Class TagAdapter

java/jakarta/servlet/jsp/tagext/TagAdapter.java:33–150

Wraps any SimpleTag and exposes it using a Tag interface. This is used to allow collaboration between classic Tag handlers and SimpleTag handlers. Because SimpleTag does not extend Tag, and because Tag.setParent() only accepts a Tag instance, a classic tag handler (one that implements Tag) canno

 * @since JSP 2.0
 */
public class TagAdapter implements Tag {
    /** The simple tag that's being adapted. */
    private final SimpleTag simpleTagAdaptee;

    /** The parent, of this tag, converted (if necessary) to be of type Tag. */
    private Tag parent;

    // Flag indicating whether we have already determined the parent
    private boolean parentDetermined;

    /**
     * Creates a new TagAdapter that wraps the given SimpleTag and returns the parent tag when getParent() is called.
     *
     * @param adaptee The SimpleTag being adapted as a Tag.
     */
    public TagAdapter(SimpleTag adaptee) {
        if (adaptee == null) {
            // Cannot wrap a null adaptee.
            throw new IllegalArgumentException();
        }
        this.simpleTagAdaptee = adaptee;
    }

    /**
     * Must not be called.
     *
     * @param pc ignored.
     *
     * @throws UnsupportedOperationException Must not be called
     */
    @Override
    public void setPageContext(PageContext pc) {
        throw new UnsupportedOperationException("Illegal to invoke setPageContext() on TagAdapter wrapper");
    }

    /**
     * Must not be called. The parent of this tag is always getAdaptee().getParent().
     *
     * @param parentTag ignored.
     *
     * @throws UnsupportedOperationException Must not be called.
     */
    @Override
    public void setParent(Tag parentTag) {
        throw new UnsupportedOperationException("Illegal to invoke setParent() on TagAdapter wrapper");
    }

    /**
     * Returns the parent of this tag, which is always getAdaptee().getParent(). This will either be the enclosing Tag
     * (if getAdaptee().getParent() implements Tag), or an adapter to the enclosing Tag (if getAdaptee().getParent()
     * does not implement Tag).
     *
     * @return The parent of the tag being adapted.
     */
    @Override
    public Tag getParent() {
        if (!parentDetermined) {
            JspTag adapteeParent = simpleTagAdaptee.getParent();