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Java > Open Source Codes > org > apache > commons > jelly > expression > jexl > JexlExpressionFactory


1 /*
2  * Copyright 2002,2004 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16
17 package org.apache.commons.jelly.expression.jexl;
18
19 import org.apache.commons.jelly.JellyContext;
20 import org.apache.commons.jelly.JellyException;
21 import org.apache.commons.jelly.expression.Expression;
22 import org.apache.commons.jelly.expression.ExpressionSupport;
23 import org.apache.commons.jelly.expression.ExpressionFactory;
24
25 //import org.apache.commons.jexl.resolver.FlatResolver;
26
27 /**
28  * Represents a factory of <a HREF="http://jakarta.apache.org/commons/jexl.html">Jexl</a>
29  * expression which fully supports the Expression Language in JSTL and JSP.
30  * In addition this ExpressionFactory can also support Ant style variable
31  * names, where '.' is used inside variable names.
32  *
33  * @author <a HREF="mailto:jstrachan@apache.org">James Strachan</a>
34  * @version $Revision: 155420 $
35  */
36
37 public class JexlExpressionFactory implements ExpressionFactory {
38
39     /** whether we should allow Ant-style expresssions, using dots as part of variable name */
40     private boolean supportAntVariables = true;
41
42     // ExpressionFactory interface
43 //-------------------------------------------------------------------------
44 public Expression createExpression(String JavaDoc text) throws JellyException {
45 /*
46
47         org.apache.commons.jexl.Expression expr =
48             org.apache.commons.jexl.ExpressionFactory.createExpression(text);
49
50         if ( isSupportAntVariables() ) {
51             expr.addPostResolver(new FlatResolver());
52         }
53
54         return new JexlExpression( expr );
55 */
56
57         Expression jexlExpression = null;
58         try {
59             // this method really does throw Exception
60 jexlExpression = new JexlExpression(
61             org.apache.commons.jexl.ExpressionFactory.createExpression(text)
62             );
63         } catch (Exception JavaDoc e) {
64             throw new JellyException("Unable to create expression: " + text, e);
65         }
66
67         if ( isSupportAntVariables() && isValidAntVariableName(text) ) {
68             return new ExpressionSupportLocal(jexlExpression,text);
69         }
70         return jexlExpression;
71     }
72
73     // Properties
74 //-------------------------------------------------------------------------
75
76     /**
77      * @return whether we should allow Ant-style expresssions, using dots as
78      * part of variable name
79      */
80     public boolean isSupportAntVariables() {
81         return supportAntVariables;
82     }
83
84     /**
85      * Sets whether we should allow Ant-style expresssions, using dots as
86      * part of variable name
87      */
88     public void setSupportAntVariables(boolean supportAntVariables) {
89         this.supportAntVariables = supportAntVariables;
90     }
91
92     // Implementation methods
93 //-------------------------------------------------------------------------
94
95     /**
96      * @return true if the given string is a valid Ant variable name,
97      * typically thats alphanumeric text with '.' etc.
98      */
99     protected boolean isValidAntVariableName(String JavaDoc text) {
100         char[] chars = text.toCharArray();
101         for (int i = 0, size = chars.length; i < size; i++ ) {
102             char ch = chars[i];
103             // could maybe be a bit more restrictive...
104 if ( Character.isWhitespace(ch) || ch == '[' || ch == ']' || ch == '(' || ch == ')') {
105                 return false;
106             }
107         }
108         return true;
109     }
110
111     private class ExpressionSupportLocal extends ExpressionSupport {
112
113         protected Expression jexlExpression = null;
114         protected String JavaDoc text = null;
115
116         public ExpressionSupportLocal(Expression jexlExpression, String JavaDoc text) {
117             this.jexlExpression = jexlExpression;
118             this.text = text;
119         }
120
121         public Object JavaDoc evaluate(JellyContext context) {
122             Object JavaDoc answer = jexlExpression.evaluate(context);
123
124             if ( answer == null ) {
125                 answer = context.getVariable(text);
126             }
127
128             return answer;
129         }
130
131         public String JavaDoc getExpressionText() {
132             return "${" + text + "}";
133         }
134
135         public String JavaDoc toString() {
136             return super.toString() + "[expression:" + text + "]";
137         }
138     }
139
140 }
141
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