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
018 package org.apache.geronimo.system.configuration.condition;
019
020 import java.util.HashMap;
021 import java.util.Map;
022 import java.util.Properties;
023
024 import ognl.Ognl;
025 import ognl.OgnlContext;
026 import org.apache.commons.logging.Log;
027 import org.apache.commons.logging.LogFactory;
028
029 /**
030 * Provides a simple facility to evaluate condition expressions using the
031 * <a href="http://ognl.org">OGNL</a> language.
032 *
033 * <p>
034 * This class is thread-safe.
035 * </p>
036 *
037 * @version $Rev: 514355 $ $Date: 2007-03-03 23:29:59 -0500 (Sat, 03 Mar 2007) $
038 */
039 public class OgnlConditionParser
040 implements ConditionParser
041 {
042 private static final Log log = LogFactory.getLog(OgnlConditionParser.class);
043
044 private final Map<String, Object> vars;
045
046 public OgnlConditionParser() {
047 // Setup the default vars
048 vars = new HashMap<String, Object>();
049
050 vars.put("java", new JavaVariable());
051 vars.put("os", new OsVariable());
052
053 // Install properties (to allow getProperty(x,y) to be used for defaults
054 Properties props = new Properties();
055 props.putAll(System.getProperties());
056 vars.put("props", props);
057 }
058
059 /**
060 * Evaluate a condition expression.
061 *
062 * @param expression The condition expression to evaluate; must not be null
063 * @return True if the condition is satisfied
064 *
065 * @throws ConditionParserException Failed to evaluate condition expression
066 */
067 public boolean evaluate(final String expression) throws ConditionParserException {
068 if (expression == null) {
069 throw new IllegalArgumentException("Expression must not be null");
070 }
071
072 // Empty expressions are true
073 if (expression.trim().length() == 0) {
074 log.debug("Expression is empty; skipping evaluation");
075
076 return true;
077 }
078
079 Object result;
080 try {
081 result = doEvaluate(expression);
082 }
083 catch (Exception e) {
084 throw new ConditionParserException("Failed to evaluate expression: " + expression, e);
085 }
086
087 if (result instanceof Boolean) {
088 return (Boolean) result;
089 }
090 else {
091 throw new ConditionParserException("Expression '" + expression + "' did not evaluate to a boolean value; found: " + result);
092 }
093 }
094
095 private Object doEvaluate(final String expression) throws Exception {
096 assert expression != null;
097
098 boolean debug = log.isDebugEnabled();
099
100 if (debug) {
101 log.debug("Evaluating expression: " + expression);
102 }
103
104 // Object root;
105 OgnlContext context = new OgnlContext(vars);
106
107 Object expr = Ognl.parseExpression(expression);
108 Object result = Ognl.getValue(expr, context);
109
110 if (debug) {
111 log.debug("Result: " + result);
112 }
113
114 return result;
115 }
116 }