Re: Casting beans in JSP

[Craig R. McClanahan]

On Fri, 20 Apr 2001, John Raley wrote:

 Try using bean:define and specifying the type you want.  The 'id'
 attribute value in bean:define will be the downcast reference.
 
 Example:
 % ... a bean of type Foo is in the page under the attribute name 'aFoo'
 %
 bean:define name='aFoo' type='mypkg.SubFoo' id='aSubFoo'/
 
 aSubFoo now refers to aFoo through a reference of type SubFoo.
 

This works as advertised, but I should point out that if you are only
using Struts tags (or jsp:getProperty to access the properties of the
actual bean, casting is not strictly necessary.

Craig

Casting beans in JSP

[Chris Butler]

heya folx,

is there anyway to use a tag to cast an object from
one type to another?  just curious.  the reason is
that a top level bean implements a generic interface
and i need to access the 'actual' object rather than a
the generic attributes returned by interface.

i'm loathe to use any java in my JSPs, so i'm looking
for some other sort of solution.

i'm going to look for a solution on the server side,
but i think it's a fairly normal design pattern.

thoughts?  ideas?

chris

Re: Casting beans in JSP

[Peter Alfors]

I don't know if one already exists, but if not...

You could write your own that would take
pageContext attribute id (scripting variable name) of the object to
cast
the type to cast it to.  (fully qualified of coarse)
pageContext attribute id (scripting variable name) of the new object

Something like:
CAST id="myGenericObject" type="myComp.ActualClass"
castid="myActualClass"/

There would be very little code involved.

Take a look at the DefineTag in Struts.  It has an example of making an
object available as a scripting variable.

HTH,
Pete


Chris Butler wrote:

 heya folx,

 is there anyway to use a tag to cast an object from
 one type to another?  just curious.  the reason is
 that a top level bean implements a generic interface
 and i need to access the 'actual' object rather than a
 the generic attributes returned by interface.

 i'm loathe to use any java in my JSPs, so i'm looking
 for some other sort of solution.

 i'm going to look for a solution on the server side,
 but i think it's a fairly normal design pattern.

 thoughts?  ideas?

 chris


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Re: Casting beans in JSP

[John Raley]

Try using bean:define and specifying the type you want.  The 'id'
attribute value in bean:define will be the downcast reference.

Example:
% ... a bean of type Foo is in the page under the attribute name 'aFoo'
%
bean:define name='aFoo' type='mypkg.SubFoo' id='aSubFoo'/

aSubFoo now refers to aFoo through a reference of type SubFoo.


Chris Butler wrote:

 heya folx,

 is there anyway to use a tag to cast an object from
 one type to another?  just curious.  the reason is
 that a top level bean implements a generic interface
 and i need to access the 'actual' object rather than a
 the generic attributes returned by interface.

 i'm loathe to use any java in my JSPs, so i'm looking
 for some other sort of solution.

 i'm going to look for a solution on the server side,
 but i think it's a fairly normal design pattern.

 thoughts?  ideas?

 chris