TagSupport.java
/*
* 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 java.io.Serializable;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
/**
* A base class for defining new tag handlers implementing Tag.
* <p>
* The TagSupport class is a utility class intended to be used as the base class for new tag handlers. The TagSupport
* class implements the Tag and IterationTag interfaces and adds additional convenience methods including getter methods
* for the properties in Tag. TagSupport has one static method that is included to facilitate coordination among
* cooperating tags.
* <p>
* Many tag handlers will extend TagSupport and only redefine a few methods.
*/
public class TagSupport implements IterationTag, Serializable {
private static final long serialVersionUID = 1L;
/**
* Find the instance of a given class type that is closest to a given instance. This method uses the getParent
* method from the Tag interface. This method is used for coordination among cooperating tags.
* <p>
* 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 additional
* 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.
* <p>
* 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 Tag or interface to be matched
*
* @return the nearest ancestor that implements the interface or is an instance of the class specified
*/
public static final Tag findAncestorWithClass(Tag from,
// TCK signature test fails with generics
@SuppressWarnings("rawtypes") Class klass) {
boolean isInterface = false;
if (from == null || klass == null ||
(!Tag.class.isAssignableFrom(klass) && !(isInterface = klass.isInterface()))) {
return null;
}
for (;;) {
Tag tag = from.getParent();
if (tag == null) {
return null;
}
if ((isInterface && klass.isInstance(tag)) || ((Class<?>) klass).isAssignableFrom(tag.getClass())) {
return tag;
}
from = tag;
}
}
/**
* Default constructor, all subclasses are required to define only a public constructor with the same signature, and
* to call the superclass constructor. This constructor is called by the code generated by the JSP translator.
*/
public TagSupport() {
// NOOP by default
}
/**
* Default processing of the start tag, returning SKIP_BODY.
*
* @return SKIP_BODY
*
* @throws JspException if an error occurs while processing this tag
*
* @see Tag#doStartTag()
*/
@Override
public int doStartTag() throws JspException {
return SKIP_BODY;
}
/**
* Default processing of the end tag returning EVAL_PAGE.
*
* @return EVAL_PAGE
*
* @throws JspException if an error occurs while processing this tag
*
* @see Tag#doEndTag()
*/
@Override
public int doEndTag() throws JspException {
return EVAL_PAGE;
}
/**
* Default processing for a body.
*
* @return SKIP_BODY
*
* @throws JspException if an error occurs while processing this tag
*
* @see IterationTag#doAfterBody()
*/
@Override
public int doAfterBody() throws JspException {
return SKIP_BODY;
}
// Actions related to body evaluation
/**
* Release state.
*
* @see Tag#release()
*/
@Override
public void release() {
parent = null;
id = null;
if (values != null) {
values.clear();
}
values = null;
}
/**
* Set the nesting tag of this tag.
*
* @param t The parent Tag.
*
* @see Tag#setParent(Tag)
*/
@Override
public void setParent(Tag t) {
parent = t;
}
/**
* The Tag instance most closely enclosing this tag instance.
*
* @see Tag#getParent()
*
* @return the parent tag instance or null
*/
@Override
public Tag getParent() {
return parent;
}
/**
* Set the id attribute for this tag.
*
* @param id The String for the id.
*/
public void setId(String id) {
this.id = id;
}
/**
* The value of the id attribute of this tag; or null.
*
* @return the value of the id attribute, or null
*/
public String getId() {
return id;
}
/**
* Set the page context.
*
* @param pageContext The PageContext.
*
* @see Tag#setPageContext
*/
@Override
public void setPageContext(PageContext pageContext) {
this.pageContext = pageContext;
}
/**
* Associate a value with a String key.
*
* @param k The key String.
* @param o The value to associate.
*/
public void setValue(String k, Object o) {
if (values == null) {
values = new ConcurrentHashMap<>();
}
values.put(k, o);
}
/**
* Get a the value associated with a key.
*
* @param k The string key.
*
* @return The value associated with the key, or null.
*/
public Object getValue(String k) {
if (values == null) {
return null;
}
return values.get(k);
}
/**
* Remove a value associated with a key.
*
* @param k The string key.
*/
public void removeValue(String k) {
if (values != null) {
values.remove(k);
}
}
/**
* Enumerate the keys for the values kept by this tag handler.
*
* @return An enumeration of all the keys for the values set, or null or an empty Enumeration if no values have been
* set.
*/
public Enumeration<String> getValues() {
if (values == null) {
return null;
}
return Collections.enumeration(values.keySet());
}
/**
* The parent, if any, of this tag.
*/
private Tag parent;
/**
* Map of object values keyed by Strings for this tag.
*/
private Map<String,Object> values;
/**
* The value of the id attribute of this tag; or null.
*/
protected String id;
/**
* The PageContext.
*/
protected transient PageContext pageContext;
}