connectionPoolSettings = ConnectionPoolSettings.builder()
                                                       .minSize(getMinConnectionsPerHost())
                                                       .maxSize(getConnectionsPerHost())
                                                       .maxWaitQueueSize(getThreadsAllowedToBlockForConnectionMultiplier()
                                                                         * getConnectionsPerHost())
                                                       .maxWaitTime(getMaxWaitTime(), MILLISECONDS)
                                                       .maxConnectionIdleTime(getMaxConnectionIdleTime(), MILLISECONDS)
                                                       .maxConnectionLifeTime(getMaxConnectionLifeTime(), MILLISECONDS)
                                                       .build();

    public static class Builder {
        private String description;
        private String applicationName;
        //读取偏好, 这里默认的是从主节点读取.
        private ReadPreference readPreference = ReadPreference.primary();
        //使用服务器默认的写关注?
        private WriteConcern writeConcern = WriteConcern.ACKNOWLEDGED;
        //使用服务的默认读关注,默认是local
        private ReadConcern readConcern = ReadConcern.DEFAULT;
        private CodecRegistry codecRegistry = MongoClient.getDefaultCodecRegistry();
        private final List<CommandListener> commandListeners = new ArrayList<CommandListener>();
        private final List<ClusterListener> clusterListeners = new ArrayList<ClusterListener>();
        private final List<ServerListener> serverListeners = new ArrayList<ServerListener>();
        private final List<ServerMonitorListener> serverMonitorListeners = new ArrayList<ServerMonitorListener>();
        private int minConnectionsPerHost;
        private int maxConnectionsPerHost = 100;
        private int threadsAllowedToBlockForConnectionMultiplier = 5;
        //设置服务器选择超时（以毫秒为单位），它定义驱动程序在抛出异常之前等待服务器选择成功的时间
        //值为0表示如果没有可用的服务器，它将立即超时。 负值意味着无限期等待
        private int serverSelectionTimeout = 1000 * 30;
        //线程等待连接变为可用的最长时间
        private int maxWaitTime = 1000 * 60 * 2;
        // 线程池中连接的最大空闲时间
        private int maxConnectionIdleTime;
        private int maxConnectionLifeTime;
        //连接超时时间,必须大于0
        private int connectTimeout = 1000 * 10;
        //socket超时时间
        private int socketTimeout = 0;
        //socket是否保活
        private boolean socketKeepAlive = false;
        private boolean sslEnabled = false;
        private boolean sslInvalidHostNameAllowed = false;
        private boolean alwaysUseMBeans = false;
        //设置心跳频率。 这是驱动程序将尝试确定群集中每个服务器的当前状态的频率。 默认值为10,000毫秒
        private int heartbeatFrequency = 10000;
        //设置最小心跳频率。 如果驱动程序必须经常重新检查服务器的可用性，它将至少在上一次检查后等待很长时间，以避免浪费精力。 默认值为500毫秒。
        private int minHeartbeatFrequency = 500;
        //设置用于集群心跳的连接的连接超时
        private int heartbeatConnectTimeout = 20000;
        //设置用于集群心跳的连接的套接字超时
        private int heartbeatSocketTimeout = 20000;
        //本地阈值
        private int localThreshold = 15;
        private String requiredReplicaSetName;
        private DBDecoderFactory dbDecoderFactory = DefaultDBDecoder.FACTORY;
        private DBEncoderFactory dbEncoderFactory = DefaultDBEncoder.FACTORY;
        private SocketFactory socketFactory;
        private boolean cursorFinalizerEnabled = true;
...}