<jsp:attribute> standard actions and Lists

[Ulrich Vormbrock]

Hi,

I've written a simple tag handler in order to print out several user data (from a form).
All works fine - except the last attribute named "programLanguages" - it deals with a List rather than with a String.
Below please find the tag "advice" which I've place into the "result.jsp":

<mine:advice>
    <jsp:attribute name="surname">${requestScope.user.surname}</jsp:attribute>
    <jsp:attribute name="forename">${requestScope.user.forename}</jsp:attribute>
    <jsp:attribute name="gender">${requestScope.user.gender}</jsp:attribute>
    <jsp:attribute name="programLanguages">${requestScope.user.programLanguages}</jsp:attribute>    		
</mine:advice>

When I run the result.jsp, I get the following exception:

org.apache.jasper.JasperException: Unable to convert string "[cpp, java, vb]" to class "java.util.List" for attribute "programLanguages": Property Editor not registered with the PropertyEditorManager

Instead, when I place the "programLanguages" attribute within my custom tag, it works fine:

<mine:advice programLanguages="${requestScope.user.programLanguages}">
    <jsp:attribute name="surname">${requestScope.user.surname}</jsp:attribute>
    <jsp:attribute name="forename">${requestScope.user.forename}</jsp:attribute>
    <jsp:attribute name="gender">${requestScope.user.gender}</jsp:attribute>  		
</mine:advice>

Any ideas?

[Frits Walraven]

Hi Ulrich,

The body of the <jsp:attribute> is always evaluated and converted into a String, and this is not possible for a List.
You can pass the List as an attribute of the customtag, like you already did.

Regards,
Frits

[Ulrich Vormbrock]

Hartelijk bedankt - many thanks, Frits!

Can you please tell me where I can find this kind of info?
I ask because I didn't find no hint concerning <jsp:attribute> in the "Head First" book ...

[Frits Walraven]

Graag gedaan - you are welcome!

JSP.5.10
For standard or custom action attributes that accept a request-time expression
value, the Container must evaluate the body of the <jsp:attribute> action and
use the result of this evaluation as the value of the attribute. The body of the
attribute action can be any JSP content in this case. If the type of the attribute
is not String, the standard type conversion rules are applied, as per
Section JSP.1.14.2.1, "Conversions from String values".

Regards,
Frits

[Ulrich Vormbrock]

Thank you again, Frits!
In future, I'll rely not only on the book, but also on the spec ...

[Frits Walraven]

In future, I'll rely not only on the book, but also on the spec ...

It can certainly help you on the newer topics like the <jsp:attribute>, <jsp:body> and so on

Also have a look at the following example where you can force the input of a custom tag attribute to be of a certain type
enum attribute

Regards,
Frits