Custom tag lib with output parameter

Question

Hi,
I need a tag libray that gives me a specific element of a Vector.
Here there is the line I have in my jsp.
<ct:partizione tronco="${contenitoreCentralineTronco}" indice="index" partizione="tmpPartizione"/>
...-contenitoreCentralineTronco is an Object that contains a Vector of other specif objects.
-indice is the vector index of the specif instance I need.
-partizione should be the output instance.
This is part of my tld file:
    <tag>
         <name>partizione</name>
        <tagclass>ss.aspi.classi.centraline.grafica.tagSupport.Partizione</tagclass>
        <bodycontent>empty</bodycontent>
        <info>Estrae una partizione da un vettore di partizioni dato l'indice</info>
        <attribute>
            <name>tronco</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>indice</name>
            <required>true</required>
        </attribute>
        <attribute>
            <name>partizione</name>
            <required>false</required>
        </attribute>
     </tag>
...this is part of the class called by the tag:
     private ContenitoreTroncoBean tronco;
     private Integer indice;
     private ContenitorePartizioneBean partizione;
     public int doStartTag() throws JspException {
          try {
               Vector<ContenitorePartizioneBean> partizioni = tronco.getPartizioniBean();
               partizione = partizioni.get(indice);
          }catch (Exception e) {
               log.error("Errore nell'estrazione della Partizione "+indice);
               e.printStackTrace();
          return TagSupport.SKIP_BODY;
     //All getter and setter functionsWhen I run the application I get this exception:
jsp.error.beans.property.conversion
looking deeper in the class code jenerated from the jsp, I noted that the problem refers to the third attribute of the tag <ct:partizione>.
It seems It trys to set the attribute "partizione" with the value "tmpPartizione", but partizioni should be an output attribut non input. The varible tmpPartizione doesn't exist... the tag should create it.
I realized I didn't get how I should create a tag with output parameters.
Anyone can explane me it?
Thanks.

Answer 1

One suggestion: Take a closer look at the EL (expression language)
It has an excellent syntax for accessing collections/maps
${contenitoreCentralineTronco[index]} would exactly what you want, without having to write a custom tag for it.
If you REALLY want to do this as a custom tag, then you need to treat the input attribute as a String (the name of the variable you are going to create?) Right now your tag declares the attribute partizione as being of type ContenitorePartizioneBean which is probably the cause of the problem - you are passing it a String.
Cheers,
evnafets