ExpressionUtil


1   /*
2    * Copyright 1999-2004 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.taglibs.standard.tag.el.core;
18  
19  import javax.servlet.jsp.JspException  ;
20  import javax.servlet.jsp.PageContext  ;
21  import javax.servlet.jsp.tagext.Tag  ;
22  
23  import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;
24  import org.apache.taglibs.standard.tag.common.core.NullAttributeException;
25  
26  /**
27   * <p>Contains some static utilities to facilitate common forms of
28   * expression evaluation.</p>
29   *
30   * @author Shawn Bayern
31   */
32  
33  public class ExpressionUtil {
34  
35      /** Evaluates an expression if present, but does not allow the expression
36       *  to evaluate to 'null', throwing a NullAttributeException if it
37       *  does.  The function <b>can</b> return null, however, if the
38       *  expression itself is null.
39       */
40      public static Object   evalNotNull(String   tagName,
41                       String   attributeName,
42                                   String   expression,
43                       Class   expectedType,
44                       Tag   tag,
45                                   PageContext   pageContext)
46              throws JspException   {
47          if (expression != null) {
48              Object   r = ExpressionEvaluatorManager.evaluate(
49                  attributeName, expression, expectedType, tag, pageContext);
50              if (r == null)
51                  throw new NullAttributeException(tagName, attributeName);
52          return r;
53          } else
54          return null;
55      }
56  }
57
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