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.logging.Log; 028 import org.apache.commons.logging.LogFactory; 029 030 /** 031 * Provides a simple facility to evaluate condition expressions using the 032 * <a href="http://jakarta.apache.org/commons/jexl">Jexl</a> language. 033 * 034 * <p> 035 * This class is thread-safe. 036 * </p> 037 * 038 * @version $Rev: 514355 $ $Date: 2007-03-03 23:29:59 -0500 (Sat, 03 Mar 2007) $ 039 */ 040 public class JexlConditionParser 041 implements ConditionParser 042 { 043 private static final Log log = LogFactory.getLog(JexlConditionParser.class); 044 045 private final Map<String, Object> vars; 046 047 public JexlConditionParser() { 048 // Setup the default vars 049 vars = new HashMap<String, Object>(); 050 051 vars.put("java", new JavaVariable()); 052 vars.put("os", new OsVariable()); 053 054 // Install properties (to allow getProperty(x,y) to be used for defaults 055 Properties props = new Properties(); 056 props.putAll(System.getProperties()); 057 vars.put("props", props); 058 } 059 060 /** 061 * Evaluate a condition expression. 062 * 063 * @param expression The condition expression to evaluate; must not be null 064 * @return True if the condition is satisfied 065 * 066 * @throws org.apache.geronimo.system.configuration.condition.ConditionParserException Failed to evaluate condition expression 067 */ 068 public boolean evaluate(final String expression) throws ConditionParserException { 069 if (expression == null) { 070 throw new IllegalArgumentException("Expression must not be null"); 071 } 072 073 // Empty expressions are true 074 if (expression.trim().length() == 0) { 075 log.debug("Expression is empty; skipping evaluation"); 076 077 return true; 078 } 079 080 Object result; 081 try { 082 result = doEvaluate(expression); 083 } 084 catch (Exception e) { 085 throw new ConditionParserException("Failed to evaluate expression: " + expression, e); 086 } 087 088 if (result instanceof Boolean) { 089 return (Boolean) result; 090 } 091 else { 092 throw new ConditionParserException("Expression '" + expression + "' did not evaluate to a boolean value; found: " + result); 093 } 094 } 095 096 private Object doEvaluate(final String expression) throws Exception { 097 assert expression != null; 098 099 boolean debug = log.isDebugEnabled(); 100 101 if (debug) { 102 log.debug("Evaluating expression: " + expression); 103 } 104 105 Expression expr = ExpressionFactory.createExpression(expression); 106 107 JexlContext ctx = JexlHelper.createContext(); 108 ctx.setVars(vars); 109 110 Object result = expr.evaluate(ctx); 111 if (debug) { 112 log.debug("Result: " + result); 113 } 114 115 return result; 116 } 117 }