001/*
002 * Copyright 2002-2012 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.beans.factory.xml;
018
019import org.w3c.dom.Element;
020import org.w3c.dom.Node;
021
022import org.springframework.beans.factory.config.BeanDefinition;
023import org.springframework.beans.factory.config.BeanDefinitionHolder;
024import org.springframework.lang.Nullable;
025
026/**
027 * Base interface used by the {@link DefaultBeanDefinitionDocumentReader}
028 * for handling custom namespaces in a Spring XML configuration file.
029 *
030 * <p>Implementations are expected to return implementations of the
031 * {@link BeanDefinitionParser} interface for custom top-level tags and
032 * implementations of the {@link BeanDefinitionDecorator} interface for
033 * custom nested tags.
034 *
035 * <p>The parser will call {@link #parse} when it encounters a custom tag
036 * directly under the {@code <beans>} tags and {@link #decorate} when
037 * it encounters a custom tag directly under a {@code <bean>} tag.
038 *
039 * <p>Developers writing their own custom element extensions typically will
040 * not implement this interface directly, but rather make use of the provided
041 * {@link NamespaceHandlerSupport} class.
042 *
043 * @author Rob Harrop
044 * @author Erik Wiersma
045 * @since 2.0
046 * @see DefaultBeanDefinitionDocumentReader
047 * @see NamespaceHandlerResolver
048 */
049public interface NamespaceHandler {
050
051        /**
052         * Invoked by the {@link DefaultBeanDefinitionDocumentReader} after
053         * construction but before any custom elements are parsed.
054         * @see NamespaceHandlerSupport#registerBeanDefinitionParser(String, BeanDefinitionParser)
055         */
056        void init();
057
058        /**
059         * Parse the specified {@link Element} and register any resulting
060         * {@link BeanDefinition BeanDefinitions} with the
061         * {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
062         * that is embedded in the supplied {@link ParserContext}.
063         * <p>Implementations should return the primary {@code BeanDefinition}
064         * that results from the parse phase if they wish to be used nested
065         * inside (for example) a {@code <property>} tag.
066         * <p>Implementations may return {@code null} if they will
067         * <strong>not</strong> be used in a nested scenario.
068         * @param element the element that is to be parsed into one or more {@code BeanDefinitions}
069         * @param parserContext the object encapsulating the current state of the parsing process
070         * @return the primary {@code BeanDefinition} (can be {@code null} as explained above)
071         */
072        @Nullable
073        BeanDefinition parse(Element element, ParserContext parserContext);
074
075        /**
076         * Parse the specified {@link Node} and decorate the supplied
077         * {@link BeanDefinitionHolder}, returning the decorated definition.
078         * <p>The {@link Node} may be either an {@link org.w3c.dom.Attr} or an
079         * {@link Element}, depending on whether a custom attribute or element
080         * is being parsed.
081         * <p>Implementations may choose to return a completely new definition,
082         * which will replace the original definition in the resulting
083         * {@link org.springframework.beans.factory.BeanFactory}.
084         * <p>The supplied {@link ParserContext} can be used to register any
085         * additional beans needed to support the main definition.
086         * @param source the source element or attribute that is to be parsed
087         * @param definition the current bean definition
088         * @param parserContext the object encapsulating the current state of the parsing process
089         * @return the decorated definition (to be registered in the BeanFactory),
090         * or simply the original bean definition if no decoration is required.
091         * A {@code null} value is strictly speaking invalid, but will be leniently
092         * treated like the case where the original bean definition gets returned.
093         */
094        @Nullable
095        BeanDefinitionHolder decorate(Node source, BeanDefinitionHolder definition, ParserContext parserContext);
096
097}