从jsp调用动作方法

Question

Simply..I need to know whether these list attributes are doing same job or not.

<s:select name="city" label="City" list="cities" listKey="id" listValue="name" />

and

<s:select name="city" label="City" list="%{getCities()}" listKey="id" listValue="name" />

can we invoke action methods like above,If 'yes' what is the correct way to do that?

thanks,

Answer 1

list="cities" and list="%{getCities()}" both are exactly same. Both calls getter of List<City> cities in action class to read value from valuestack .

Both will throw an error if getter would be removed.

1. <s:select name="city" label="City" list="cities[0]" listKey="id" listValue="name" />

is evaluated to

a. <s:select name="city" label="City" list="%{cities[0]}" listKey="id" listValue="name" />

b. <s:select name="city" label="City" list="%{getCities().get(0)}" listKey="id" listValue="name" />

1, a & b are same because % forces OGNL evaluation. that will query stack for particular property.

OGNL supports collections, that's why we can use this three.

We call actions when we use particular need.

For Example

 <s:url id="databaseList" action="fetch-citynames" />
 <sd:autocompleter key="search"
     href="%{databaseList}" name="searchText" />

Here fetch-citynames return json list.

Also see this link

Actually I read from here

The principal reason is because %{} syntax is used to force OGNL evaluation where Struts would otherwise be treating the value as a String literal.

For example,

  <s:property value="name" />

will look for a name property in the value stack ie is a value retrieved by calling getName().

If you wanted to force it to use literal value "name", you will need to use the %{} syntax -

 <s:property value="%{'name'}" />

But in the case of <s:select list="" /> it uses OGNL Collection Construction

Here is how OGNL call methods.. See here