[SalesForce] Retrieve UserId of @mention user from chatter post in Apex

Chatter in apex (ConnectApi) was designed for this type of coding:

ConnectApi.FeedType feedType = ConnectApi.FeedType.UserProfile;

ConnectApi.FeedItemInput input = new ConnectApi.FeedItemInput();
ConnectApi.MessageBodyInput messageInput = new ConnectApi.MessageBodyInput();
ConnectApi.TextSegmentInput textSegment;
ConnectApi.MentionSegmentInput mentionSegment = new ConnectApi.MentionSegmentInput();

messageInput.messageSegments = new List<ConnectApi.MessageSegmentInput>();

textSegment = new ConnectApi.TextSegmentInput();
textSegment.text = 'Hey there ';
messageInput.messageSegments.add(textSegment);

mentionSegment.id = '005D0000001LLO1';
messageInput.messageSegments.add(mentionSegment);

textSegment = new ConnectApi.TextSegmentInput();
textSegment.text = '. How are you?';
messageInput.messageSegments.add(textSegment);

input.body = messageInput;

ConnectApi.FeedItem feedItemRep = ConnectApi.ChatterFeeds.postFeedItem(communityId, feedType, 'me', input, null);

In this case the mentionSegment.id would be your group id. Full documentation of the ConnectApi can be found here:

http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_classes_connect_api.htm

The only way to @mention someone in apex is using the ConnectApi (AKA Chatter in apex) and not by just creating a FeedItem in apex. You'll need to refactor most everything in your code around the posting to Chatter. Here is a code sample of a text post with a mention borrowed from an example that Jeff Douglas has on his blog:

// makes a simple chatter text post to the specified user from the running user 
public static void mentionTextPost(Id userId, Id userToMentionId, String postText) { 

   ConnectApi.MessageBodyInput messageInput = new ConnectApi.MessageBodyInput();
   messageInput.messageSegments = new List();

   // add some text before the mention
   ConnectApi.TextSegmentInput textSegment = new ConnectApi.TextSegmentInput();
   textSegment.text = 'Hey ';
   messageInput.messageSegments.add(textSegment);

   // add the mention
   ConnectApi.MentionSegmentInput mentionSegment = new ConnectApi.MentionSegmentInput();
   mentionSegment.id = userToMentionId;
   messageInput.messageSegments.add(mentionSegment);

   // add the text that was passed
   textSegment = new ConnectApi.TextSegmentInput();
   textSegment.text = postText;
   messageInput.messageSegments.add(textSegment);

   ConnectApi.FeedItemInput input = new ConnectApi.FeedItemInput();
   input.body = messageInput;

   // post it
   ConnectApi.ChatterFeeds.postFeedItem(null, ConnectApi.FeedType.UserProfile, userId, input, null);

}  

Lastly, it's worth noting that you can only post as the running user. It's not possible to post on anyone else's behalf.

• With credit to Jeff, posted on his blog here, Chatter for Apex Code Examples