Question

在此集合中（称为“播放”）

{ "_id" : 0 , "outlook" : "sunny" , "temp" : "hot" , "humidity" : "high" , "windy" : "weak" , "lable" : "no"}
{ "_id" : 1 , "outlook" : "sunny" , "temp" : "hot" , "humidity" : "high" , "windy" : "strong" , "lable" : "no"}
{ "_id" : 2 , "outlook" : "overcast" , "temp" : "hot" , "humidity" : "high" , "windy" : "weak" , "lable" : "yes"}
{ "_id" : 3 , "outlook" : "rain" , "temp" : "mild" , "humidity" : "high" , "windy" : "weak" , "lable" : "yes"}
{ "_id" : 4 , "outlook" : "rain" , "temp" : "cool" , "humidity" : "normal" , "windy" : "weak" , "lable" : "yes"}
{ "_id" : 5 , "outlook" : "rain" , "temp" : "cool" , "humidity" : "normal" , "windy" : "strong" , "lable" : "no"}

如何使用Java检索密钥的名称？

示例输出：

[ "_id" , "outlook" , "temp" , "humidity" , "windy" , "lable" ]

到目前为止，代码看起来像这样

public class test {
    public static void main(String[] args) {
        DB dbtest = connection.dbconn();
        DBCollection collection = dbtest.getCollection("play");
        BasicDBObject allQuery = new BasicDBObject();;

        DBCursor cursor = collection.find(allQuery);
        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }

     /**
       write code.. here...
     */   
    }
}

Answer 1

如果您在DBCursor.next()处查看API，则会返回DBObject，这是BSONObject with a keySet()方法的子类型。该字段为Set<String>，其描述为

此对象中字段的名称

因此，您可以使用

for (String key: cursor.next().keySet()) {
    // do whatever with the key name here, f.ex.
    System.out.println(key);
}

使用Java获取集合中所有键名的名称

1 个答案: