从Mongo查询格式到java的投影

db.collection.find(
   <query>,
   <projection>
)

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

public class MongoDBExample {
    public static void main(String[] args) {
        // 连接MongoDB数据库
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        // 选择数据库
        MongoDatabase database = mongoClient.getDatabase("mydb");
        // 选择集合
        MongoCollection<Document> collection = database.getCollection("mycollection");

        // 构建查询条件
        Document query = new Document("name", "John");
        // 构建投影
        Document projection = new Document("name", 1).append("age", 1);

        // 执行查询操作
        MongoCursor<Document> cursor = collection.find(query).projection(projection).iterator();
        while (cursor.hasNext()) {
            Document document = cursor.next();
            System.out.println(document.toJson());
        }

        // 关闭连接
        mongoClient.close();
    }
}