嗨,我正在尝试学习mongo-java driver.i跟随此mongodb documentation.以下是我的代码public class JMongoDBCDemo {MongoClient mongoClient;DB db;DBCollection coll;public JMongoDBCDemo(){MongoClient mongoClient = new MongoClient( "localhost" , 27017 );db = mongoClient.getDB( "messenger" );coll = db.getCollection("users");DBObject myDoc = coll.findOne();System.out.println(myDoc);mongoClient.close();System.ou...