001/*
002 * Copyright 2002-2018 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 java.io.IOException;
020import java.util.Map;
021import java.util.Properties;
022import java.util.concurrent.ConcurrentHashMap;
023
024import org.apache.commons.logging.Log;
025import org.apache.commons.logging.LogFactory;
026
027import org.springframework.beans.BeanUtils;
028import org.springframework.beans.FatalBeanException;
029import org.springframework.core.io.support.PropertiesLoaderUtils;
030import org.springframework.util.Assert;
031import org.springframework.util.ClassUtils;
032import org.springframework.util.CollectionUtils;
033
034/**
035 * Default implementation of the {@link NamespaceHandlerResolver} interface.
036 * Resolves namespace URIs to implementation classes based on the mappings
037 * contained in mapping file.
038 *
039 * <p>By default, this implementation looks for the mapping file at
040 * {@code META-INF/spring.handlers}, but this can be changed using the
041 * {@link #DefaultNamespaceHandlerResolver(ClassLoader, String)} constructor.
042 *
043 * @author Rob Harrop
044 * @author Juergen Hoeller
045 * @since 2.0
046 * @see NamespaceHandler
047 * @see DefaultBeanDefinitionDocumentReader
048 */
049public class DefaultNamespaceHandlerResolver implements NamespaceHandlerResolver {
050
051        /**
052         * The location to look for the mapping files. Can be present in multiple JAR files.
053         */
054        public static final String DEFAULT_HANDLER_MAPPINGS_LOCATION = "META-INF/spring.handlers";
055
056
057        /** Logger available to subclasses */
058        protected final Log logger = LogFactory.getLog(getClass());
059
060        /** ClassLoader to use for NamespaceHandler classes */
061        private final ClassLoader classLoader;
062
063        /** Resource location to search for */
064        private final String handlerMappingsLocation;
065
066        /** Stores the mappings from namespace URI to NamespaceHandler class name / instance */
067        private volatile Map<String, Object> handlerMappings;
068
069
070        /**
071         * Create a new {@code DefaultNamespaceHandlerResolver} using the
072         * default mapping file location.
073         * <p>This constructor will result in the thread context ClassLoader being used
074         * to load resources.
075         * @see #DEFAULT_HANDLER_MAPPINGS_LOCATION
076         */
077        public DefaultNamespaceHandlerResolver() {
078                this(null, DEFAULT_HANDLER_MAPPINGS_LOCATION);
079        }
080
081        /**
082         * Create a new {@code DefaultNamespaceHandlerResolver} using the
083         * default mapping file location.
084         * @param classLoader the {@link ClassLoader} instance used to load mapping resources
085         * (may be {@code null}, in which case the thread context ClassLoader will be used)
086         * @see #DEFAULT_HANDLER_MAPPINGS_LOCATION
087         */
088        public DefaultNamespaceHandlerResolver(ClassLoader classLoader) {
089                this(classLoader, DEFAULT_HANDLER_MAPPINGS_LOCATION);
090        }
091
092        /**
093         * Create a new {@code DefaultNamespaceHandlerResolver} using the
094         * supplied mapping file location.
095         * @param classLoader the {@link ClassLoader} instance used to load mapping resources
096         * may be {@code null}, in which case the thread context ClassLoader will be used)
097         * @param handlerMappingsLocation the mapping file location
098         */
099        public DefaultNamespaceHandlerResolver(ClassLoader classLoader, String handlerMappingsLocation) {
100                Assert.notNull(handlerMappingsLocation, "Handler mappings location must not be null");
101                this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
102                this.handlerMappingsLocation = handlerMappingsLocation;
103        }
104
105
106        /**
107         * Locate the {@link NamespaceHandler} for the supplied namespace URI
108         * from the configured mappings.
109         * @param namespaceUri the relevant namespace URI
110         * @return the located {@link NamespaceHandler}, or {@code null} if none found
111         */
112        @Override
113        public NamespaceHandler resolve(String namespaceUri) {
114                Map<String, Object> handlerMappings = getHandlerMappings();
115                Object handlerOrClassName = handlerMappings.get(namespaceUri);
116                if (handlerOrClassName == null) {
117                        return null;
118                }
119                else if (handlerOrClassName instanceof NamespaceHandler) {
120                        return (NamespaceHandler) handlerOrClassName;
121                }
122                else {
123                        String className = (String) handlerOrClassName;
124                        try {
125                                Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
126                                if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
127                                        throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
128                                                        "] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
129                                }
130                                NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
131                                namespaceHandler.init();
132                                handlerMappings.put(namespaceUri, namespaceHandler);
133                                return namespaceHandler;
134                        }
135                        catch (ClassNotFoundException ex) {
136                                throw new FatalBeanException("NamespaceHandler class [" + className + "] for namespace [" +
137                                                namespaceUri + "] not found", ex);
138                        }
139                        catch (LinkageError err) {
140                                throw new FatalBeanException("Invalid NamespaceHandler class [" + className + "] for namespace [" +
141                                                namespaceUri + "]: problem with handler class file or dependent class", err);
142                        }
143                }
144        }
145
146        /**
147         * Load the specified NamespaceHandler mappings lazily.
148         */
149        private Map<String, Object> getHandlerMappings() {
150                Map<String, Object> handlerMappings = this.handlerMappings;
151                if (handlerMappings == null) {
152                        synchronized (this) {
153                                handlerMappings = this.handlerMappings;
154                                if (handlerMappings == null) {
155                                        if (logger.isDebugEnabled()) {
156                                                logger.debug("Loading NamespaceHandler mappings from [" + this.handlerMappingsLocation + "]");
157                                        }
158                                        try {
159                                                Properties mappings =
160                                                                PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
161                                                if (logger.isDebugEnabled()) {
162                                                        logger.debug("Loaded NamespaceHandler mappings: " + mappings);
163                                                }
164                                                handlerMappings = new ConcurrentHashMap<String, Object>(mappings.size());
165                                                CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
166                                                this.handlerMappings = handlerMappings;
167                                        }
168                                        catch (IOException ex) {
169                                                throw new IllegalStateException(
170                                                                "Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
171                                        }
172                                }
173                        }
174                }
175                return handlerMappings;
176        }
177
178
179        @Override
180        public String toString() {
181                return "NamespaceHandlerResolver using mappings " + getHandlerMappings();
182        }
183
184}