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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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