使用Java检索MongoDb嵌套文档的所有键

import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

import java.util.HashSet;
import java.util.Set;

public class MongoDBUtils {

    public static Set<String> getAllKeys(MongoCollection<Document> collection) {
        Set<String> keys = new HashSet<>();
        for (Document document : collection.find()) {
            getAllKeysRecursive(document, keys);
        }
        return keys;
    }

    private static void getAllKeysRecursive(Document document, Set<String> keys) {
        for (String key : document.keySet()) {
            keys.add(key);
            Object value = document.get(key);
            if (value instanceof Document) {
                getAllKeysRecursive((Document) value, keys);
            }
        }
    }

    public static void main(String[] args) {
        MongoClient mongoClient = new MongoClient("localhost", 27017);
        MongoDatabase database = mongoClient.getDatabase("mydb");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        Set<String> keys = getAllKeys(collection);
        for (String key : keys) {
            System.out.println(key);
        }

        mongoClient.close();
    }
}