java - Java + MongoDB：不必要的连接

Question

创建了一个单例类来维护 MongoDB，但每次初始化时它仍然会创建一个新连接。

public class MongoDB {

private static MongoDB ourInstance = null;
private DB db;
private MongoClient mongoClient;


public MongoDB() throws UnknownHostException {
    try{
        // To directly connect to a single MongoDB server (note that this will not auto-discover the primary even
        // if it's a member of a replica set:
        mongoClient = new MongoClient( "localhost" , 27017 );
        db = mongoClient.getDB( "roam" );
    }
    catch (UnknownHostException e){
        System.out.println("Could not establish database connection");
    }
}

public DBCursor setCursor (String collectionName, BasicDBObject query, BasicDBObject field){
    return db.getCollection(collectionName).find(query, field);
}



public static synchronized MongoDB getInstance() {
    if (ourInstance == null) {
        try {ourInstance = new MongoDB();}
        catch (Exception e) {throw new ExceptionInInitializerError(e);}
    }
    return ourInstance;
}

protected void finalize (){
   this.mongoClient.close();
}

}

当我创建一个 Web 应用程序时，它会在每次刷新带有数据库引用的页面时创建一个新连接。