Accessing the original expression of the ValueExpression to the taglib component

Can I access the ValueExpression string passed as an attribute value to my taglib component?

My goal is to programmatically infer the missing attribute values ​​from it. In this case, I try to avoid repeating the attribute as a literal.

Now:

<a:columnText title="name" value="#{entity.name}" sortBy="entity.name" />

      

        
        
        
      

    

:

<a:columnText title="name" value="#{entity.name}" />

      

        
        
        
      

    

-taglib.xml

<tag>
    <tag-name>columnText</tag-name>
    <source>column-text.xhtml</source>
    <attribute>
        <name>value</name>
        <required>true</required>
    </attribute>
    <attribute>
        <name>title</name>
        <required>false</required>
    </attribute>
    <attribute>
        <name>sortBy</name>
        <required>false</required>
    </attribute>
</tag>

      

        
        
        
      

    

columnar text.xhtml

<ui:composition xmlns="http://www.w3.org/1999/xhtml" xmlns:ui="http://java.sun.com/jsf/facelets"
                xmlns:p="http://primefaces.org/ui" xmlns:h="http://java.sun.com/jsf/html"
                xmlns:a="http://www.kwa.nl/jsf/app-legacy" xmlns:c="http://java.sun.com/jstl/core">

    <c:if test="#{empty sortBy}">
        <a:expressionAsLiteral var="#{sortBy}" value="#{value}" />
    </c:if>

    <p:column headerText="#{title}" sortable="true" sortBy="#{sortBy}">
        <h:outputText value="#{value}"/>
        <a:sortByUnwrapper/>
    </p:column>
</ui:composition>

      

        
        
        
      

    

<a:expressionAsLiteral />

is intended to expand ValueExpression '# {value}' to '# {entity.name}' and set '# {sortBy}' to the literal 'entity.name'. This example feeds the sort column sortBy.

public class ExpressionAsLiteral extends TagHandler {

    private final TagAttribute var;
    private final TagAttribute value;

    public ExpressionAsLiteral(TagConfig config) {
        super(config);
        var = getRequiredAttribute("var");
        value = getRequiredAttribute("value");
    }    

    @Override
    public void apply(FaceletContext ctx, UIComponent parent) throws IOException {
       // abstracted for example.
       setAsLiteral(ctx, var, unwrapFaceletAttributeValue(ctx,value));
    }
}

      

        
        
        
      

    

My debugger tells me that the required information is hidden in the ValueExpressionImpl value private VariableMapper varMapper

. My problem is unpacking the returned ValueExpressionImpl without resorting to code smells.

My google-fu is failing. I feel like my approach is wrong, any advice?

EDIT # 1: Tried to do the following. Results in #{value}

instead of the desired attribute value #{iRow.title}

.

valueExpressionString = value.getValueExpression(ctx, Object.class).getExpressionString();