View Javadoc

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://commons.apache.org/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 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 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 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 text = null;
115 
116         public ExpressionSupportLocal(Expression jexlExpression, String text) {
117             this.jexlExpression = jexlExpression;
118             this.text = text;
119         }
120 
121         public Object evaluate(JellyContext context) {
122             Object answer = jexlExpression.evaluate(context);
123 
124             if ( answer == null ) {
125                 answer = context.getVariable(text);
126             }
127 
128             return answer;
129         }
130 
131         public String getExpressionText() {
132             return "${" + text + "}";
133         }
134 
135         public String toString() {
136             return super.toString() + "[expression:" + text + "]";
137         }
138     }
139 
140 }