import org.apache.hadoop.yarn.client.RMHAServiceTarget; //导入依赖的package包/类
@Override
protected HAServiceTarget resolveTarget(String rmId) {
  Collection<String> rmIds = HAUtil.getRMHAIds(getConf());
  if (!rmIds.contains(rmId)) {
    StringBuilder msg = new StringBuilder();
    msg.append(rmId + " is not a valid serviceId. It should be one of ");
    for (String id : rmIds) {
      msg.append(id + " ");
    }
    throw new IllegalArgumentException(msg.toString());
  }
  try {
    YarnConfiguration conf = new YarnConfiguration(getConf());
    conf.set(YarnConfiguration.RM_HA_ID, rmId);
    return new RMHAServiceTarget(conf);
  } catch (IllegalArgumentException iae) {
    throw new YarnRuntimeException("Could not connect to " + rmId +
        "; the configuration for it might be missing");
  } catch (IOException ioe) {
    throw new YarnRuntimeException(
        "Could not connect to RM HA Admin for node " + rmId);
  }
}