code: synchronized public void initSingle() {
  		if (setting == null) {
  			try {
  				setting = new Setting(MONGO_CONFIG_PATH, true);
  			} catch (Exception e) {
  				// 在single模式下，可以没有配置文件。
  			}
  		}
  
  		String group = StrUtil.EMPTY;
  		if (null == this.serverAddress) {
  			//存在唯一分组
  			if (groups != null && groups.length == 1) {
  				group = groups[0];
  			}
  			serverAddress = createServerAddress(group);
  		}
  
  		final MongoCredential credentail = createCredentail(group);
  		try {
  			if (null == credentail) {
  				mongo = new MongoClient(serverAddress, buildMongoClientOptions(group));
  			} else {
  				mongo = new MongoClient(serverAddress, credentail, buildMongoClientOptions(group));
  			}
  		} catch (Exception e) {
  			throw new DbRuntimeException(StrUtil.format("Init MongoDB pool with connection to [{}] error!", serverAddress), e);
  		}
  
  		log.info("Init MongoDB pool with connection to [{}]", serverAddress);
  	}
docs: 初始化<br>
  设定文件中的host和端口有三种形式：
  
  <pre>
  host = host:port
  </pre>
  
  <pre>
  host = host
  port = port
  </pre>
  
  <pre>
  host = host
  </pre>