jakarta.servlet.jsp.tagext.SimpleTagSupport Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2020 Oracle and/or its affiliates and others.
* All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* Licensed 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 jakarta.servlet.jsp.tagext;
import jakarta.servlet.jsp.JspContext;
import jakarta.servlet.jsp.JspException;
import java.io.IOException;
/**
* A base class for defining tag handlers implementing SimpleTag.
*
* The SimpleTagSupport class is a utility class intended to be used as the base class for new simple tag handlers. The
* SimpleTagSupport class implements the SimpleTag interface and adds additional convenience methods including getter
* methods for the properties in SimpleTag.
*
* @since JSP 2.0
*/
public class SimpleTagSupport implements SimpleTag {
/** Reference to the enclosing tag. */
private JspTag parentTag;
/** The JSP context for the upcoming tag invocation. */
private JspContext jspContext;
/** The body of the tag. */
private JspFragment jspBody;
/**
* Sole constructor. (For invocation by subclass constructors, typically implicit.)
*/
public SimpleTagSupport() {
}
/**
* Default processing of the tag does nothing.
*
* @throws JspException Subclasses can throw JspException to indicate an error occurred while processing this tag.
* @throws jakarta.servlet.jsp.SkipPageException If the page that (either directly or indirectly) invoked
* this tag is to cease evaluation. A Simple Tag Handler generated from a tag file must throw
* this exception if an invoked Classic Tag Handler returned SKIP_PAGE or if an invoked Simple
* Tag Handler threw SkipPageException or if an invoked Jsp Fragment threw a SkipPageException.
* @throws IOException Subclasses can throw IOException if there was an error writing to the output stream
* @see SimpleTag#doTag()
*/
@Override
public void doTag() throws JspException, IOException {
}
/**
* Sets the parent of this tag, for collaboration purposes.
*
* The container invokes this method only if this tag invocation is nested within another tag invocation.
*
* @param parent the tag that encloses this tag
*/
@Override
public void setParent(JspTag parent) {
this.parentTag = parent;
}
/**
* Returns the parent of this tag, for collaboration purposes.
*
* @return the parent of this tag
*/
@Override
public JspTag getParent() {
return this.parentTag;
}
/**
* Stores the provided JSP context in the private jspContext field. Subclasses can access the
* JspContext via getJspContext().
*
* @param pc the page context for this invocation
* @see SimpleTag#setJspContext
*/
@Override
public void setJspContext(JspContext pc) {
this.jspContext = pc;
}
/**
* Returns the page context passed in by the container via setJspContext.
*
* @return the page context for this invocation
*/
protected JspContext getJspContext() {
return this.jspContext;
}
/**
* Stores the provided JspFragment.
*
* @param jspBody The fragment encapsulating the body of this tag. If the action element is empty in the page, this
* method is not called at all.
* @see SimpleTag#setJspBody
*/
@Override
public void setJspBody(JspFragment jspBody) {
this.jspBody = jspBody;
}
/**
* Returns the body passed in by the container via setJspBody.
*
* @return the fragment encapsulating the body of this tag, or null if the action element is empty in the page.
*/
protected JspFragment getJspBody() {
return this.jspBody;
}
/**
* Find the instance of a given class type that is closest to a given instance. This method uses the getParent
* method from the Tag and/or SimpleTag interfaces. This method is used for coordination among cooperating tags.
*
*
* For every instance of TagAdapter encountered while traversing the ancestors, the tag handler returned by
* TagAdapter.getAdaptee() - instead of the TagAdpater itself - is compared to klass. If the tag
* handler matches, it - and not its TagAdapter - is returned.
*
*
* The current version of the specification only provides one formal way of indicating the observable type of a tag
* handler: its tag handler implementation class, described in the tag-class subelement of the tag element. This is
* extended in an informal manner by allowing the tag library author to indicate in the description subelement an
* observable type. The type should be a subtype of the tag handler implementation class or void. This addititional
* constraint can be exploited by a specialized container that knows about that specific tag library, as in the case
* of the JSP standard tag library.
*
*
* When a tag library author provides information on the observable type of a tag handler, client programmatic code
* should adhere to that constraint. Specifically, the Class passed to findAncestorWithClass should be a subtype of
* the observable type.
*
*
* @param from The instance from where to start looking.
* @param klass The subclass of JspTag or interface to be matched
* @return the nearest ancestor that implements the interface or is an instance of the class specified
*/
public static final JspTag findAncestorWithClass(JspTag from, Class klass) {
boolean isInterface = false;
if (from == null || klass == null
|| (!JspTag.class.isAssignableFrom(klass) && !(isInterface = klass.isInterface()))) {
return null;
}
for (;;) {
JspTag parent = null;
if (from instanceof SimpleTag) {
parent = ((SimpleTag) from).getParent();
} else if (from instanceof Tag) {
parent = ((Tag) from).getParent();
}
if (parent == null) {
return null;
}
if (parent instanceof TagAdapter) {
parent = ((TagAdapter) parent).getAdaptee();
}
if ((isInterface && klass.isInstance(parent)) || klass.isAssignableFrom(parent.getClass())) {
return parent;
}
from = parent;
}
}
}