THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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XWork-specific
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language
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features
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The
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biggest
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addition
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that
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XWork
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provides
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on
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top
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of
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OGNL
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is
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the
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support
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for
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the
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ValueStack.
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While
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OGNL
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operates
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under
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the
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assumption
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there
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is
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only
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one
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"root",
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XWork's
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ValueStack
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concept
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requires
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there
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be
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many
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"roots".
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For
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example,
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suppose
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we
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are
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using
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standard
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OGNL
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(not
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using
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XWork)
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and
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there
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are
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two
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objects
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in
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the
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OgnlContext
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map:
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"foo"
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->
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foo
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and
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"bar"
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->
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bar
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and
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that
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the
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foo
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object
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is
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also
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configured
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to
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be
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the
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single
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root
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object.
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The
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following
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code
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illustrates
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how
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OGNL
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deals
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with
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these
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three
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situations:
| Code Block |
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{code:none} #foo.blah // returns foo.getBlah() #bar.blah // returns bar.getBlah() blah // returns foo.getBlah() because foo is the root {code} |
What
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this
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means
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is
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that
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OGNL
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allows
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many
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objects
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in
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the
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context,
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but
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unless
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the
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object
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you
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are
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trying
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to
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access
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is
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the
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root,
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it
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must
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be
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prepended
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with
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a
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namespaces
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such
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as
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@bar.
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Now
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let's
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talk
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about
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how
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XWork
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is
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a
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little
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different...
| Info | ||
|---|---|---|
| ||
In InXWork, the entire ValueStack is the root object in the context. But ratherRather than having your expressions get the object you want from the stack and then get properties from that (ie: peek().blah), XWork has a special OGNL PropertyAccessor that will automatically look at the all entries in the stack (from the top down) until it finds an object with the property you are looking for. |
For
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example,
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suppose
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the
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stack
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contains
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two
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objects:
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Animal
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and
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Person.
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Both
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objects
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have
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a
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"name"
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property,
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Animal
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has
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a
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"species"
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property,
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and
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Person
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has
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a
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"salary"
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property.
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Animal
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is
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on
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the
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top
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of
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the
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stack,
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and
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Person
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is
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below
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it.
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The
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follow
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code
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fragments
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help
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you
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get
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an
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idea
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of
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what
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is
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going
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on
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here:
| Code Block |
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{code:none} species // call to animal.getSpecies() salary // call to person.getSalary() name // call to animal.getName() because animal is on the top {code} |
In
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the
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last
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example,
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there
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was
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a
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tie
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and
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so
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the
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animal's
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name
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was
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returned.
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Usually
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this
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is
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the
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desired
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effect,
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but
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sometimes
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you
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want
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the
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property
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of
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a
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lower-level
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object.
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To
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do
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this,
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XWork
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has
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added
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support
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for
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indexes
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on
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the
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ValueStack.
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All
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you
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have
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to
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do
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is:
| Code Block |
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{code:none} \[0\].name // call to animal.getName() \[1\].name // call to person.getName() {code} h2. 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: {code:none} |
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
ognl expression | description |
|---|---|
[0].top | would get the top of the stack cut starting from element 0 in the stack (similar to top in this case) |
[1].top | would get the top of the stack cut starting from element 1 in the stack |
Accessing static properties
OGNL supports accessing static properties as well as static methods.
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:
| Code Block | ||
|---|---|---|
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@some.package.ClassName@FOO_PROPERTY
@some.package.ClassName@someMethod()
{code}
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However,
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XWork
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allows
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you
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to
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avoid
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having
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to
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specify
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the
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full
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package
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name
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and
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call
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static
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properties
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and
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methods
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of
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your
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action
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classes
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using
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the
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"vs"
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prefix:
| Code Block |
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<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()
|
"vs" stands for "value stack". The important thing to note here is that if the class name you specify is just "vs", the class for the object on the top of the stack is used. If you specify a number after the "vs" string, an object's class deeper in the stack is used instead.
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() |
../bar/blah | [1].bar.blah |
@baz | not directly supported, but #baz is similar |
. | 'top' or [0] |
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.
name | value |
|---|---|
| #action['foo'] or #action.foo | current action getter (getFoo()) |
#parameters['foo'] or #parameters.foo | request parameter ['foo'] (request.getParameter()) |
#request['foo'] or #request.foo | request attribute ['foo'] (request.getAttribute()) |
#session['foo'] or #session.foo | session attribute 'foo' |
#application['foo'] or #application.foo | ServletContext attributes 'foo' |
#attr['foo'] or #attr.foo | Access to PageContext if available, otherwise searches request/session/application respectively |