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Posted to users@myfaces.apache.org by "l.penet@senat.fr" <l....@senat.fr> on 2013/03/06 10:22:30 UTC
EL expressions as custom component attributes
I do not succeed in passing EL expressions as attributes of a custom
component used in a tag file.
I could not find a clear doc on how to do that with EL 2.2.
My use case is the following :
1. a tag file taking attribute "context" as a parameter
2. inside the tag file, using a home made custom component taking
"bean" as a parameter
Context is an instance of an in-house class hierarchy. Bean is most
often in this case #{context.selected}.
If I use my tag file the following way in a top level f:view :
|<my:tag context="#{adminContext}"/>|
And inside my:tag definition :
|<my:custom bean="#{context.selected}"/>|
In my custom component, I have tried accessors like
|public ValueExpression getBean() {
return (ValueExpression) getStateHelper().eval(PropertyKeys.bean);
}
public void setBean(ValueExpression param) {
getStateHelper().put(PropertyKeys.bean, param);
}|
and attribute declaration of custom component in taglib like :
|<attribute>
<description>Nom du bean à afficher</description>
<name>bean</name>
<required>true</required>
<deferred-value>
<type>java.lang.Object</type>
</deferred-value>
</attribute>|
and attribute declaration of the tag file like :
|<attribute>
<name>context</name>
<deferred-value>
<type>java.lang.Object</type>
</deferred-value>
<required>true</required>
</attribute>|
I always get a "cast to ValueExpression exception" when calling getBean().
In a method of the custom component called by encodeBegin, I noticed
that I can access the attribute using getValueExpression("bean").
It returns an instance of ContextAwareTagValueExpressionUEL. Its
_wrapped attribute points to an instance of WrappedValueExpression,
encapsulating a ValueExpressionImpl whose value (expr) is
#{context.selected}. This instance of ValueExpressionImpl also has a
VariableMapper handling the translation of "context" to "adminContext".
Its expected type is javax.el.ValueExpression. This must cause my
exception...
How can I make it works ?
Thanks in advance.
I am using MyFaces 2.1.9, CODI 1.0.5, OpenWebBeans 1.1.6, Tomcat 7.0.32.
(question also asked on
http://stackoverflow.com/questions/15229708/el-expressions-as-custom-component-attributes
|
| AVANT D'IMPRIMER, PENSEZ A L'ENVIRONNEMENT.
|
Re: EL expressions as custom component attributes
Posted by "l.penet@senat.fr" <l....@senat.fr>.
On 06/03/2013 20:02, Leonardo Uribe wrote:
> Hi
>
> There are good reasons to avoid use VariableMapper. This class is used
> when the EL expressions are built to store some values required to
> resolve the expression later, making the expression not cacheable,
> because the content of VariableMapper could change at any time and in
> that way, it is not possible to reuse the same expression.
>
> The wrappers used for EL expressions are there to ensure proper
> context initialization. For example, when the EL expression is
> evaluated, the reference for the composite component must be pushed on
> to the stack.
>
> This process is done by facelets, so create a value expression like
> #{cc} programatically will not have the same effect as if it is
> created by facelets compiler (if it is located inside composite
> component .xhtml file).
>
> If you need some kind of global context in your pages, the best way is
> write a custom EL resolver. Other option is write an specific facelets
> function, and pass the reference to the composite component to
> retrieve the specified context and finally resolve it properly. For
> example:
>
> #{utils:context(cc).selected.attribute1}
>
> Really I don't know what you are trying to do, but I hope these ideas
> could help.
Thank you for this reply.
My application manages collections of tens of types.
It is some kind of CRUD + collections management.
As I do not like to copy paste code over and over, I wrote a lib that
analyses those types
to decide how they should be displayed or edited. It uses custom
annotations and information
provided by hibernate (all those type are hibernate objects). I call
this information a "mapping".
For collections that should be displayed as a datatable, I use this
mapping to dynamically instantiate columns
So, I have code like :
<p:dataTable ... var="elutit">
<c:forEach items="#{mapper.mappings}" var="curProp">
<my:displayColumn mapper="#{mapper}" bean="elutit"
mappingDesc="#{curProp}"/>
</c:forEach>
</p:dataTable>
my:displayColumn is a custom class extending Column that will use the
mapping and the bean to correctly display a property as a column.
To ensure dynamic update, the values and parameters of the display
controls added as children of this custom column are set as
ValueExpression-s.
In this datatable example I have no problem, as the bean name (here
"elutit") is local to the control. Value expression will be for example
#{elutit.property1}
For generic editions, I have controls that derives from layouting
controls such as panels. As I like PrimeFaces, I most often use a
control derivating from PanelGrid. This control takes various parameters
as attributes : the mapper, the bean, etc. Similar to the dataTable, it
adds edition controls as children, setting their values with
ValueExpression-s.
The bean to display is specified as an attribute of this custom control,
with an EL expression : #{myBean}.
I need to get a hand on an EL expression that can reference myBean in
the ValueExpressions I generate for display controls.
I use this EL Expression as a parameter of my generated ValueExpressions
In some cases, a property value will not be just #{myBean.property1} but
#{my:customFunction(myBean)}, with #{my:customFunction(<inst>)}
specified in mapping configuration and <inst> replaced by the "right" EL
expression.
Following your advice, I took a look at custom EL resolvers. It is
definitely a good solution for mapping "absolute" names.
I did not see how it can help me in my case of a custom control used
inside a tag file.
In this case, you can have the top level variable A specified as
parameter B to the tag component, using it as parameter C of the custom
component.
I need a way to get track of these successive mappings. Ideally, I would
be able to instantiate my ValueExpressions with the exact same context,
and so the same variable mappings.
Thanks again for your attention, I hope my English makes sense...
Best regards,
Ludovic
|
| AVANT D'IMPRIMER, PENSEZ A L'ENVIRONNEMENT.
|
Re: EL expressions as custom component attributes
Posted by Leonardo Uribe <lu...@gmail.com>.
Hi
There are good reasons to avoid use VariableMapper. This class is used
when the EL expressions are built to store some values required to
resolve the expression later, making the expression not cacheable,
because the content of VariableMapper could change at any time and in
that way, it is not possible to reuse the same expression.
The wrappers used for EL expressions are there to ensure proper
context initialization. For example, when the EL expression is
evaluated, the reference for the composite component must be pushed on
to the stack.
This process is done by facelets, so create a value expression like
#{cc} programatically will not have the same effect as if it is
created by facelets compiler (if it is located inside composite
component .xhtml file).
If you need some kind of global context in your pages, the best way is
write a custom EL resolver. Other option is write an specific facelets
function, and pass the reference to the composite component to
retrieve the specified context and finally resolve it properly. For
example:
#{utils:context(cc).selected.attribute1}
Really I don't know what you are trying to do, but I hope these ideas
could help.
regards,
Leonardo Uribe
2013/3/6 l.penet@senat.fr <l....@senat.fr>:
> Well,
>
> reading my message again, I found that I still does not properly explain my
> problem.
>
> It is not really to pass a bean using an EL expression.
>
> To do that, you just declare getBean/setBean as returning/taking as
> parameter an Object, and that's done.
>
> My custom component generates itself some custom EL.
>
> So, I need to grab the ValueExpression used to pass this bean.
>
> I found that I can do so using getValueExpression("bean") in my custom
> component method.
> However, I found no clean way (I mean, other than reflection) to get a hand
> on the wrapper VariableMapper, to perform mappings before reusing the
> expression or to specify to use this mapper when evaluating my custom
> expressions.
>
> In my example, my custom component generated EL expressions such as
> #{context.selected.attribute1} . Without proper VariableMapper, evaluation
> just fails as "context" is not defined.
>
> Thanks in advance for your patience.
>
> Ludovic
>
> On 06/03/2013 10:22, l.penet@senat.fr wrote:
>>
>>
>> I do not succeed in passing EL expressions as attributes of a custom
>> component used in a tag file.
>>
>> I could not find a clear doc on how to do that with EL 2.2.
>>
>> My use case is the following :
>>
>> 1. a tag file taking attribute "context" as a parameter
>> 2. inside the tag file, using a home made custom component taking
>> "bean" as a parameter
>>
>> Context is an instance of an in-house class hierarchy. Bean is most often
>> in this case #{context.selected}.
>>
>> If I use my tag file the following way in a top level f:view :
>>
>> |<my:tag context="#{adminContext}"/>|
>>
>> And inside my:tag definition :
>>
>> |<my:custom bean="#{context.selected}"/>|
>>
>> In my custom component, I have tried accessors like
>>
>> |public ValueExpression getBean() {
>> return (ValueExpress
>> ion) getStateHelper().eval(PropertyKeys.bean);
>> }
>>
>> public void setBean<
>> span class="pun" style="margin: 0px; padding: 0px; border: 0px; font-size:
>> 14px; vertical-align: baseline; background-color: transparent; color: rgb(0,
>> 0, 0); background-position: initial initial; background-repeat: initial
>> initial;">(ValueExpression param) {
>> getStateHelper().put(P
>> ropertyKeys.bean, param<
>> span class="pun" style="margin: 0px; padding: 0px; border: 0px; font-size:
>> 14px; vertical-align: baseline; background-color: transparent; color: rgb(0,
>> 0, 0); background-position: initial initial; background-repeat: initial
>> initial;">);
>>
>> }|
>>
>> and attribute declaration of custom component in taglib like :
>>
>> |<attribute>
>> <description>Nom du bean à afficher</description>
>> <name>bean</name>
>> <required>true</required>
>> <deferred-value>
>> <type>java.lang.Object</type>
>> </deferred-value>
>> </attribute>|
>>
>> and attribute declaration of the tag file like :
>>
>> |<attribute>
>> <name>context</name>
>> <deferred-value>
>> <type>java.lang.Object</type>
>> </deferred-value>
>> <required>true</required>
>> </attribute>|
>>
>> I always get a "cast to ValueExpression exception" when calling getBean().
>>
>> In a method of the custom component called by encodeBegin, I noticed that
>> I can access the attribute using getValueExpression("bean").
>>
>> It returns an instance of ContextAwareTagValueExpressionUEL. Its _wrapped
>> attribute points to an instance of WrappedValueExpression, encapsulating a
>> ValueExpressionImpl whose value (expr) is #{context.selected}. This instance
>> of ValueExpressionImpl also has a VariableMapper handling the translation of
>> "context" to "adminContext". Its expected type is javax.el.ValueExpression.
>> This must cause my exception...
>>
>> How can I make it works ?
>>
>> Thanks in advance.
>>
>> I am using MyFaces 2.1.9, CODI 1.0.5, OpenWebBeans 1.1.6, Tomcat 7.0.32.
>>
>> (question also asked on
>> http://stackoverflow.com/questions/15229708/el-expressions-as-custom-component-attributes
>>
>
>
> |
> | AVANT D'IMPRIMER, PENSEZ A L'ENVIRONNEMENT.
> |
Re: EL expressions as custom component attributes
Posted by "l.penet@senat.fr" <l....@senat.fr>.
Well,
reading my message again, I found that I still does not properly explain
my problem.
It is not really to pass a bean using an EL expression.
To do that, you just declare getBean/setBean as returning/taking as
parameter an Object, and that's done.
My custom component generates itself some custom EL.
So, I need to grab the ValueExpression used to pass this bean.
I found that I can do so using getValueExpression("bean") in my custom
component method.
However, I found no clean way (I mean, other than reflection) to get a
hand on the wrapper VariableMapper, to perform mappings before reusing
the expression or to specify to use this mapper when evaluating my
custom expressions.
In my example, my custom component generated EL expressions such as
#{context.selected.attribute1} . Without proper VariableMapper,
evaluation just fails as "context" is not defined.
Thanks in advance for your patience.
Ludovic
On 06/03/2013 10:22, l.penet@senat.fr wrote:
>
> I do not succeed in passing EL expressions as attributes of a custom
> component used in a tag file.
>
> I could not find a clear doc on how to do that with EL 2.2.
>
> My use case is the following :
>
> 1. a tag file taking attribute "context" as a parameter
> 2. inside the tag file, using a home made custom component taking
> "bean" as a parameter
>
> Context is an instance of an in-house class hierarchy. Bean is most
> often in this case #{context.selected}.
>
> If I use my tag file the following way in a top level f:view :
>
> |<my:tag context="#{adminContext}"/>|
>
> And inside my:tag definition :
>
> |<my:custom bean="#{context.selected}"/>|
>
> In my custom component, I have tried accessors like
>
> |public ValueExpression getBean() {
> return (ValueExpress
> ion) getStateHelper().eval(PropertyKeys.bean);
> }
>
> public void setBean<
> span class="pun" style="margin: 0px; padding: 0px; border: 0px; font-size: 14px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 0); background-position: initial initial; background-repeat: initial initial;">(ValueExpression param) {
> getStateHelper().put(P
> ropertyKeys.bean, param<
> span class="pun" style="margin: 0px; padding: 0px; border: 0px; font-size: 14px; vertical-align: baseline; background-color: transparent; color: rgb(0, 0, 0); background-position: initial initial; background-repeat: initial initial;">);
> }|
>
> and attribute declaration of custom component in taglib like :
>
> |<attribute>
> <description>Nom du bean à afficher</description>
> <name>bean</name>
> <required>true</required>
> <deferred-value>
> <type>java.lang.Object</type>
> </deferred-value>
> </attribute>|
>
> and attribute declaration of the tag file like :
>
> |<attribute>
> <name>context</name>
> <deferred-value>
> <type>java.lang.Object</type>
> </deferred-value>
> <required>true</required>
> </attribute>|
>
> I always get a "cast to ValueExpression exception" when calling getBean().
>
> In a method of the custom component called by encodeBegin, I noticed
> that I can access the attribute using getValueExpression("bean").
>
> It returns an instance of ContextAwareTagValueExpressionUEL. Its
> _wrapped attribute points to an instance of WrappedValueExpression,
> encapsulating a ValueExpressionImpl whose value (expr) is
> #{context.selected}. This instance of ValueExpressionImpl also has a
> VariableMapper handling the translation of "context" to
> "adminContext". Its expected type is javax.el.ValueExpression. This
> must cause my exception...
>
> How can I make it works ?
>
> Thanks in advance.
>
> I am using MyFaces 2.1.9, CODI 1.0.5, OpenWebBeans 1.1.6, Tomcat 7.0.32.
>
> (question also asked on
> http://stackoverflow.com/questions/15229708/el-expressions-as-custom-component-attributes
>
>
|
| AVANT D'IMPRIMER, PENSEZ A L'ENVIRONNEMENT.
|