001 /** 002 * Copyright (c) 2010 Yahoo! Inc. All rights reserved. 003 * Licensed under the Apache License, Version 2.0 (the "License"); 004 * you may not use this file except in compliance with the License. 005 * You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software 010 * distributed under the License is distributed on an "AS IS" BASIS, 011 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 012 * See the License for the specific language governing permissions and 013 * limitations under the License. See accompanying LICENSE file. 014 */ 015 package org.apache.oozie.util; 016 017 import org.apache.commons.el.ExpressionEvaluatorImpl; 018 019 import javax.servlet.jsp.el.ELException; 020 import javax.servlet.jsp.el.ExpressionEvaluator; 021 import javax.servlet.jsp.el.FunctionMapper; 022 import javax.servlet.jsp.el.VariableResolver; 023 import java.lang.reflect.Method; 024 import java.lang.reflect.Modifier; 025 import java.util.HashMap; 026 import java.util.Map; 027 028 /** 029 * JSP Expression Language Evaluator. <p/> It provides a more convenient way of using the JSP EL Evaluator. 030 */ 031 public class ELEvaluator { 032 033 /** 034 * Provides functions and variables for the EL evaluator. <p/> All functions and variables in the context of an EL 035 * evaluator are accessible from EL expressions. 036 */ 037 public static class Context implements VariableResolver, FunctionMapper { 038 private Map<String, Object> vars; 039 private Map<String, Method> functions; 040 041 /** 042 * Create an empty context. 043 */ 044 public Context() { 045 vars = new HashMap<String, Object>(); 046 functions = new HashMap<String, Method>(); 047 } 048 049 /** 050 * Add variables to the context. <p/> 051 * 052 * @param vars variables to add to the context. 053 */ 054 public void setVariables(Map<String, Object> vars) { 055 this.vars.putAll(vars); 056 } 057 058 /** 059 * Add a variable to the context. <p/> 060 * 061 * @param name variable name. 062 * @param value variable value. 063 */ 064 public void setVariable(String name, Object value) { 065 vars.put(name, value); 066 } 067 068 /** 069 * Return a variable from the context. <p/> 070 * 071 * @param name variable name. 072 * @return the variable value. 073 */ 074 public Object getVariable(String name) { 075 return vars.get(name); 076 } 077 078 /** 079 * Add a function to the context. <p/> 080 * 081 * @param prefix function prefix. 082 * @param functionName function name. 083 * @param method method that will be invoked for the function, it must be a static and public method. 084 */ 085 public void addFunction(String prefix, String functionName, Method method) { 086 if ((method.getModifiers() & (Modifier.PUBLIC | Modifier.STATIC)) != (Modifier.PUBLIC | Modifier.STATIC)) { 087 throw new IllegalArgumentException(XLog.format("Method[{0}] must be public and static", method)); 088 } 089 prefix = (prefix.length() > 0) ? prefix + ":" : ""; 090 functions.put(prefix + functionName, method); 091 } 092 093 /** 094 * Resolve a variable name. Used by the EL evaluator implemenation. <p/> 095 * 096 * @param name variable name. 097 * @return the variable value. 098 * @throws ELException thrown if the variable is not defined in the context. 099 */ 100 public Object resolveVariable(String name) throws ELException { 101 if (!vars.containsKey(name)) { 102 throw new ELException(XLog.format("variable [{0}] cannot be resolved", name)); 103 } 104 return vars.get(name); 105 } 106 107 /** 108 * Resolve a function prefix:name. Used by the EL evaluator implementation. <p/> 109 * 110 * @param prefix function prefix. 111 * @param name function name. 112 * @return the method associated to the function. 113 */ 114 public Method resolveFunction(String prefix, String name) { 115 if (prefix.length() > 0) { 116 name = prefix + ":" + name; 117 } 118 return functions.get(name); 119 } 120 } 121 122 private static ThreadLocal<ELEvaluator> current = new ThreadLocal<ELEvaluator>(); 123 124 /** 125 * If within the scope of a EL evaluation call, it gives access to the ELEvaluator instance performing the EL 126 * evaluation. <p/> This is useful for EL function methods to get access to the variables of the Evaluator. Because 127 * of this, ELEvaluator variables can be used to pass context to EL function methods (which must be static methods). 128 * <p/> 129 * 130 * @return the ELEvaluator in scope, or <code>null</code> if none. 131 */ 132 public static ELEvaluator getCurrent() { 133 return current.get(); 134 } 135 136 private Context context; 137 138 private ExpressionEvaluator evaluator = new ExpressionEvaluatorImpl(); 139 140 /** 141 * Creates an ELEvaluator with no functions and no variables defined. 142 */ 143 public ELEvaluator() { 144 this(new Context()); 145 } 146 147 /** 148 * Creates an ELEvaluator with the functions and variables defined in the given {@link ELEvaluator.Context}. <p/> 149 * 150 * @param context the ELSupport with functions and variables to be available for EL evalution. 151 */ 152 public ELEvaluator(Context context) { 153 this.context = context; 154 } 155 156 /** 157 * Return the context with the functions and variables of the EL evaluator. <p/> 158 * 159 * @return the context. 160 */ 161 public Context getContext() { 162 return context; 163 } 164 165 /** 166 * Convenience method that sets a variable in the EL evaluator context. <p/> 167 * 168 * @param name variable name. 169 * @param value variable value. 170 */ 171 public void setVariable(String name, Object value) { 172 context.setVariable(name, value); 173 } 174 175 /** 176 * Convenience method that returns a variable from the EL evaluator context. <p/> 177 * 178 * @param name variable name. 179 * @return the variable value, <code>null</code> if not defined. 180 */ 181 public Object getVariable(String name) { 182 return context.getVariable(name); 183 } 184 185 /** 186 * Evaluate an EL expression. <p/> 187 * 188 * @param expr EL expression to evaluate. 189 * @param clazz return type of the EL expression. 190 * @return the object the EL expression evaluated to. 191 * @throws Exception thrown if an EL function failed due to a transient error or EL expression could not be 192 * evaluated. 193 */ 194 @SuppressWarnings({"unchecked", "deprecation"}) 195 public <T> T evaluate(String expr, Class<T> clazz) throws Exception { 196 ELEvaluator existing = current.get(); 197 try { 198 current.set(this); 199 return (T) evaluator.evaluate(expr, clazz, context, context); 200 } 201 catch (ELException ex) { 202 if (ex.getRootCause() instanceof Exception) { 203 throw (Exception) ex.getRootCause(); 204 } 205 else { 206 throw ex; 207 } 208 } 209 finally { 210 current.set(existing); 211 } 212 } 213 214 }