code: public static String getApplicationPropertiesConfigFilter(String applicationPid) {
          String applicationConfigFilter = null;
  
          StringBuilder applicationFilter = new StringBuilder(200);
          applicationFilter.append("(&");
          applicationFilter.append(FilterUtils.createPropertyFilter(CFG_SERVICE_FACTORY_PID, CFG_APP_PROPERTIES));
          applicationFilter.append(FilterUtils.createPropertyFilter(CFG_CONFIG_PARENT_PID, applicationPid));
          applicationFilter.append(')');
  
          applicationConfigFilter = applicationFilter.toString();
  
          return applicationConfigFilter;
      }
docs: Get the filter string which will extract <appProperties> elements for the given application
  
  @param applicationPid The pid of the application in the config
  @return A filter string to be used by the OSGi ConfigurationAdmin service