001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.activemq.filter;
018    
019    import java.io.IOException;
020    import java.lang.reflect.Constructor;
021    import java.lang.reflect.InvocationTargetException;
022    import java.util.ArrayList;
023    import java.util.List;
024    import java.util.Map;
025    import java.util.Properties;
026    
027    import javax.jms.JMSException;
028    import javax.xml.parsers.DocumentBuilder;
029    import javax.xml.parsers.DocumentBuilderFactory;
030    import javax.xml.parsers.ParserConfigurationException;
031    
032    import org.apache.activemq.command.Message;
033    import org.apache.activemq.util.JMSExceptionSupport;
034    import org.slf4j.Logger;
035    import org.slf4j.LoggerFactory;
036    
037    /**
038     * Used to evaluate an XPath Expression in a JMS selector.
039     */
040    public final class XPathExpression implements BooleanExpression {
041    
042        private static final Logger LOG = LoggerFactory.getLogger(XPathExpression.class);
043        private static final String EVALUATOR_SYSTEM_PROPERTY = "org.apache.activemq.XPathEvaluatorClassName";
044        private static final String DEFAULT_EVALUATOR_CLASS_NAME = XalanXPathEvaluator.class.getName();
045        public static final String DOCUMENT_BUILDER_FACTORY_FEATURE = "org.apache.activemq.documentBuilderFactory.feature";
046    
047        private static final Constructor EVALUATOR_CONSTRUCTOR;
048        private static DocumentBuilder builder = null;
049    
050        static {
051            String cn = System.getProperty(EVALUATOR_SYSTEM_PROPERTY, DEFAULT_EVALUATOR_CLASS_NAME);
052            Constructor m = null;
053            try {
054                try {
055                    m = getXPathEvaluatorConstructor(cn);
056                    DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
057                    builderFactory.setNamespaceAware(true);
058                    builderFactory.setIgnoringElementContentWhitespace(true);
059                    builderFactory.setIgnoringComments(true);
060                    try {
061                        // set some reasonable defaults
062                        builderFactory.setFeature("http://xml.org/sax/features/external-general-entities", false);
063                        builderFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
064                        builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
065                    } catch (ParserConfigurationException e) {
066                        LOG.warn("Error setting document builder factory feature", e);
067                    }
068                    // setup the feature from the system property
069                    setupFeatures(builderFactory);
070                    builder = builderFactory.newDocumentBuilder();
071                } catch (Throwable e) {
072                    LOG.warn("Invalid " + XPathEvaluator.class.getName() + " implementation: " + cn + ", reason: " + e, e);
073                    cn = DEFAULT_EVALUATOR_CLASS_NAME;
074                    try {
075                        m = getXPathEvaluatorConstructor(cn);
076                    } catch (Throwable e2) {
077                        LOG.error("Default XPath evaluator could not be loaded", e);
078                    }
079                }
080            } finally {
081                EVALUATOR_CONSTRUCTOR = m;
082            }
083        }
084    
085        private final String xpath;
086        private final XPathEvaluator evaluator;
087    
088        public static interface XPathEvaluator {
089            boolean evaluate(Message message) throws JMSException;
090        }
091    
092        XPathExpression(String xpath) {
093            this.xpath = xpath;
094            this.evaluator = createEvaluator(xpath);
095        }
096    
097        private static Constructor getXPathEvaluatorConstructor(String cn) throws ClassNotFoundException, SecurityException, NoSuchMethodException {
098            Class c = XPathExpression.class.getClassLoader().loadClass(cn);
099            if (!XPathEvaluator.class.isAssignableFrom(c)) {
100                throw new ClassCastException("" + c + " is not an instance of " + XPathEvaluator.class);
101            }
102            return c.getConstructor(new Class[] {String.class, DocumentBuilder.class});
103        }
104    
105        protected static void setupFeatures(DocumentBuilderFactory factory) {
106            Properties properties = System.getProperties();
107            List<String> features = new ArrayList<String>();
108            for (Map.Entry<Object, Object> prop : properties.entrySet()) {
109                String key = (String) prop.getKey();
110                if (key.startsWith(DOCUMENT_BUILDER_FACTORY_FEATURE)) {
111                    String uri = key.split(DOCUMENT_BUILDER_FACTORY_FEATURE + ":")[1];
112                    Boolean value = Boolean.valueOf((String)prop.getValue());
113                    try {
114                        factory.setFeature(uri, value);
115                        features.add("feature " + uri + " value " + value);
116                    } catch (ParserConfigurationException e) {
117                        LOG.warn("DocumentBuilderFactory doesn't support the feature {} with value {}, due to {}.", new Object[]{uri, value, e});
118                    }
119                }
120            }
121            if (features.size() > 0) {
122                StringBuffer featureString = new StringBuffer();
123                // just log the configured feature
124                for (String feature : features) {
125                    if (featureString.length() != 0) {
126                        featureString.append(", ");
127                    }
128                    featureString.append(feature);
129                }
130            }
131    
132        }
133    
134        private XPathEvaluator createEvaluator(String xpath2) {
135            try {
136                return (XPathEvaluator)EVALUATOR_CONSTRUCTOR.newInstance(new Object[] {xpath, builder});
137            } catch (InvocationTargetException e) {
138                Throwable cause = e.getCause();
139                if (cause instanceof RuntimeException) {
140                    throw (RuntimeException)cause;
141                }
142                throw new RuntimeException("Invalid XPath Expression: " + xpath + " reason: " + e.getMessage(), e);
143            } catch (Throwable e) {
144                throw new RuntimeException("Invalid XPath Expression: " + xpath + " reason: " + e.getMessage(), e);
145            }
146        }
147    
148        public Object evaluate(MessageEvaluationContext message) throws JMSException {
149            try {
150                if (message.isDropped()) {
151                    return null;
152                }
153                return evaluator.evaluate(message.getMessage()) ? Boolean.TRUE : Boolean.FALSE;
154            } catch (IOException e) {
155                throw JMSExceptionSupport.create(e);
156            }
157    
158        }
159    
160        public String toString() {
161            return "XPATH " + ConstantExpression.encodeString(xpath);
162        }
163    
164        /**
165         * @param message
166         * @return true if the expression evaluates to Boolean.TRUE.
167         * @throws JMSException
168         */
169        public boolean matches(MessageEvaluationContext message) throws JMSException {
170            Object object = evaluate(message);
171            return object != null && object == Boolean.TRUE;
172        }
173    
174    }