EvalHelper


1   /*
2    * $Id: EvalHelper.java 54933 2004-10-16 17:04:52Z germuska $ 
3    *
4    * Copyright 1999-2004 The Apache Software Foundation.
5    * 
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    * 
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   * 
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.strutsel.taglib.utils;
20  
21  import javax.servlet.jsp.PageContext  ;
22  import javax.servlet.jsp.JspException  ;
23  import javax.servlet.jsp.tagext.Tag  ;
24  import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;
25  
26  /**
27   * This class is used in the <code>evaluateExpressions</code> method of each
28   * Tag class.  It is used to process the original attribute value through the
29   * JSTL EL engine to produce an evaluated value.  It provides functions to
30   * evaluate the expression assuming it is an Object, String, Integer, or
31   * Boolean result.
32   */
33  public final class EvalHelper
34  {
35      private EvalHelper() {}
36  
37      /**
38       * Evaluates the attribute value in the JSTL EL engine, returning the raw
39       * Object value of the evaluated expression.  If the original expression is
40       * null, or the resulting value is null, it will return null.
41       */
42      public static Object   eval(String        attrName,
43                                String        attrValue,
44                                Tag           tagObject,
45                                PageContext   pageContext) 
46          throws JspException  
47      {
48          Object   result   = null;
49          if (attrValue != null) {
50              result   =
51                  ExpressionEvaluatorManager.
52                  evaluate(attrName, attrValue, Object  .class, tagObject,
53                           pageContext);
54          }
55  
56          return (result);
57      }
58  
59      /**
60       * Evaluates the attribute value in the JSTL EL engine, assuming the
61       * resulting value is a String object.  If the original expression is null,
62       * or the resulting value is null, it will return null.
63       */
64      public static String   evalString(String        attrName,
65                                      String        attrValue,
66                                      Tag           tagObject,
67                                      PageContext   pageContext) 
68          throws JspException  
69      {
70          Object   result   = null;
71          if (attrValue != null) {
72              result   =
73                  ExpressionEvaluatorManager.
74                  evaluate(attrName, attrValue, String  .class, tagObject,
75                           pageContext);
76          }
77  
78          return ((String  ) result);
79      }
80  
81      /**
82       * Evaluates the attribute value in the JSTL EL engine, assuming the
83       * resulting value is an Integer object.  If the original expression is
84       * null, or the resulting value is null, it will return null.
85       */
86      public static Integer   evalInteger(String         attrName,
87                                        String         attrValue,
88                                        Tag            tagObject,
89                                        PageContext    pageContext) 
90          throws JspException  
91      {
92          Object   result   = null;
93          if (attrValue != null) {
94              result   = ExpressionEvaluatorManager.
95                  evaluate(attrName, attrValue, Integer  .class, tagObject,
96                           pageContext);
97          }
98  
99          return ((Integer  ) result);
100     }
101 
102     /**
103      * Evaluates the attribute value in the JSTL EL engine, assuming the
104      * resulting value is an Boolean object.  If the original expression is
105      * null, or the resulting value is null, it will return null.
106      */
107     public static Boolean   evalBoolean(String         attrName,
108                                       String         attrValue,
109                                       Tag            tagObject,
110                                       PageContext    pageContext) 
111         throws JspException  
112     {
113         Object   result   = null;
114         if (attrValue != null) {
115             result   = ExpressionEvaluatorManager.
116                 evaluate(attrName, attrValue, Boolean  .class, tagObject,
117                          pageContext);
118         }
119 
120         return ((Boolean  ) result);
121     }
122 }
123
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