要名字部分，但没用。
我在mongodbv4.2中使用java驱动程序3.12.4
给你加油。