java - 在一个应用程序中哪个应该是单例？ MongoClient 或 MongoDatabase 或 MongoCollection？

Question

如文档中所述: http://mongodb.github.io/mongo-java-driver/3.3/driver/getting-started/quick-tour/

The MongoClient instance actually represents a pool of connections to the database; you will only need one instance of class MongoClient even with multiple threads.

使用下面的代码可以获得集合(就像RDMS中的'table'):

MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection<Document> collection = database.getCollection("test");

我发现这些代码总是返回新实例，那么，在我的应用程序中将 MongoDatabase 或 MongoCollection 作为单例怎么样？

Answer 1

MongoClient 通常应该是单例。你的报价提到了这一点

The MongoClient instance actually represents a pool of connections to the database; you will only need one instance of class MongoClient even with multiple threads.

它还在 javadocs 中提到了这一点:

A MongoDB client with internal connection pooling. For most applications, you should have one MongoClient instance for the entire JVM.

主要将 MongoDatabase 或 MongoCollection 作为单例(还有其他原因)是没有意义的，因为底层连接可能会失效，这需要一些编码来刷新单例 MongoDatabase 或单例 MongoCollection。