ValueExpression: how to get base Object? - jsf-2

Question

#FacesValidator("uniqueValidator")
public class UniqueValidator implements Validator
{
#Override
public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException
{
if(context == null)
{
throw new NullPointerException();
}
if(component == null)
{
throw new NullPointerException();
}
ValueExpression valueExpression = component.getValueExpression("value");
if(valueExpression == null)
{
return;
}
ValueReference valueReference = valueExpression.getValueReference(context.getELContext());
if(valueReference == null)
{
return;
}
Object base = valueReference.getBase();
Object property = valueReference.getProperty();
Tracer.out(base, property);
.....
}
}
and ValueReference is always null.
what's wrong?

Answer 1

thank you BeanValidator :)
public class ValueExpressionAnalyzer
{
public static ValueReference getReference(ELContext elContext, ValueExpression expression)
{
InterceptingResolver resolver = new InterceptingResolver(elContext.getELResolver());
try
{
expression.setValue(new InterceptingContext(elContext, resolver), null);
}
catch(ELException ele)
{
return null;
}
ValueReference reference = resolver.getValueReference();
if(reference != null)
{
Object base = reference.getBase();
if(base instanceof CompositeComponentExpressionHolder)
{
ValueExpression ve = ((CompositeComponentExpressionHolder) base).getExpression((String) reference.getProperty());
if(ve != null)
{
reference = getReference(elContext, ve);
}
}
}
return reference;
}
private static class InterceptingContext extends ELContext
{
private final ELContext context;
private final ELResolver resolver;
public InterceptingContext(ELContext context, ELResolver resolver)
{
this.context = context;
this.resolver = resolver;
}
// punch in our new ELResolver
#Override
public ELResolver getELResolver()
{
return resolver;
}
// The rest of the methods simply delegate to the existing context
#Override
public Object getContext(Class key)
{
return context.getContext(key);
}
#Override
public Locale getLocale()
{
return context.getLocale();
}
#Override
public boolean isPropertyResolved()
{
return context.isPropertyResolved();
}
#Override
public void putContext(Class key, Object contextObject)
{
context.putContext(key, contextObject);
}
#Override
public void setLocale(Locale locale)
{
context.setLocale(locale);
}
#Override
public void setPropertyResolved(boolean resolved)
{
context.setPropertyResolved(resolved);
}
#Override
public FunctionMapper getFunctionMapper()
{
return context.getFunctionMapper();
}
#Override
public VariableMapper getVariableMapper()
{
return context.getVariableMapper();
}
}
private static class InterceptingResolver extends ELResolver
{
private final ELResolver delegate;
private ValueReference valueReference;
public InterceptingResolver(ELResolver delegate)
{
this.delegate = delegate;
}
public ValueReference getValueReference()
{
return valueReference;
}
// Capture the base and property rather than write the value
#Override
public void setValue(ELContext context, Object base, Object property, Object value)
{
if(base != null && property != null)
{
context.setPropertyResolved(true);
valueReference = new ValueReference(base, property.toString());
}
}
// The rest of the methods simply delegate to the existing context
#Override
public Object getValue(ELContext context, Object base, Object property)
{
return delegate.getValue(context, base, property);
}
#Override
public Class<?> getType(ELContext context, Object base, Object property)
{
return delegate.getType(context, base, property);
}
#Override
public boolean isReadOnly(ELContext context, Object base, Object property)
{
return delegate.isReadOnly(context, base, property);
}
#Override
public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base)
{
return delegate.getFeatureDescriptors(context, base);
}
#Override
public Class<?> getCommonPropertyType(ELContext context, Object base)
{
return delegate.getCommonPropertyType(context, base);
}
}
}

Answer 2

Have a look at Omnifaces ExpressionInspector. Seems in JSF 2.x its not implemented and always returns null.
https://showcase.omnifaces.org/el/ExpressionInspector