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package javax.faces.webapp;

import javax.faces.component.UIComponent;
import javax.faces.component.ValueHolder;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
import javax.faces.convert.ConverterException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;






/**
 * <p><strong>ConverterELTag</strong> is a base class for all JSP custom
 * actions that create and register a <code>Converter</code> instance on
 * the {@link ValueHolder} associated with our most immediate
 * surrounding instance of a tag whose implementation class is a
 * subclass of {@link UIComponentClassicTagBase}.  To avoid creating duplicate
 * instances when a page is redisplayed, creation and registration of a
 * {@link Converter} occurs <strong>only</strong> if the corresponding
 * {@link UIComponent} was created (by the owning {@link
 * UIComponentTag}) during the execution of the current page.</p>
 *
 * <p>This class may be used as a base class for tag instances that
 * support specific {@link Converter} subclasses.</p>
 *
 * <p>Subclasses of this class must implement the
 * <code>createConverter()</code> method, which creates and returns a
 * {@link Converter} instance.  Any configuration properties that specify
 * behavior of this {@link Converter} must have been set by the
 * <code>createConverter()</code> method.  Generally, this occurs
 * by copying corresponding attribute values on the tag instance.</p>
 *
 * <p>This tag creates no output to the page currently being created.  It
 * is used solely for the side effect of {@link Converter} creation.</p>
 *
 */

public abstract class ConverterELTag extends TagSupport {


    // ---------------------------------------------------------- Public Methods


    /**
     * <p>Create a new instance of the specified {@link Converter}
     * class, and register it with the {@link UIComponent} instance associated
     * with our most immediately surrounding {@link UIComponentClassicTagBase} instance, if
     * the {@link UIComponent} instance was created by this execution of the
     * containing JSP page.  If the localValue of the
     * {@link UIComponent} is a String, attempt to convert it.</p></p>
     *
     * @throws JspException if a JSP error occurs
     */
    public int doStartTag() throws JspException {

        // Locate our parent UIComponentTag
        UIComponentClassicTagBase tag =
             UIComponentClassicTagBase.getParentUIComponentClassicTagBase(pageContext);
        if (tag == null) { // PENDING - i18n
            throw new JspException("Not nested in a UIComponentTag Error for tag with handler class:"+
                    this.getClass().getName());
        }

        // Nothing to do unless this tag created a component
        if (!tag.getCreated()) {
            return (SKIP_BODY);
        }

        UIComponent component = tag.getComponentInstance();
        if (component == null) {            
            //PENDING i18n
            throw new JspException("Can't create Component from tag.");
        }
        if (!(component instanceof ValueHolder)) {
            //PENDING i18n
            throw new JspException("Not nested in a tag of proper type. Error for tag with handler class:"+
                    this.getClass().getName());
        }
        
        Converter converter = createConverter();
        
        if (converter == null) {
            throw new JspException("Can't create class of type:"+
                    " javax.faces.convert.Converter, converter is null");
        }
        
        ValueHolder vh = (ValueHolder)component;
        FacesContext context = FacesContext.getCurrentInstance();
        
        // Register an instance with the appropriate component
        vh.setConverter(converter);
        
        // Once the converter has been set, attempt to convert the
        // incoming "value"
        Object localValue = vh.getLocalValue();
        if (localValue instanceof String) {
            try {
                localValue = converter.getAsObject(context, (UIComponent)vh, (String) localValue);
                vh.setValue(localValue);
            }
            catch (ConverterException ce) {
                // PENDING - Ignore?  Throw an exception?  Set the local
                // value back to "null" and log a warning?
            }
        }        
  
        return (SKIP_BODY);

    }


    // ------------------------------------------------------- Protected Methods


    /**
     * <p>Create and return a new {@link Converter} to be registered
     * on our surrounding {@link UIComponent}.</p>
     *
     * @throws JspException if a new instance cannot be created
     */
    protected abstract Converter createConverter()
        throws JspException;
}
