https://tomcat.apache.org/: JSP package 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.servlet.jsp.tagext;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;


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)
cannot have a SimpleTag as its parent. To remedy this, a TagAdapter is
created to wrap the SimpleTag parent, and the adapter is passed to
setParent() instead. A classic Tag Handler can call getAdaptee() to retrieve
the encapsulated SimpleTag instance.

Since:2.0
/**
 * Wraps any SimpleTag and exposes it using a Tag interface. This is used to
 * allow collaboration between classic Tag handlers and SimpleTag handlers.
 * <p>
 * Because SimpleTag does not extend Tag, and because Tag.setParent() only
 * accepts a Tag instance, a classic tag handler (one that implements Tag)
 * cannot have a SimpleTag as its parent. To remedy this, a TagAdapter is
 * created to wrap the SimpleTag parent, and the adapter is passed to
 * setParent() instead. A classic Tag Handler can call getAdaptee() to retrieve
 * the encapsulated SimpleTag instance.
 *
 * @since 2.0
 */
public class TagAdapter implements Tag {
    
The simple tag that's being adapted. 
/** The simple tag that's being adapted. */
    private final SimpleTag simpleTagAdaptee;

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

Params:
  • adaptee – 
           The SimpleTag being adapted as a Tag.
/**
     * 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.

Params:
  • pc – 
           ignored.
Throws:
/**
     * 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().

Params:
  • parentTag – 
           ignored.
Throws:
/**
     * 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).

Returns:The parent of the tag being adapted.
/**
     * 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();
            if (adapteeParent != null) {
                if (adapteeParent instanceof Tag) {
                    this.parent = (Tag) adapteeParent;
                } else {
                    // Must be SimpleTag - no other types defined.
                    this.parent = new TagAdapter((SimpleTag) adapteeParent);
                }
            }
            parentDetermined = true;
        }

        return this.parent;
    }

    
Gets the tag that is being adapted to the Tag interface. This should be
an instance of SimpleTag in JSP 2.0, but room is left for other kinds of
tags in future spec versions.

Returns:the tag that is being adapted
/**
     * Gets the tag that is being adapted to the Tag interface. This should be
     * an instance of SimpleTag in JSP 2.0, but room is left for other kinds of
     * tags in future spec versions.
     *
     * @return the tag that is being adapted
     */
    public JspTag getAdaptee() {
        return this.simpleTagAdaptee;
    }

    
Must not be called.

Throws:
Returns:always throws UnsupportedOperationException
/**
     * Must not be called.
     *
     * @return always throws UnsupportedOperationException
     * @throws UnsupportedOperationException
     *             Must not be called
     * @throws JspException
     *             never thrown
     */
    @Override
    public int doStartTag() throws JspException {
        throw new UnsupportedOperationException(
                "Illegal to invoke doStartTag() on TagAdapter wrapper");
    }

    
Must not be called.

Throws:
Returns:always throws UnsupportedOperationException
/**
     * Must not be called.
     *
     * @return always throws UnsupportedOperationException
     * @throws UnsupportedOperationException
     *             Must not be called
     * @throws JspException
     *             never thrown
     */
    @Override
    public int doEndTag() throws JspException {
        throw new UnsupportedOperationException(
                "Illegal to invoke doEndTag() on TagAdapter wrapper");
    }

    
Must not be called.

Throws:
  • UnsupportedOperationException – 
            Must not be called
/**
     * Must not be called.
     *
     * @throws UnsupportedOperationException
     *             Must not be called
     */
    @Override
    public void release() {
        throw new UnsupportedOperationException(
                "Illegal to invoke release() on TagAdapter wrapper");
    }
}