Page History

...

For example, suppose we are using standard OGNL (not using XWork) and there are two objects in the OgnlContext map: "foo" -> foo and "bar" -> bar and that the foo object is also configured to be the single root object. The following code illustrates how OGNL deals with these three situations:

#foo.blah // returns foo.getBlah()
#bar.blah // returns bar.getBlah()
blah      // returns foo.getBlah() because foo is the root

...

For example, suppose the stack contains two objects: Animal and Person. Both objects have a "name" property, Animal has a "species" property, and Person has a "salary" property. Animal is on the top of the stack, and Person is below it. The follow code fragments help you get an idea of what is going on here:

species    // call to animal.getSpecies()
salary     // call to person.getSalary()
name       // call to animal.getName() because animal is on the top

In the last example, there was a tie and so the animal's name was returned. Usually this is the desired effect, but sometimes you want the property of a lower-level object. To do this, XWork has added support for indexes on the ValueStack. All you have to do is:

[0].name   // call to animal.getName()
[1].name   // call to person.getName()

...

With expression like \ [0\] ... \ [3\] etc. Struts 2 will cut the stack and still return back a CompoundRoot object. To get the top of that particular stack cut, use [0].top

Accessing static properties

...

OGNL's static access looks like this:

@some.package.ClassName@FOO_PROPERTY
@some.package.ClassName@someMethod()

However, XWork allows you to avoid having to specify the full package name and call static properties and methods of your action classes using the "vs" prefix:

<at:var at:name="vs" />FOO_PROPERTY
<at:var at:name="vs" />someMethod()

<at:var at:name="vs1" />FOO_PROPERTY
<at:var at:name="vs1" />someMethod()

<at:var at:name="vs2" />BAR_PROPERTY
<at:var at:name="vs2" />someOtherMethod()

...

Differences from the WebWork 1.x EL

Wiki MarkupBesides the examples and descriptions given above, there are a few major changes in the EL since WebWork 1.x. The biggest one is that properties are no longer accessed with a forward slash \ (/\) but with a dot (.). Also, rather than using ".." to traverse down the stack, we now use "\[n\]" where n is some positive number. Lastly, in WebWork 1.x one could access special named objects (the request scope attributes to be exact) by using "@foo", but now special variables are accessed using "#foo". However, it is important to note that "#foo" does NOT access the request attributes. Because XWork is not built only for the web, there is no concept of "request attributes", and thus "#foo" is merely a request to another object in the OgnlContext other than the root.

Struts 2 Named Objects

Struts 2 places request parameters and request, session, and application attributes on the OGNL stack. They may be accessed as shown below.