public boolean hasDurableClient(String durableId) {
    for (CacheClientProxy proxy : _clientProxies.values()) {
      ClientProxyMembershipID proxyID = proxy.getProxyID();
      if (durableId.equals(proxyID.getDurableId())) {
        return true;
      }
    }
    return false;
  }
Checks if there is any proxy present for the given durable client

@param durableId - id for the durable-client
@return - true if a proxy is present for the given durable client

@since GemFire 5.6
geode-core/src/main/java/org/apache/geode/internal/cache/tier/sockets/CacheClientNotifier.java