@Override
  public String getRegionServers() {
    ServerManager serverManager = this.master.getServerManager();
    if (serverManager == null) {
      return "";
    }
    return StringUtils.join(serverManager.getOnlineServers().keySet(), ";");
  }
Impl for exposing HMaster Information through JMX
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MetricsMasterWrapperImpl.java