mongodb打开连接问题

我的 mongo 控制台中有以下日志：

Tue Jul 23 17:20:01.301 [initandlisten] waiting for connections on port 27017
Tue Jul 23 17:20:01.401 [websvr] admin web console waiting for connections on port 28017
Tue Jul 23 17:20:01.569 [initandlisten] connection accepted from 127.0.0.1:58090 #1 (1 connection now open)
Tue Jul 23 17:20:01.570 [initandlisten] connection accepted from 127.0.0.1:58089 #2 (2 connections now open)
Tue Jul 23 17:20:21.799 [initandlisten] connection accepted from 127.0.0.1:58113 #3 (3 connections now open)
....
....
....

同样，日志继续，现在是 112。每次我启动 mongo 服务器时都会发生这种情况。我的代码中只有一个单例连接。这里可能出现什么问题：

public static DB getConnection(String databaseName) throws AppConnectionException {

    if (null != db) {
        Logger.debug("Returning existing db connection...!");
        return db;
    }

    Logger.debug("Creating new db connection...!");
    final String connStr = PropertyRetreiver.getPropertyFromConfigurationFile("rawdata.url");

    try {

        final MongoClientURI uri = new MongoClientURI(connStr);
        final MongoClient client = new MongoClient(uri);
        db = client.getDB(databaseName);

    } catch (UnknownHostException e) {
        throw new AppConnectionException(
                "Unable to connect to the given host / port.");
    }

    return db;
}

MongoClient有内部连接池。可以配置最大连接数（默认为 100）。您可以通过使用来设置它MongoClientOptions像这样：

MongoClientOptions options = MongoClientOptions.builder()
                .connectionsPerHost(100)
                .autoConnectRetry(true)
                .build();

然后将这些选项提供给MongoClient（在Mongo Java API v2.11.1中检查过）。 池中的连接保持打开状态（打开和关闭连接通常是一项昂贵的操作），以便以后可以重用它们。

我还将使用重构您的 MongoDB 客户端单例enum例如为了避免放置synchronized就这个方法。

这是我的意思的草图：

public enum MongoDB {
    INSTANCE;

    private static final String MONGO_DB_HOST = "some.mongohost.com";
    private Mongo mongo;
    private DB someDB;

    MongoDB() {

        MongoClientOptions options = MongoClientOptions.builder()
                .connectionsPerHost(100)
                .autoConnectRetry(true)
                .readPreference(ReadPreference.secondaryPreferred())
                .build();

        try {
            mongo = new MongoClient(MONGO_DB_HOST, options);
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }

        someDB = mongo.getDB("someDB");
         //authenticate if needed
         //boolean auth = someDB.authenticate("username", "password".toCharArray());
         //if(!auth){
         //     System.out.println("Error Connecting To DB");
         //}        
    }

    public DB getSomeDB() {
        return someDB;
    }

    //call it on your shutdown hook for example 
    public void close(){
        mongo.close();
    }
}

然后，您可以通过以下方式访问您的数据库

MongoDB.INSTANCE.getSomeDB().getCollection("someCollection").count();