Access iteration variable in passthrough attribute? - jsf

Question

I'm wondering why I get a NullPointerException on the following:
<h:dataTable value="#{testBean.entities}" var="d">
<h:column p:data-order="#{d.modifiedOn}">
<f:facet name="header">Date</f:facet>
<h:outputText value="#{d.modifiedOn}">
<f:convertDateTime pattern="#{msg.datePattern}" />
</h:outputText>
</h:column>
</h:dataTable>
Where the p namespace is xmlns:p="http://xmlns.jcp.org/jsf/passthrough", modifiedOn is a (non-null) Date field.
The exception looks like this:
Caused by: java.lang.NullPointerException
at com.sun.faces.renderkit.html_basic.HtmlResponseWriter.getAttributeValue(HtmlResponseWriter.java:1211)
at com.sun.faces.renderkit.html_basic.HtmlResponseWriter.flushAttributes(HtmlResponseWriter.java:1171)
at com.sun.faces.renderkit.html_basic.HtmlResponseWriter.closeStartIfNecessary(HtmlResponseWriter.java:1113)
at com.sun.faces.renderkit.html_basic.HtmlResponseWriter.writeText(HtmlResponseWriter.java:936)
at com.sun.faces.facelets.el.ELText$ELTextVariable.writeText(ELText.java:240)
at com.sun.faces.facelets.compiler.TextInstruction.write(TextInstruction.java:85)
at com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(UIInstructions.java:82)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:302)
at com.sun.faces.renderkit.html_basic.TableRenderer.renderHeader(TableRenderer.java:339)
However, use of #{d.modifiedOn} is fine in any non-passthrough attributes like headerClass. As is any value not referencing the iteration variable in a passthrough attribute.
My question is: is this intended?
This is using Wildfly-8.0.0.Final's JSF implementation, version 2.2.5-jbossorg-3.
In case anyone's wondering: I'm trying to support datatables orthogonal data attributes to enhance my tables.
Edited to add: I've also tried, but got the same Exception, with adding the following to the <h:column>:
<f:passThroughAttribute name="data-order" value="#{d.modifiedOn}" />
This is apparently caused by JSF trying to render this attribute on the header where rowIndex is -1 and iteration data is not yet present. So there's an hack solution to my specific problem:
<h:column p:data-order="#{empty d or empty d.modifiedOn ? '' : d.modifiedOn.time}">
...
</h:column>
Which still renders an empty/useless data-order attribute into my thead.
Further testing:
More testing has confirmed my suspicion that this only occurs with a <f:facet name="header"> on any column (doesn't have to be the one with the attribute). Leaving those out defeats my goal of using the table as a base for datatables since that requires a well-formed table with a <thead>.

Answer 1

Is this intended? Definitelly it's not. Furthermore, here is the definition of a passthrough attribute according to the JSF 2.2 specification:
Pass Through Attributes
For any given JSF component tag in a view, the set of available attributes that component supports is determined by a
combination of the UIComponentand Renderer for that tag. In some cases the value of the attribute is interpreted by
the UIComponentor Renderer(for example, the columns attribute of h:panelGrid) and in others the value is
passed straight through to the user agent (for example, the lang attribute of h:inputText).
In both cases, the
UIComponent/Renderer has a priori knowledge of the set of allowable attributes. Pass Through Attributes allows
the view author to list arbitrary name value pairs that are passed straight through to the user agent without interpretation
by the UIComponent/Renderer. This behavior is normatively specified in the “Rendering Pass Through Attributes”
section of the overview of the standard HTML_BASIC render kit.
So the only functionality of that kind of attributes is to notify the renderer that it must process the value for the attribute, but that it's not tied to any of the UIComponent features, so must end up at the final output.
I have performed a test with Tomcat 7 + Mojarra 2.2.6 and it perfectly works for me. HTML elements get rendered in the DOM tree with their data-order attribute, with the given date. That's the test case I've used:
<html xmlns:f="http://xmlns.jcp.org/jsf/core"
xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://xmlns.jcp.org/jsf/html"
xmlns:p="http://xmlns.jcp.org/jsf/passthrough">
<h:head />
<h:body>
<h:dataTable value="#{bean.entities}" var="entity">
<h:column p:data-order="#{entity.modifiedOn}">
#{entity.name}
</h:column>
</h:dataTable>
<h:messages />
</h:body>
</html>
#ManagedBean
#ViewScoped
public class Bean {
public class Entity {
private String name;
private Date modifiedOn;
public Entity(String name, Date modifiedOn) {
this.name = name;
this.modifiedOn = modifiedOn;
}
public Date getModifiedOn() {
return modifiedOn;
}
public String getName() {
return name;
}
}
/**
* Create a List of entities with dates differing from now to now + 2 days
*/
public List<Entity> entities = Arrays.asList(
new Entity("name1", new Date()), new Entity("name2", new Date(
new Date().getTime() + (1000 * 60 * 60 * 24))), new Entity(
"name0", new Date(new Date().getTime()
+ (1000 * 60 * 60 * 48))));
public List<Entity> getEntities() {
return entities;
}
}
This means it's a bug in your JSF implementation (implementation which I didn't know about BTW). Your best is opening a bug track unless the authors have already fixed it in a later version.
Edit
The rendering fails with the given error when there's an f:facet for header or footer involved for the datatable. Apparently, Mojarra tries to evaluate the passthrough value for the facet before building the iterator, that causes it to fail as the variable is not yet available. Opened an issue.
See also:
JSF 2.2 specification