[Struts2+tiles] How can I make title dynamically?

Question

I'm developing BBS in struts2 and tiles(2) framework.

I want to push a value in ActionSupport class and pop the value in layout.jsp of tiles. but i just keep failing to access to the value.

I will explain my works step by step.

1) Users click a link to view an article at list page. And BoardView class will be called as defined in struts.xml

--list.jsp--
<a href="view_board?num=${num}"> ${ subject } </a>

--struts.xml--
<action name="View_board" class="board.BoardView">
<result type="tiles">board.view</result>
</action>

2)Action class will put title into the value stack... right?

--BoardView class--

 
public class BoardView extends ActionSupport

    private String title;

    public void Execute() throws Exception {
        ...  
        setTitle(board.getSubject());
        return SUCCESS; 
    }
    ...  
    (setter and getter of title)  

3) As ActionClass returns SUCCESS, it will go to tiles definition named board.view
--struts.xml--
<action name="View_board" class="board.BoardView">
<result type="tiles">board.view</result>
</action>

4)Here's the tiles-def.xml and the problem. I think the value of 'title' can't be popped from value stack.
==tiles-def.xml==
<definition name="board.view" extends="layout">
<put-attribute name="title" value="%title" />
<put-attribute name="body" value="/board/view.jsp" />
</definition>
(I can't indent with tags... sorry)
Here's the layout.jsp ==layout.jsp==
... <title><tiles:getAsString name="title" /></title> ...

I tried to replace the value attribute to %{title}, $title and ${title}. But nothings worked out. Web Browser just shows the string itself($title).

I don't know what to do... please help me.

I hope you all understand my works despite my bad explanation.