使用 Java 获取集合中所有键名称的名称 [英] Get names of all keys name in collection using Java

问题描述

在这个集合中(称为播放")

In this collection (called "play")

{ "_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?

How can I retrieve the names of the keys using Java?

示例输出:

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

目前的代码是这样的

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...
     */   
    }
}

推荐答案

如果你在 API 中查看 DBCursor.next()，它返回一个DBObject，它是 BSONObject 带有 keySet() 方法.该字段是一个Set，带有描述

If you look in the API at DBCursor.next(), it returns a DBObject, which is a subtype of BSONObject with a keySet() method. That field is a Set<String>, with the description

该对象中字段的名称

因此，您可能可以使用

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

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