Examples of javax.servlet.jsp.tagext.Tag

javax.servlet.jsp.tagext.Tag
The interface of a simple tag handler that does not want to manipulate its body. The Tag interface defines the basic protocol between a Tag handler and JSP page implementation class. It defines the life cycle and the methods to be invoked at start and end tag.
Properties
The Tag interface specifies the setter and getter methods for the core pageContext and parent properties.
The JSP page implementation object invokes setPageContext and setParent, in that order, before invoking doStartTag() or doEndTag().
Methods
There are two main actions: doStartTag and doEndTag. Once all appropriate properties have been initialized, the doStartTag and doEndTag methods can be invoked on the tag handler. Between these invocations, the tag handler is assumed to hold a state that must be preserved. After the doEndTag invocation, the tag handler is available for further invocations (and it is expected to have retained its properties).
Lifecycle
Lifecycle details are described by the transition diagram below, with the following comments:
- [1] This transition is intended to be for releasing long-term data. no guarantees are assumed on whether any properties have been retained or not.
- [2] This transition happens if and only if the tag ends normally without raising an exception
- [3] Note that since there are no guarantees on the state of the properties, a tag handler that had some optional properties set can only be reused if those properties are set to a new (known) value. This means that tag handlers can only be reused within the same "AttSet" (set of attributes that have been set).
- Check the TryCatchFinally interface for additional details related to exception handling and resource management.
Once all invocations on the tag handler are completed, the release method is invoked on it. Once a release method is invoked all properties, including parent and pageContext, are assumed to have been reset to an unspecified value. The page compiler guarantees that release() will be invoked on the Tag handler before the handler is released to the GC.
Empty and Non-Empty Action
If the TagLibraryDescriptor file indicates that the action must always have an empty action, by an <body-content> entry of "empty", then the doStartTag() method must return SKIP_BODY. Otherwise, the doStartTag() method may return SKIP_BODY or EVAL_BODY_INCLUDE.
If SKIP_BODY is returned the body, if present, is not evaluated.
If EVAL_BODY_INCLUDE is returned, the body is evaluated and "passed through" to the current out.

    //*********************************************************************
    // Tag logic


    // simply send our name and value to our appropriate ancestor
    public int doEndTag() throws JspException {
  Tag t = findAncestorWithClass(this, ParamParent.class);
  if (t == null)
      throw new JspTagException(
    Resources.getMessage("PARAM_OUTSIDE_PARENT"));


  // take no action for null or empty names

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     * ChooseTag wants it to do so.  The condition will not even be
     * evaluated if ChooseTag instructs us not to run.
     */
    public int doStartTag() throws JspException {


        Tag parent;


        // make sure we're contained properly
        if (!((parent = getParent()) instanceof ChooseTag))
            throw new JspTagException(
    Resources.getMessage("WHEN_OUTSIDE_CHOOSE"));

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    //*********************************************************************
    // Tag logic


    // Supply our value to our parent <fmt:message> tag
    public int doEndTag() throws JspException {
  Tag t = findAncestorWithClass(this, MessageSupport.class);
  if (t == null) {
      throw new JspTagException(Resources.getMessage(
                            "PARAM_OUTSIDE_MESSAGE"));
  }
  MessageSupport parent = (MessageSupport) t;

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      return EVAL_PAGE;
  }


  String prefix = null;
  if (!bundleSpecified) {
      Tag t = findAncestorWithClass(this, BundleSupport.class);
      if (t != null) {
    // use resource bundle from parent <bundle> tag
    BundleSupport parent = (BundleSupport) t;
    locCtxt = parent.getLocalizationContext();
    prefix = parent.getPrefix();

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        // create the verbatim component if not inside a facet (facets are rendered
        // by their parents) and in a component that renders children
        if (!isFacet())
        {
            Tag parent = getParent();


            // flush if in a loop tag and not in a jsp tag
            if (parent != null && parent instanceof LoopTag)
            {
                JspWriter outWriter = pageContext.getOut();

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        // JSF-Spec 1.2 9.4.9
        // Locate the one and only UIViewRoot custom action instance by walking up the tag tree
        // until you find a UIComponentELTag instance that has no parent. If the
        // getCreated() method of this instance returns true, check the binding attribute.


        Tag parent = this;
        UIComponentELTag parentTag = null;
        while ((parent = parent.getParent()) != null)
        {
            if (parent instanceof UIComponentELTag)
            {
                parentTag = (UIComponentELTag)parent;
            }

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      return null;
    }


    for (;;)
    {
      Tag tag = from.getParent();


      if (tag == null)
      {
        return null;
      }


      if ((isInterface && klass.isInstance(tag))
          || klass.isAssignableFrom(tag.getClass()))
        return tag;
      else
        from = tag;
    }
  }

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   * If so, it returns the facet name on the <f:facet> tag.
   * Otherwise, it returns null.
   */
  private String _getParentFacetName()
  {
    Tag parent = getParent();
    if (parent instanceof FacetTag)
    {
        return (((FacetTag) parent).getName());
    }
    return null;

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public class AntProperty extends TagSupport {
    
    public AntProperty() {}


    public int doStartTag() throws JspException {
  Tag parent=getParent();
  if( parent == null  )
      throw new JspException( "AntProperty used as top-level tag,"+
            "must be inside <ant>");
  if( ! (parent instanceof AntTag))
      throw new JspException( "AntProperty must be child of <ant>");

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public class AntTarget extends TagSupport {
    
    public AntTarget() {}


    public int doStartTag() throws JspException {
  Tag parent=getParent();
  if( parent == null  )
      throw new JspException( "AntTarget used as top-level tag,"+
            "must be inside <ant>");
  if( ! (parent instanceof AntTag ))
      throw new JspException( "AntTarget must be child of <ant>");

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