plz tell mewhat to add for the return statement

What do you mean by "what to add"? Why would you want to change that method? You would call it, not change it.

attachment dao cannot be resolved or not in the field this is the error

Don't copy that method to the ForumAction class, use it as is, like new AttachmentCommon(request, forumId).getAttachments(postId, forumId). The postId and forumId variables need to reflect the post that has the attachment you intend to show. request is available as an instance variable in the ForumAction class.

suggest me how to include the source code in the generated war file

What would be the purpose of that? The Maven war plugin can probably do that, so you might want to read up on that.