core/src/main/java/org/apache/commons/digester3/Rule.java

package org.apache.commons.digester3;

/*
 * 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.
 */

import org.xml.sax.Attributes;

/**
 * Concrete implementations of this class implement actions to be taken when a
 * corresponding nested pattern of XML elements has been matched.
 * <p>
 * Writing a custom Rule is considered perfectly normal when using Digester, and
 * is encouraged whenever the default set of Rule classes don't meet your
 * requirements; the digester framework can help process xml even when the
 * built-in rules aren't quite what is needed. Creating a custom Rule is just as
 * easy as subclassing javax.servlet.http.HttpServlet for webapps, or
 * javax.swing.Action for GUI applications.
 * <p>
 * If a rule wishes to manipulate a digester stack (the default object stack, a
 * named stack, or the parameter stack) then it should only ever push objects in
 * the rule's begin method and always pop exactly the same number of objects off
 * the stack during the rule's end method. Of course peeking at the objects on
 * the stacks can be done from anywhere.
 * <p>
 * Rule objects should limit their state data to the digester object stack and
 * named stacks. Storing state in instance fields (other than digester) during
 * the parsing process will cause problems if invoked in a "nested" manner; this
 * can happen if the same instance is added to digester multiple times or if a
 * wildcard pattern is used which can match both an element and a child of the
 * same element.
 * <p>
 * Rule objects are not thread-safe when each thread creates a new digester, as
 * is commonly the case. In a multithreaded context you should create new Rule
 * instances for every digester or synchronize read/write access to the digester
 * within the Rule.
 */public abstract class Rule
{

    // ----------------------------------------------------- Instance Variables

    /**
     * The Digester with which this Rule is associated.
     */
    private Digester digester = null;

    /**
     * The namespace URI for which this Rule is relevant, if any.
     */
    private String namespaceURI = null;

    // ------------------------------------------------------------- Properties

    /**
     * Return the Digester with which this Rule is associated.
     *
     * @return the Digester with which this Rule is associated
     */
    public Digester getDigester()
    {
        return ( this.digester );
    }

    /**
     * Set the <code>Digester</code> with which this <code>Rule</code> is associated.
     *
     * @param digester the <code>Digester</code> with which this <code>Rule</code> is associated
     */
    public void setDigester( Digester digester )
    {
        this.digester = digester;
    }

    /**
     * Return the namespace URI for which this Rule is relevant, if any.
     *
     * @return the namespace URI for which this Rule is relevant, if any
     */
    public String getNamespaceURI()
    {
        return ( this.namespaceURI );
    }

    /**
     * Set the namespace URI for which this Rule is relevant, if any.
     *
     * @param namespaceURI Namespace URI for which this Rule is relevant, or <code>null</code> to match independent of
     *            namespace.
     */
    public void setNamespaceURI( String namespaceURI )
    {
        this.namespaceURI = namespaceURI;
    }

    // --------------------------------------------------------- Public Methods

    /**
     * This method is called when the beginning of a matching XML element is encountered.
     *
     * @param namespace the namespace URI of the matching element, or an empty string if the parser is not namespace
     *            aware or the element has no namespace
     * @param name the local name if the parser is namespace aware, or just the element name otherwise
     * @param attributes The attribute list of this element
     * @throws Exception if any error occurs
     * @since Digester 1.4
     */
    public void begin( String namespace, String name, Attributes attributes )
        throws Exception
    {
        // The default implementation does nothing
    }

    /**
     * This method is called when the body of a matching XML element is encountered. If the element has no body, this
     * method is called with an empty string as the body text.
     *
     * @param namespace the namespace URI of the matching element, or an empty string if the parser is not namespace
     *            aware or the element has no namespace
     * @param name the local name if the parser is namespace aware, or just the element name otherwise
     * @param text The text of the body of this element
     * @throws Exception if any error occurs
     * @since Digester 1.4
     */
    public void body( String namespace, String name, String text )
        throws Exception
    {
        // The default implementation does nothing
    }

    /**
     * This method is called when the end of a matching XML element is encountered.
     *
     * @param namespace the namespace URI of the matching element, or an empty string if the parser is not namespace
     *            aware or the element has no namespace
     * @param name the local name if the parser is namespace aware, or just the element name otherwise
     * @throws Exception if any error occurs
     * @since Digester 1.4
     */
    public void end( String namespace, String name )
        throws Exception
    {
        // The default implementation does nothing
    }

    /**
     * This method is called after all parsing methods have been called, to allow Rules to remove temporary data.
     *
     * @throws Exception if any error occurs
     */
    public void finish()
        throws Exception
    {
        // The default implementation does nothing
    }

}