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Java > Open Source Codes > org > apache > commons > jexl > ExpressionImpl


1 /*
2  * Copyright 2002-2006 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.jexl;
18
19 import java.util.ArrayList JavaDoc;
20 import java.util.List JavaDoc;
21
22 import org.apache.commons.jexl.parser.SimpleNode;
23
24 /**
25  * Instances of ExpressionImpl are created by the {@link ExpressionFactory},
26  * and this is the default implementation of the {@link Expression} interface.
27  *
28  * @since 1.0
29  * @author <a HREF="mailto:geirm@apache.org">Geir Magnusson Jr.</a>
30  * @version $Id: ExpressionImpl.java 397111 2006-04-26 06:47:52Z dion $
31  */
32 class ExpressionImpl implements Expression {
33
34     /** resolvers called before expression evaluation. */
35     protected List JavaDoc preResolvers;
36
37     /** resolvers called after expression evaluation. */
38     protected List JavaDoc postResolvers;
39
40     /**
41      * Original expression. This is just a 'snippet', not a valid statement
42      * (i.e. foo.bar() vs foo.bar();
43      */
44     protected String JavaDoc expression;
45
46     /**
47      * The resulting AST we can call value() on.
48      */
49     protected SimpleNode node;
50
51     /**
52      * do not let this be generally instantiated with a 'new'.
53      *
54      * @param expr the expression.
55      * @param ref the parsed expression.
56      */
57     ExpressionImpl(String JavaDoc expr, SimpleNode ref) {
58         expression = expr;
59         node = ref;
60     }
61
62     /**
63      * {@inheritDoc}
64      */
65     public Object JavaDoc evaluate(JexlContext context) throws Exception JavaDoc {
66         Object JavaDoc val = null;
67
68         /*
69          * if we have pre resolvers, give them a wack
70          */
71         if (preResolvers != null) {
72             val = tryResolver(preResolvers, context);
73
74             if (val != JexlExprResolver.NO_VALUE) {
75                 return val;
76             }
77         }
78
79         val = node.value(context);
80
81         /*
82          * if null, call post resolvers
83          */
84         if (val == null && postResolvers != null) {
85             val = tryResolver(postResolvers, context);
86
87             if (val != JexlExprResolver.NO_VALUE) {
88                 return val;
89             }
90         }
91
92         return val;
93     }
94
95     /**
96      * Tries the resolvers in the given resolverlist against the context.
97      *
98      * @param resolverList list of JexlExprResolvers
99      * @param context JexlContext to use for evauluation
100      * @return value (including null) or JexlExprResolver.NO_VALUE
101      */
102     protected Object JavaDoc tryResolver(List JavaDoc resolverList, JexlContext context) {
103         Object JavaDoc val = JexlExprResolver.NO_VALUE;
104         String JavaDoc expr = getExpression();
105
106         for (int i = 0; i < resolverList.size(); i++) {
107             JexlExprResolver jer = (JexlExprResolver) resolverList.get(i);
108
109             val = jer.evaluate(context, expr);
110
111             /*
112              * as long as it's not NO_VALUE, return it
113              */
114             if (val != JexlExprResolver.NO_VALUE) {
115                 return val;
116             }
117         }
118
119         return val;
120     }
121
122     /**
123      * {@inheritDoc}
124      */
125     public String JavaDoc getExpression() {
126         return expression;
127     }
128
129     /**
130      * {@inheritDoc}
131      */
132     public void addPreResolver(JexlExprResolver resolver) {
133         if (preResolvers == null) {
134             preResolvers = new ArrayList JavaDoc();
135         }
136         preResolvers.add(resolver);
137     }
138
139     /**
140      * {@inheritDoc}
141      */
142     public void addPostResolver(JexlExprResolver resolver) {
143         if (postResolvers == null) {
144             postResolvers = new ArrayList JavaDoc();
145         }
146         postResolvers.add(resolver);
147     }
148
149     /**
150      * Provide a string representation of the expression.
151      *
152      * @return the expression or blank if it's null.
153      */
154     public String JavaDoc toString() {
155         String JavaDoc expr = getExpression();
156         return expr == null ? "" : expr;
157     }
158
159 }
160
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