/*
* #!
* Ontopia Navigator
* #-
* Copyright (C) 2001 - 2013 The Ontopia Project
* #-
* 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 net.ontopia.topicmaps.nav2.taglibs.value;
import java.util.HashSet;
import java.util.Collection;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.tagext.TagSupport;
import net.ontopia.topicmaps.nav2.core.ValueProducingTagIF;
import net.ontopia.topicmaps.nav2.core.ValueAcceptingTagIF;
/**
* INTERNAL: Value Producing Tag for computing
* the set difference of two collections.
*/
public class DifferenceTag extends TagSupport implements ValueAcceptingTagIF {
// members
private Collection resultCollection;
/**
* Process the start tag for this instance.
*/
public int doStartTag() {
// evaluate body
return EVAL_BODY_INCLUDE;
}
/**
* Process the end tag.
*/
public int doEndTag() {
// retrieve parent tag which accepts the produced collection by this tag
ValueAcceptingTagIF acceptingTag = (ValueAcceptingTagIF)
findAncestorWithClass(this, ValueAcceptingTagIF.class);
// kick it over to the accepting tag
acceptingTag.accept( resultCollection );
// reset member collection
resultCollection = null;
return EVAL_PAGE;
}
/**
* reset the state of the Tag.
*/
public void release() {
// overwrite default behaviour
// do not set parent to null!!!
}
// -----------------------------------------------------------------
// Implementation of ValueAcceptingTagIF
// -----------------------------------------------------------------
public void accept(Collection inputCollection) {
if (resultCollection == null) {
// setup first collection
resultCollection = new HashSet(inputCollection);
} else {
// calculate difference between first and second collection
resultCollection.removeAll(inputCollection);
}
}
}