How to handle etag if-match in CPI iflow

How to handle etag if-match in CPI iflow?  I searched in blogs and found some blogs in this topic . Today I want demo in the most straight way . I will use the post physical inventory document item as the example.  To post the document item, I need to get the etag for the document item first . Then I use the etag value as If-Match in header of the posting operation . If we don’t put If-Match in posting operation header, the resposne will end with error 428(Precondition Required) .

The following overview of the iflow:

The following is the screen shot of reading physical document item to get etag in header settings

The following is code of putting tag value as header value of If-Match

import com.sap.gateway.ip.core.customdev.util.Message;
import java.util.HashMap;


def Message processData(Message message) {
    
//     //Body
//   Reader reader = message.getBody(Reader);
//   def A_PhysInventoryDocItem = new XmlSlurper().parse(reader) ;
//   def stamp = A_PhysInventoryDocItem.A_PhysInventoryDocItemType.LastChangeDateTime;
//  stamp = "W/\"datetimeoffset"+"'"+stamp+"'\"" ;
//  stamp = stamp.replaceAll(":","%3A");

  def headers = message.getHeaders();
 def stamp = headers.get("etag");

    message.setHeader("If-Match", stamp );
     def body = message.getBody(java.lang.String);
  message.setBody();
      def messageLog = messageLogFactory.getMessageLog(message);
    if (messageLog != null) {
        messageLog.addAttachmentAsString('Iventory Document Item', body, 'application/json');
    }

    return message;
}

The following is screen shot of posting operation with allowing If-Match in header

The end!

Thank you for your time!

Best Regards!

Jacky Liu