javax.servlet.jsp.tagext.TagAdapter Maven / Gradle / Ivy
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package javax.servlet.jsp.tagext;
import javax.servlet.jsp.*;
/**
* 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 JSP 2.0
*/
public class TagAdapter
implements Tag
{
/** The simple tag that's being adapted. */
private 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
*/
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.
*/
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.
*/
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.
*
* @return the tag that is being adapted
*/
public JspTag getAdaptee() {
return this.simpleTagAdaptee;
}
/**
* Must not be called.
*
* @return always throws UnsupportedOperationException
* @throws UnsupportedOperationException Must not be called
* @throws JspException never thrown
*/
public int doStartTag() throws JspException {
throw new UnsupportedOperationException(
"Illegal to invoke doStartTag() on TagAdapter wrapper" );
}
/**
* Must not be called.
*
* @return always throws UnsupportedOperationException
* @throws UnsupportedOperationException Must not be called
* @throws JspException never thrown
*/
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
*/
public void release() {
throw new UnsupportedOperationException(
"Illegal to invoke release() on TagAdapter wrapper" );
}
}