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From "Leonardo Uribe (JIRA)" <>
Subject [jira] Created: (MYFACES-3027) cc:attribute type="java.lang.Integer" does not enforce Integer when value is taken from facelets template
Date Fri, 04 Feb 2011 21:03:30 GMT
cc:attribute type="java.lang.Integer" does not enforce Integer when value is taken from facelets

                 Key: MYFACES-3027
             Project: MyFaces Core
          Issue Type: Bug
            Reporter: Leonardo Uribe


[jsr-314-open] Composite component metadata runtime behavior

I checked in deep how attribute for composite components works, and here is what I found.

This is the javadoc of cc:attribute type:

"... Declares that this attribute must be a ValueExpression whose expected type is given by
the value of this attribute. If not specified, and no "method-signature" attribute is present,
java.lang.Object  is assumed. This attribute is mutually exclusive with the "method-signature"
attribute. If both attributes are present, the "method-signature" attribute is ignored. ..."

MyFaces (2.0.3 and earlier) implemented what javadoc says, but in practice Mojarra (tested
2.0.3 and 2.1.0 snapshot branch) behaves different in this case. For example, if it is written

 <cc:attribute name="foo" type="java.lang.Integer"/>

With the following component definition:

 <comp:bar foo="5"/>

In MyFaces the String "5" is stored on the map, but in Mojarra an Integer 5 is. It is obvious
the right behavior is the one shown by Mojarra, even if the javadoc is to explicit about this

Now think about a little bit more complex example:

 <cc:attribute name="foo" type="java.lang.Integer" default="5"/>

both MyFaces and Mojarra fails in this case, because the default is assumed to be a String
"5" and not an Integer 5.

It is obvious the author expect "type" attribute enforce the value to the type using EL coercions,
like it is done for all other components, right? Maybe the javadoc is not explicit, but it
is clear the way to go.

Now try to get a value programatically instead use EL expressions.


the default is just ignored. Why? by the spec, composite component default values are handled
by "Composite Component Attribute EL Resolver". This is what JSF 2.0 spec section
says about it (getValue description)

"... get(): if the result of calling get() on the component attributes map is null, and a
default value was declared in the composite component metadata, the value will be a ValueExpression.
Evaluate it and return it. Otherwise, simply return the value from the component attributes
map. ..."

In my opinion, we should do that on UIComponent.getAttributes() map instead on an EL resolver,
after all we could use the value stored on BEANINFO_KEY to get the descriptor and handle the
default value only if all fails.

But here is the big question: It is really necessary to support that case? The common case
is lookup attributes map using an EL expression #{cc.attrs.myproperty}. This could be necessary
only if we do a composite component with a custom component type and we need to play with
properties defined on the component class and the composite component definition, but that's
very exotic (but theorically possible).

Now it is possible to answer the questions (in my personal opinion, based on the previous

1.  Should JSF implementations be making use of composite component metadata (like "type")
at runtime to enforce the intentions of the composite component author?

Ans: Really this is already done, because ValueExpressions are created and values are coerced
taking into account the type, but we don't have any code on the default component attribute
map class that enforces it.

2.  Should this behavior be specified?

Ans: the javadoc of cc:attribute type is incomplete and definitively needs to be fixed.

3.  Are there other places where we have similar metadata (eg. Facelets taglib.xml files)
that we should review as well?

Ans: User tag handlers does not have any semantic about how to handle attributes, so there
is nothing we can do or other places to review (after all, one of the intentions of composite
components is provide a transparent way to create components with the flexibility of custom
facelets tag handlers).

What do we need to do? Fix the bugs on MyFaces and Mojarra related to this issue.

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