@Nullable
  private Expression getSelectorExpression(MessageHeaders headers) {
    Expression expression = null;
    if (getSelectorHeaderName() != null) {
      String selector = SimpMessageHeaderAccessor.getFirstNativeHeader(getSelectorHeaderName(), headers);
      if (selector != null) {
        try {
          expression = this.expressionParser.parseExpression(selector);
          this.selectorHeaderInUse = true;
          if (logger.isTraceEnabled()) {
            logger.trace("Subscription selector: [" + selector + "]");
          }
        }
        catch (Throwable ex) {
          if (logger.isDebugEnabled()) {
            logger.debug("Failed to parse selector: " + selector, ex);
          }
        }
      }
    }
    return expression;
  }
Return the name for the selector header.
@since 4.2
ambari-server/src/main/java/org/apache/ambari/server/agent/stomp/AmbariSubscriptionRegistry.java