nesting JSF expression strings

Question

I want to achieve this using dynamic parameters for value expressions:

<h:dataTable value="#{someBean.someValue}" var="field">
    <h:column>#{anotherBean[field]}</h:column>
</h:dataTable>

where field is 'user.name' or 'location.address.zip' or...

Is it possible?

Note that this is a simple example, I'm interested in ValueExpression not in dataTable component.

UPDATE now the question is: how to replace standard BeanELResolver?

looking in ELUtils:

    ...
    composite.addRootELResolver(IMPLICIT_RESOLVER);
    composite.add(FLASH_RESOLVER);
    composite.addPropertyELResolver(COMPOSITE_COMPONENT_ATTRIBUTES_EL_RESOLVER);
    addELResolvers(composite, associate.getELResolversFromFacesConfig());
    addVariableResolvers(composite, FacesCompositeELResolver.ELResolverChainType.Faces,
            associate);
    addPropertyResolvers(composite, associate);
    composite.add(associate.getApplicationELResolvers());
    composite.addRootELResolver(MANAGED_BEAN_RESOLVER);
    composite.addPropertyELResolver(RESOURCE_RESOLVER);
    composite.addPropertyELResolver(BUNDLE_RESOLVER);
    ...

but i don't fully understand resolver chain yet... so i'll go studying :)

UPDATE 2

this code works ;)

public class ExtendedBeanELResolver extends BeanELResolver
{
    @Override
    public Object getValue(ELContext context, Object base, Object property) throws NullPointerException, PropertyNotFoundException, ELException
    {
        try
        {
            return super.getValue(context, base, property);
        }
        catch(PropertyNotFoundException e)
        {
            try
            {
                Object value = base;

                for(String part : property.toString().split("\\."))
                {
                    value = super.getValue(context, value, part);
                }

                return value;
            }
            catch(PropertyNotFoundException e1)
            {
                context.setPropertyResolved(false);
            }
        }

        return null;
    }
}

Ellsworthellwood

no, i'm saying right: public List<String> getSomeValue() { ... } – Ellsworthellwood

Answer 1

This is by default not supported. You need a custom ELResolver here. Easiest is to extend the existing BeanELResolver.

Here's a kickoff example:

public class ExtendedBeanELResolver extends BeanELResolver {

    @Override
    public Object getValue(ELContext context, Object base, Object property)
        throws NullPointerException, PropertyNotFoundException, ELException
    {
        if (property == null || base == null || base instanceof ResourceBundle || base instanceof Map || base instanceof Collection) {
            return null;
        }

        String propertyString = property.toString();

        if (propertyString.contains(".")) {
            Object value = base;

            for (String propertyPart : propertyString.split("\\.")) {
                value = super.getValue(context, value, propertyPart);
            }

            return value;
        }
        else {
            return super.getValue(context, base, property);
        }
    }

}

To get it to run, register it as follows in faces-config.xml:

<application>
    <el-resolver>com.example.ExtendedBeanELResolver</el-resolver>
</application>

Carafe

this is exactly what i was looking for to solve this and some other little thing. thanks @BalusC, you save me so much time that you deserve part of my salary ;) – Ellsworthellwood

however declaring it in faces-config.xml overrides default CompositeELResolver. how to replace standard BeanELResolver in CompositeELResolver.elResolvers? – Ellsworthellwood

oops, i was wrong. it does not override, but get inserted before. see question update. – Ellsworthellwood

What problem exactly did it cause for you? The change should be transparent as it consistently delegates to the super. – Carafe

causes PropertyNotFoundException trying to read bundles properties. however doc states Because this resolver handles base objects of any type, it should be placed near the end of a composite resolver. Otherwise, it will claim to have resolved a property before any resolvers that come after it get a chance to test if they can do so as well. so i solved this catching PropertyNotFoundException and setting context.setPropertyResolved(false); – Ellsworthellwood

Right. Add a line if (base instanceof ResourceBundle) return null; to top. You might want to do the same for Map and Collection. I edited the example. – Carafe

@Carafe I saw that we can add multiple <el-resolver> in one single faces-config.xml (two for exmaple), in that case how would JSF now which one to use (assuming that each resolver is for a specific kind of expressions)? I tried to make it as an independent question but doesn't seem to me a big matter, so I said maybe you could give me some hint that I can follow. Thanks in advance – Gnarled

@Tarik: they follow decorator pattern (like InputStream and friends). The one registered later wraps/delegates to the previously registered one via super.xxx() call. – Carafe

Answer 2

The work made on this topic is very interesting, but not complete.

In case you pass value in a Composite Component, which is set in this component, it doesn't work.

Example :

<composite:interface>
    <composite:attribute name="value" type="java.lang.Boolean" required="true"  />
</composite:interface>
<composite:implementation>
        <h:inputText id="inputValue" value="#{cc.attrs.value}" 
        </h:inputText>
</composite:implementation>

With the ExtendedBeanElResolver, it throws a PropertyNotFoundException when I set value.

So, I spend few hours to find a solution, and here is the working solution, to be able to use the ExtendedBeanElResolver with the ability to set values inside composite components :

public class ExtendedBeanELResolver extends BeanELResolver {

    private static final String PRIMEFACES_RESOURCE_PREFIX = "primefaces:";
    private static final String RESOURCES_HANDLER = "class org.omnifaces.resourcehandler.GraphicResourceHandler";
    private static final String PRIMEFACES_EXT_RESOURCES_HANDLER = "class org.primefaces.extensions.application.PrimeFacesExtensionsResourceHandler";

    @Override
    public Object getValue(ELContext context, Object base, Object property) {

            if (property == null || base == null || base instanceof ResourceBundle || base instanceof Map || base instanceof Collection
                    || property.toString().startsWith(PRIMEFACES_RESOURCE_PREFIX) || base.getClass().toString().equals(RESOURCES_HANDLER)
                    || base.getClass().toString().equals(PRIMEFACES_EXT_RESOURCES_HANDLER)) {
                return null;
            }
            String propertyString = property.toString();
            if (propertyString.contains(".")) {
                Object value = base;

                for (String propertyPart : propertyString.split("\\.")) {
                    value = super.getValue(context, value, propertyPart);
                }

                return value;
            } else {
                Object v = super.getValue(context, base, property);
               return v;
            }
    }

    @Override
    public void setValue(ELContext context, Object base, Object property, Object val) {
        if (base != null && !(base instanceof ResourceBundle) && !(base instanceof Map) && !(base instanceof Collection))
            super.setValue(context, base, property, val);
    }
}

(I added the "setValue" part).

And now it works. Don't hesitate to give me your feedback, as this is my first post in this website !

Jeana