JSF2: limiting cc:attribute to a given object type within a List

问题

If I had a managed bean as follows:

@ManagedBean
@RequestSchoped
public class Example {

    private List<String> stringList;
    private List<Long> longList;

    // getters, setters, etc. down here
}

and had a custom component which accepted a List as an attribute:

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:cc="http://java.sun.com/jsf/composite"
      xmlns:h="http://java.sun.com/jsf/html">

  <!-- INTERFACE -->
  <cc:interface>
      <cc:attribute name="aList" type="java.util.List" />
  </cc:interface>

  <cc:implementation>
      <!-- code is in here -->
  </cc:implementation>
</html>

How could I make sure that this worked:

<myComp:previousComponent aList="#{example.stringList}" />

but this didn't:

<myComp:previousComponent aList="#{example.longList}" />

In other words, what I want to do for the cc:attribute is as follows:

<cc:attribute name="aList" type="java.util.List<java.lang.String>" />

However, as we know xhtml doesn't take kindly to using > or <. Also, with Generics only being checked at compile time, I'm not sure how this would be done. Does anyone know if this is possible?

回答1:

You could check the type of each item using #{item.class.name}. The Class#getName() returns a String denoting the type. E.g. java.lang.String or java.lang.Long. You could make use of it in the rendered attribute.

Add an extra attribute denoting the full qualified classname.

<my:comp list="#{bean.list}" type="java.lang.String" />

in combination with

<cc:attribute name="list" type="java.util.List" required="true" />
<cc:attribute name="type" type="java.util.String" required="true" />

and this logic in cc:implementation:

<ul>
    <ui:repeat value="#{cc.attrs.list}" var="item">
        <h:panelGroup rendered="#{item.class.name == cc.attrs.type}">
            <li>#{item}</li>
        </h:panelGroup>
    </ui:repeat>
</ul>

回答2:

If you are the one producing these lists then the following could be a trivial solution:

interface StringList extends List<String> {}

class ArrayStringList extends ArrayList<String> implements StringList {}

Not too elegant though.

I think we have reached the boundaries of the Java language here. I have encountered the same problem, and couldn't find a better solution either...

来源：https://stackoverflow.com/questions/3113603/jsf2-limiting-ccattribute-to-a-given-object-type-within-a-list

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xhtml

jsf

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jsf-2

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