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org.apache.commons.jexl.ExpressionFactory |
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1 | /* |
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2 | * Copyright 2002-2006 The Apache Software Foundation. |
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3 | * |
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4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
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5 | * you may not use this file except in compliance with the License. |
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6 | * You may obtain a copy of the License at |
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7 | * |
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8 | * http://www.apache.org/licenses/LICENSE-2.0 |
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9 | * |
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10 | * Unless required by applicable law or agreed to in writing, software |
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11 | * distributed under the License is distributed on an "AS IS" BASIS, |
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12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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13 | * See the License for the specific language governing permissions and |
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14 | * limitations under the License. |
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15 | */ |
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16 | package org.apache.commons.jexl; |
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17 | ||
18 | import java.io.StringReader; |
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19 | ||
20 | import org.apache.commons.jexl.parser.ASTExpressionExpression; |
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21 | import org.apache.commons.jexl.parser.ASTForeachStatement; |
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22 | import org.apache.commons.jexl.parser.ASTIfStatement; |
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23 | import org.apache.commons.jexl.parser.ASTReferenceExpression; |
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24 | import org.apache.commons.jexl.parser.ASTStatementExpression; |
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25 | import org.apache.commons.jexl.parser.ASTWhileStatement; |
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26 | import org.apache.commons.jexl.parser.ParseException; |
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27 | import org.apache.commons.jexl.parser.Parser; |
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28 | import org.apache.commons.jexl.parser.SimpleNode; |
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29 | import org.apache.commons.jexl.parser.TokenMgrError; |
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30 | import org.apache.commons.logging.Log; |
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31 | import org.apache.commons.logging.LogFactory; |
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32 | ||
33 | /** |
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34 | * <p> |
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35 | * Creates Expression objects. To create a JEXL Expression object, pass |
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36 | * valid JEXL syntax to the static createExpression() method: |
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37 | * </p> |
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38 | * |
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39 | * <pre> |
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40 | * String jexl = "array[1]"; |
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41 | * Expression expression = ExpressionFactory.createExpression( jexl ); |
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42 | * </pre> |
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43 | * |
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44 | * <p> |
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45 | * When an {@link Expression} object is created, the JEXL syntax is |
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46 | * parsed and verified. If the supplied expression is neither an |
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47 | * expression nor a reference, an exception is thrown from createException(). |
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48 | * </p> |
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49 | * @since 1.0 |
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50 | * @author <a href="mailto:geirm@apache.org">Geir Magnusson Jr.</a> |
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51 | * @version $Id: ExpressionFactory.java 429169 2006-08-06 18:36:29Z rahul $ |
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52 | */ |
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53 | public class ExpressionFactory { |
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54 | /** |
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55 | * The Log to which all ExpressionFactory messages will be logged. |
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56 | */ |
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57 | 16 | protected static Log log = |
58 | LogFactory.getLog("org.apache.commons.jexl.ExpressionFactory"); |
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59 | ||
60 | /** |
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61 | * The singleton ExpressionFactory also holds a single instance of |
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62 | * {@link Parser}. |
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63 | * When parsing expressions, ExpressionFactory synchronizes on Parser. |
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64 | */ |
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65 | 8 | protected static Parser parser = |
66 | new Parser(class="keyword">new StringReader(";")); //$NON-NLS-1$ |
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67 | ||
68 | /** |
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69 | * ExpressionFactory is a singleton and this is the private |
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70 | * instance fufilling that pattern. |
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71 | */ |
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72 | 8 | protected static ExpressionFactory ef = new ExpressionFactory(); |
73 | ||
74 | /** |
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75 | * Private constructor, the single instance is always obtained |
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76 | * with a call to getInstance(). |
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77 | */ |
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78 | 8 | private ExpressionFactory() { |
79 | 8 | } |
80 | ||
81 | /** |
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82 | * Returns the single instance of ExpressionFactory. |
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83 | * @return the instance of ExpressionFactory. |
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84 | */ |
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85 | protected static ExpressionFactory getInstance() { |
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86 | 274 | return ef; |
87 | } |
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88 | ||
89 | /** |
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90 | * Creates an Expression from a String containing valid |
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91 | * JEXL syntax. This method parses the expression which |
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92 | * must contain either a reference or an expression. |
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93 | * @param expression A String containing valid JEXL syntax |
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94 | * @return An Expression object which can be evaluated with a JexlContext |
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95 | * @throws Exception An exception can be thrown if there is a problem |
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96 | * parsing this expression, or if the expression is neither an |
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97 | * expression or a reference. |
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98 | */ |
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99 | public static Expression createExpression(String expression) |
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100 | throws Exception { |
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101 | 274 | return getInstance().createNewExpression(expression); |
102 | } |
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103 | ||
104 | ||
105 | /** |
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106 | * Creates a new Expression based on the expression string. |
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107 | * |
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108 | * @param expression valid Jexl expression |
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109 | * @return Expression |
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110 | * @throws Exception for a variety of reasons - mostly malformed |
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111 | * Jexl expression |
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112 | */ |
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113 | protected Expression createNewExpression(final String expression) |
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114 | throws Exception { |
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115 | ||
116 | 274 | String expr = cleanExpression(expression); |
117 | ||
118 | // Parse the Expression |
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119 | SimpleNode tree; |
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120 | 274 | synchronized (parser) { |
121 | 274 | log.debug("Parsing expression: " + expr); |
122 | try { |
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123 | 274 | tree = parser.parse(new StringReader(expr)); |
124 | 271 | } catch (TokenMgrError tme) { |
125 | 1 | throw new ParseException(tme.getMessage()); |
126 | } |
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127 | 271 | } |
128 | ||
129 | 271 | if (tree.jjtGetNumChildren() > 1 && log.isWarnEnabled()) { |
130 | 0 | log.warn("The JEXL Expression created will be a reference" |
131 | + " to the first expression from the supplied script: \"" |
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132 | + expression + "\" "); |
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133 | } |
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134 | ||
135 | // Must be a simple reference, expression, statement or if, otherwise |
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136 | // throw an exception. |
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137 | 271 | SimpleNode node = (SimpleNode) tree.jjtGetChild(0); |
138 | ||
139 | // TODO: Can we get rid of these checks? |
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140 | 271 | if (node instanceof ASTReferenceExpression |
141 | || node instanceof ASTExpressionExpression |
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142 | || node instanceof ASTStatementExpression |
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143 | || node instanceof ASTIfStatement |
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144 | || node instanceof ASTWhileStatement |
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145 | || node instanceof ASTForeachStatement |
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146 | ) { |
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147 | 271 | return new ExpressionImpl(expression, node); |
148 | } |
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149 | 0 | log.error("Invalid Expression, node of type: " |
150 | + node.getClass().getName()); |
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151 | 0 | throw new Exception("Invalid Expression: not a Reference, Expression, " |
152 | + "Statement or If"); |
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153 | } |
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154 | ||
155 | /** |
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156 | * Trims the expression and adds a semi-colon if missing. |
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157 | * @param expression to clean |
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158 | * @return trimmed expression ending in a semi-colon |
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159 | */ |
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160 | private String cleanExpression(String expression) { |
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161 | 274 | String expr = expression.trim(); |
162 | 274 | if (!expr.endsWith(";")) { |
163 | 267 | expr += ";"; |
164 | } |
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165 | 274 | return expr; |
166 | } |
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167 | } |
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