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

What this means is that OGNL allows many objects in the context, but unless the object you are trying to access is the root, it must be prepended with a namespaces such as @bar. Now let's talk about how XWork is a little different...

...

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. WebWork Struts 2 will cut the stack and still returned return back a CompoundRoot object. To get the top of that particular stack cut, use [0].top

Accessing static properties

OGNL supports accessing static properties as well as static methods. As the OGNL docs point out, you can explicetly call statics by doing the following

By default, Struts 2 is configured to disallow this--to enable OGNL's static member support you must set the struts.ognl.allowStaticMethodAccess constant to true via any of the Constant Configuration methods.

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

...

Besides 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.

Old Expression	New Expression
foo/blah	foo.blah
foo/someMethod()	foo.someMethod()
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="490d3f5d-52dd-4cd4-bc6f-d6c805132293"><ac:plain-text-body><![CDATA[	../bar/blah	[1].bar.blah	]]></ac:plain-text-body></ac:structured-macro>
@baz	not directly supported, but #baz is similar<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="d15e7642-d16d-4185-82ae-4e1fc54ad71c"><ac:plain-text-body><![CDATA[
.	'top' or [0]	]]></ac:plain-text-body></ac:structured-macro>

WebWork-specific named objects

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.