Struts 2 passing data from JSP to action class

Question

I'm trying to understand somebody's else Struts 2 code and I'm stuck with a data passing problem.

I know that on a JSP page, if you use a <s:textfield name="something" ... /> tag, than struts2 will try to call setSomething(...) automatically in the action class.

I'm now seeing this type of code:

<s:textfield name="item.name" ... />

and I'm wondering, how does this . (dot) work? I have a method called setItem() in my action class, and the object that is being set in that method has a setName() method, but apparently this doesn't work. What does the dot mean between item and name and how do I use it correctly to instantiate the item and set it's name?

PS: The item object that is being set in setItem() in my action class has an empty args constructor.

Answer 1

The problem is solved. The getItem() actually contained the following code:

public Item getItem()
{
    System.out.println("Trying to get item: " + item.toString());
    return item;
}

And this gave a nullpointer exception because item was null. Only, this nullpointerexception was NOT THROWN by the struts framework! The code just continued (and failed of course...). When I removed the sysout statement, the code worked.

Answer 2

In OGNL . is the dot notation.

item.name means getItem().setName();
item.subitem.name means getItem().getSubitem.setName();

One problem could be the missing empty args constructor, as described here, but you are saying it's not your case; then I bet on the "missing getter for Item". If it's not, please post more relevant code.

Answer 3

Make sure there is public method for getItem().setName()

Maybe the methods are not available or not public or a typo, for example getitem() instead of getItem().

Your action should have setItem(Item item)

Answer 4

Struts2 treated value in the name attribute "item.name" like OGNL expression. But it doesn't substitute the result of evaluation to the name attribute but to the value attribute if it didn't set. Then if you submit the form the parameter from the name attribute is created and sent via HTTP request. Struts2 used params interceptor to parse parameter names. It treated such names like OGNL expression and call appropriate methods get and set while accessing objects and setting values. Dot in OGNL expression stands for property resolver. In your case you should have getItem() method to set the value and this item should return not null value. setItem() is not used there. May be you ask why it's not used, but it would probably another question.