There are several places you can start looking at this:
First,
you should look at the Post entity class. This will probably have to be modified to include your new properties.
To manage setting and storing this new property, you will need to look at the methods that handle processing the post form(s). These are: PostAction.insertSave() and PostAction.editSave().
To make the information in the POJO entity object persistent, you will have to make a custom PostDAO implimentation. This will have to handle saving and loading the information from/to the DB table/column.
As to displaying the extra information, once it is part of the Post object, the templates can just use it as needed.
[originally posted on jforum.net by monroe]