tag attributes as bean properties

[Borislav Iordanov <bo...@kobrix.com>]

Hi guys,

This is more a question for tomcat developers I guess. I'm working with
Tomcat 4.1.18. 

The JSP 1.2 specification states that a container should interpret tag
attributes as bean properties following the Java Beans specification.
Does Tomcat then rely on a BeanInfo associated with a bean to find out
about property setters and getters? It doesn't seem so since I defined a
BeanInfo class for a tag handler class and the
'BeanInfo.getPropertyDescriptors' never gets called.

My goal is the following: I would like to allow a tag attribute which is
semantically a boolean to be set either through 

(1) a string ("true" or "false") or 
(2) a run-time expression (e.g. '<%= bar.getFoo() != null %>') or 
(3) an EL expression (e.g. "${not empty bla.foo}") 

The problem is that the EL expression gets converted at translation time
to a false boolean. Therefore, I would like to bypass the standard
String->primitive_type conversions performed by the JSP translator.  

Thanks a lot in advance,
Boris
____________________________________________
Borislav Iordanov
Chief Architect
TICL - a RAD toolkit for server-side Java
http://www.kobrix.com


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Re: tag attributes as bean properties

["David M. Karr" <dm...@earthlink.net>]

>>>>> "Borislav" == Borislav Iordanov <bo...@kobrix.com> writes:

    Borislav> Hi guys,
    Borislav> This is more a question for tomcat developers I guess. I'm working with
    Borislav> Tomcat 4.1.18. 

    Borislav> The JSP 1.2 specification states that a container should interpret tag
    Borislav> attributes as bean properties following the Java Beans specification.
    Borislav> Does Tomcat then rely on a BeanInfo associated with a bean to find out
    Borislav> about property setters and getters? It doesn't seem so since I defined a
    Borislav> BeanInfo class for a tag handler class and the
    Borislav> 'BeanInfo.getPropertyDescriptors' never gets called.

    Borislav> My goal is the following: I would like to allow a tag attribute which is
    Borislav> semantically a boolean to be set either through 

    Borislav> (1) a string ("true" or "false") or 
    Borislav> (2) a run-time expression (e.g. '<%= bar.getFoo() != null %>') or 
    Borislav> (3) an EL expression (e.g. "${not empty bla.foo}") 

    Borislav> The problem is that the EL expression gets converted at translation time
    Borislav> to a false boolean. Therefore, I would like to bypass the standard
    String-> primitive_type conversions performed by the JSP translator.  

I don't read this list very often, so I don't know if you still need this
information.

I've had this exact problem.  I had a base class tag with attributes of certain
types (not string), and I defined a subclass tag whose attribute values are
evaluated with the EL.

For instance, assume your attribute is named "foo", as defined in your TLD.  In
the base class, this is a boolean instance variable.

Along with my subclass, I have a BeanInfo class which maps the "foo" attribute
to a setter "setFooExpr()".  I have an instance variable named "fooExpr" in my
subclass, along with getter/setter "getFooExpr()" and "setFooExpr()".

In my "doStartTag()" method, I pass the value of "getFooExpr()" into the EL
evaluator and send the result to "setFoo()".

This will definitely deal with your cases "(1)" and "(3)", and I believe it
will handle "(2)", but I haven't tried that (I avoid scriptlets).

If you want to see numerous examples of this, I implemented this in the
Struts-EL contributed package in the Struts distribution.

-- 
===================================================================
David M. Karr          ; Java/J2EE/XML/Unix/C++
dmkarr@earthlink.net   ; SCJP; SCWCD




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