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.geronimo.system.configuration.condition;
018
019 import java.util.HashMap;
020 import java.util.Map;
021 import java.util.Properties;
022
023 import org.apache.commons.jexl.Expression;
024 import org.apache.commons.jexl.ExpressionFactory;
025 import org.apache.commons.jexl.JexlContext;
026 import org.apache.commons.jexl.JexlHelper;
027 import org.apache.commons.jexl.context.HashMapContext;
028 import org.apache.commons.logging.Log;
029 import org.apache.commons.logging.LogFactory;
030
031 /**
032 * Provides a simple facility to evaluate condition expressions using the
033 * <a href="http://jakarta.apache.org/commons/jexl">Jexl</a> language.
034 *
035 * <p>
036 * This class is thread-safe.
037 * </p>
038 *
039 * @version $Rev: 706640 $ $Date: 2008-10-21 14:44:05 +0000 (Tue, 21 Oct 2008) $
040 */
041 public class JexlConditionParser
042 implements ConditionParser
043 {
044 private static final Log log = LogFactory.getLog(JexlConditionParser.class);
045
046 private final Map<String, Object> vars;
047
048 public JexlConditionParser(final Map vars) {
049 if (vars == null) {
050 throw new IllegalArgumentException("vars");
051 }
052 this.vars = vars;
053 }
054
055 public JexlConditionParser() {
056 // Setup the default vars
057 vars = new HashMap<String, Object>();
058 ParserUtils.addDefaultVariables(vars);
059 }
060
061 /**
062 * Evaluate a condition expression.
063 *
064 * @param expression The condition expression to evaluate; must not be null
065 * @return True if the condition is satisfied
066 *
067 * @throws org.apache.geronimo.system.configuration.condition.ConditionParserException Failed to evaluate condition expression
068 */
069 public boolean evaluate(final String expression) throws ConditionParserException {
070 if (expression == null) {
071 throw new IllegalArgumentException("Expression must not be null");
072 }
073
074 // Empty expressions are true
075 if (expression.trim().length() == 0) {
076 log.debug("Expression is empty; skipping evaluation");
077
078 return true;
079 }
080
081 Object result;
082 try {
083 result = doEvaluate(expression);
084 }
085 catch (Exception e) {
086 throw new ConditionParserException("Failed to evaluate expression: " + expression, e);
087 }
088
089 if (result instanceof Boolean) {
090 return (Boolean) result;
091 }
092 else {
093 throw new ConditionParserException("Expression '" + expression + "' did not evaluate to a boolean value; found: " + result);
094 }
095 }
096
097 private Object doEvaluate(final String expression) throws Exception {
098 assert expression != null;
099
100 boolean debug = log.isDebugEnabled();
101
102 if (debug) {
103 log.debug("Evaluating expression: " + expression);
104 }
105
106 Expression expr = ExpressionFactory.createExpression(expression);
107
108 JexlContext ctx = JexlHelper.createContext();
109 ctx.setVars(vars);
110
111 Object result = expr.evaluate(ctx);
112 if (debug) {
113 log.debug("Result: " + result);
114 }
115
116 return result;
117 }
118 }