Why i have to specify the parameters (property and name) in both tags?

Question

Recently i learned how to populate a html:select with data from a DB table with a int value and a String value (value and label of an option). For that i create a business object that represent one pair value&label (i called categoryBO) and another business object that contains a list of the business objects categoryBO. So in my JSP i have the next code:
<html:select name="lista" property="listaPropiedades">
<html:optionsCollection name="lista" property="listaPropiedades" value="varValor" label="varLabel" />
</html:select> Well i understand the next: name is the name of the business object that contains the list with the objects that represents the options in the select tag; property is the name of the list object, in the business object i need to have the getters and setters for that list; then value is the name of the variable that contains the data that will be the value of each option and label is the name of the variable that contains the data that will be the value of each label.
But i have the next questions:
1. Why i have to establish the parameters property and name for bot html:select and html:optionsCollection? Why not only in html:select or only html:optionsCollection?
2. In the ActionForm for my JSP i don�t know what data type have to use to declare the variable that's linked with the option or with the select. I'm using Object for now.
3. Why the only way to populate the html:optionsCollection in the Action is passing the object in the request object as an atribute in the next way:
request.setAttribute("lista", objectThatContainsList);instead
((ActionForm)form).setListaPropiedades(objectThatContainsList);why's that? I have the same question when i'm populatina a normal html table using a logic:iterate tag or using a display:table tag from displaytag library.

Answer 1

Ok, you have one big misconception here - you're using the same name/property for both the select component and its contents.
The html:select should refer you to ONE selected value (in this case an int). It should tie to a field on your action form.
The html:optionsCollection should refer to a list of beans used to populate this select component.
<html:select property="selectedItem">
<html:optionsCollection name="myList" property="listOfProperties" value="varValor" label="varLabel" />
</html:select>
1. Why i have to establish the parameters property and name for bot html:select and html:optionsCollection? Why not only in html:select or only html:optionsCollection?Because they actually refer to two different things, and should be two different values.
html:options gets the list of possible values
html:select stores the "selected" option. (consider what you would have if you just used a standard html:input here, and typed the id directly in - THATS the property to bind to)
2. In the ActionForm for my JSP i don�t know what data type have to use to declare the variable that's linked with the option or with the select. I'm using Object for now.You do now - because it is declared/mapped seperately
3. Why the only way to populate the html:optionsCollection in the Action is passing the object in the request object as an atribute in the next way:Its not.
The way you mentioned is also valid. If both the "selectedItem" and "listOfItems" are properties on your action form, you can leave out the "name" attribute, and they will be found there.
However if you are dealing with request scoped beans, you will have to populate the list on each access of the page - you will need a "load" action to poupulate the bean with the items for the dropdown, and make sure that it is always populated when you return to it (eg on an error condition).
That is why setting it as an attribute is sometimes preferable.
Cheers,
evnafets