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 */
017package org.apache.activemq.filter;
018
019import java.io.IOException;
020import java.lang.reflect.Constructor;
021import java.lang.reflect.InvocationTargetException;
022
023import javax.jms.JMSException;
024
025import org.apache.activemq.command.Message;
026import org.apache.activemq.util.JMSExceptionSupport;
027import org.slf4j.Logger;
028import org.slf4j.LoggerFactory;
029
030/**
031 * Used to evaluate an XPath Expression in a JMS selector.
032 */
033public final class XPathExpression implements BooleanExpression {
034
035    private static final Logger LOG = LoggerFactory.getLogger(XPathExpression.class);
036    private static final String EVALUATOR_SYSTEM_PROPERTY = "org.apache.activemq.XPathEvaluatorClassName";
037    private static final String DEFAULT_EVALUATOR_CLASS_NAME = XalanXPathEvaluator.class.getName();
038
039    private static final Constructor EVALUATOR_CONSTRUCTOR;
040
041    static {
042        String cn = System.getProperty(EVALUATOR_SYSTEM_PROPERTY, DEFAULT_EVALUATOR_CLASS_NAME);
043        Constructor m = null;
044        try {
045            try {
046                m = getXPathEvaluatorConstructor(cn);
047            } catch (Throwable e) {
048                LOG.warn("Invalid " + XPathEvaluator.class.getName() + " implementation: " + cn + ", reason: " + e, e);
049                cn = DEFAULT_EVALUATOR_CLASS_NAME;
050                try {
051                    m = getXPathEvaluatorConstructor(cn);
052                } catch (Throwable e2) {
053                    LOG.error("Default XPath evaluator could not be loaded", e);
054                }
055            }
056        } finally {
057            EVALUATOR_CONSTRUCTOR = m;
058        }
059    }
060
061    private final String xpath;
062    private final XPathEvaluator evaluator;
063
064    public static interface XPathEvaluator {
065        boolean evaluate(Message message) throws JMSException;
066    }
067
068    XPathExpression(String xpath) {
069        this.xpath = xpath;
070        this.evaluator = createEvaluator(xpath);
071    }
072
073    private static Constructor getXPathEvaluatorConstructor(String cn) throws ClassNotFoundException, SecurityException, NoSuchMethodException {
074        Class c = XPathExpression.class.getClassLoader().loadClass(cn);
075        if (!XPathEvaluator.class.isAssignableFrom(c)) {
076            throw new ClassCastException("" + c + " is not an instance of " + XPathEvaluator.class);
077        }
078        return c.getConstructor(new Class[] {String.class});
079    }
080
081    private XPathEvaluator createEvaluator(String xpath2) {
082        try {
083            return (XPathEvaluator)EVALUATOR_CONSTRUCTOR.newInstance(new Object[] {xpath});
084        } catch (InvocationTargetException e) {
085            Throwable cause = e.getCause();
086            if (cause instanceof RuntimeException) {
087                throw (RuntimeException)cause;
088            }
089            throw new RuntimeException("Invalid XPath Expression: " + xpath + " reason: " + e.getMessage(), e);
090        } catch (Throwable e) {
091            throw new RuntimeException("Invalid XPath Expression: " + xpath + " reason: " + e.getMessage(), e);
092        }
093    }
094
095    public Object evaluate(MessageEvaluationContext message) throws JMSException {
096        try {
097            if (message.isDropped()) {
098                return null;
099            }
100            return evaluator.evaluate(message.getMessage()) ? Boolean.TRUE : Boolean.FALSE;
101        } catch (IOException e) {
102            throw JMSExceptionSupport.create(e);
103        }
104
105    }
106
107    public String toString() {
108        return "XPATH " + ConstantExpression.encodeString(xpath);
109    }
110
111    /**
112     * @param message
113     * @return true if the expression evaluates to Boolean.TRUE.
114     * @throws JMSException
115     */
116    public boolean matches(MessageEvaluationContext message) throws JMSException {
117        Object object = evaluate(message);
118        return object != null && object == Boolean.TRUE;
119    }
120
121}