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.

   */
  public int doStartTag()
    throws JspException
  {
    try {
      Tag parent = getParent();


      if (! (parent instanceof ChooseTag))
        throw new JspException(L.l("c:when tag must be contained in a c:choose tag."));


      ChooseTag chooseTag = (ChooseTag) parent;

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   */
  public int doStartTag()
    throws JspException
  {
    try {
      Tag parent = getParent();


      if (! (parent instanceof ChooseTag))
        throw new JspException(L.l("x:when tag must be contained in a c:choose tag."));


      ChooseTag chooseTag = (ChooseTag) parent;

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    PageContextImpl pageContext = (PageContextImpl) this.pageContext;
    
    Object value = _valueExpr.evalObject(pageContext.getELContext());


    Tag parent = getParent();
    for (;
         parent != null && ! (parent instanceof SQLExecutionTag);
         parent = parent.getParent()) {
    }


    if (parent == null)
      throw new JspException(L.l("sql:param requires sql:query parent."));

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      if (name == null)
        return SKIP_BODY;
      
      String value = _valueExpr.evalString(env);
    
      Tag parent = getParent();
      for (; parent != null; parent = parent.getParent()) {
        if (parent instanceof NameValueTag) {
          NameValueTag tag = (NameValueTag) parent;


          if (value == null)
            tag.addParam(name, "");

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   * Process the tag.
   */
  public int doStartTag()
    throws JspException
  {
    Tag parent = getParent();


    if (! (parent instanceof ChooseTag))
      throw new JspException(L.l("c:otherwise tag must be contained in a c:choose tag."));


    ChooseTag chooseTag = (ChooseTag) parent;

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     * @return Reused or newly instantiated tag handler
     *
     * @throws JspException if a tag handler cannot be instantiated
     */
    public Tag get(Class handlerClass) throws JspException {
  Tag handler = null;
        synchronized( this ) {
            if (current >= 0) {
                handler = handlers[current--];
                return handler;
            }
        }


        // Out of sync block - there is no need for other threads to
        // wait for us to construct a tag for this thread.
        try {
            Tag instance = (Tag) handlerClass.newInstance();
            AnnotationHelper.postConstruct(annotationProcessor, instance);
            return instance;
        } catch (Exception e) {
            throw new JspException(e.getMessage(), e);
        }

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              Locale[] avail) {


  LocalizationContext locCtxt = null;
  
  // Get formatting locale from enclosing <fmt:bundle>
  Tag parent = findAncestorWithClass(fromTag, BundleSupport.class);
  if (parent != null) {
      /*
       * use locale from localization context established by parent
       * <fmt:bundle> action, unless that locale is null
       */

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     * @return Reused or newly instantiated tag handler
     *
     * @throws JspException if a tag handler cannot be instantiated
     */
    public Tag get(Class handlerClass) throws JspException {
  Tag handler = null;
        synchronized( this ) {
            if (current >= 0) {
                handler = handlers[current--];
                return handler;
            }
        }


        // Out of sync block - there is no need for other threads to
        // wait for us to construct a tag for this thread.
        try {
            Tag instance = (Tag) handlerClass.newInstance();
            AnnotationHelper.postConstruct(annotationProcessor, instance);
            return instance;
        } catch (Exception e) {
            throw new JspException(e.getMessage(), e);
        }

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     * @exception JspException if a processing error occurs
     */
    public int doEndTag() throws JspException {
        
        // Find our parent TableTag instance
        Tag parent = getParent();
        while ((parent != null) && !(parent instanceof TableTag)) {
            parent = parent.getParent();
        }
        if (parent == null) {
            throw new JspException("Must be nested in a TableTag instance");
        }
        TableTag table = (TableTag) parent;

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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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