How to add and remove subscriber in a same Operation particpant?

at the time the participant is called, the workitem as been saved already.

so you will have to add the user as a subscriber, and save the workitem again,  which will call the participant again (so you need to set some flag to know this)
then you need to remove them as a subscriber, and save the workitem AGAIN.. which will call the participant again.

of course, I do not know if this will cause an email to be queued to send, as I don't know the internal timing of the calls.

Thanks Sam.
I did the exact thing. I used SaveWorkitem3 method to send the additional parameter to avoid recursion.

But the thing is that the subscription is not happening. I removed the code for remove the subscriber and checked. user is not added as the Subscriber.

I am having the User ID as string. So I tried the following but no luck

sourceWorkItem = (IWorkItem) workItemServer.getAuditableCommon().resolveAuditable(sourceWorkItem ,IWorkItem.FULL_PROFILE,monitor).getWorkingCopy();
IContributor userIAG = (IContributor) IContributor.ITEM_TYPE.createItem();
userIAG.setUserId("myuserid");
ISubscriptions subscription= sourceWorkItem.getSubscriptions();
subscription.add(userIAG);
workItemServer.saveWorkItem3(sourceWorkItem, sourceWIRef, null, additionalParams);

   

                       

IContributor userIAG = (IContributor) IContributor.ITEM_TYPE.createItem();
userIAG.setUserId("myuserid");

and adding that contributor to the subscriber.

U are creating a user entry in memory, not looking a user up in the system.

u need to use the IContributorManager class to find the user entry, from the javadoc

IContributorRecord

fetchContributorRecordByUserId(IContributorUserId userId, org.eclipse.core.runtime.IProgressMonitor monitor)           Fetches a contributor record by one of its user ids.

Sam,

Thanks for guiding me in right direction.
As I am using the Server side plugin, I have achieved the functionality using

IContributorService#fetchContributorByUserId.