ExprTag


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.xml;
18  
19  import javax.servlet.jsp.JspException  ;
20  
21  import org.apache.taglibs.standard.tag.common.xml.ExprSupport;
22  import org.apache.taglibs.standard.tag.el.core.ExpressionUtil;
23  
24  /**
25   * <p>A handler for &lt;out&gt; that accepts attributes as Strings
26   * and evaluates them as expressions at runtime.</p>
27   *
28   * @author Shawn Bayern
29   */
30  public class ExprTag extends ExprSupport {
31  
32      //*********************************************************************
33      // 'Private' state (implementation details)
34  
35      private String   escapeXml_;                  // stores EL-based property
36  
37  
38      //*********************************************************************
39      // Constructor
40  
41      /**
42       * Constructs a new handler.  As with TagSupport, subclasses
43       * should not provide other constructors and are expected to call
44       * the superclass constructor
45       */
46      public ExprTag() {
47          super();
48          init();
49      }
50  
51  
52      //*********************************************************************
53      // Tag logic
54  
55      // evaluates expression and chains to parent
56      public int doStartTag() throws JspException   {
57  
58          // evaluate any expressions we were passed, once per invocation
59          evaluateExpressions();
60  
61      // chain to the parent implementation
62      return super.doStartTag();
63      }
64  
65  
66      // Releases any resources we may have (or inherit)
67      public void release() {
68          super.release();
69          init();
70      }
71  
72  
73      //*********************************************************************
74      // Accessor methods
75  
76      // for EL-based attribute
77      public void setEscapeXml(String   escapeXml_) {
78          this.escapeXml_ = escapeXml_;
79      }
80  
81  
82      //*********************************************************************
83      // Private (utility) methods
84  
85      // (re)initializes state (during release() or construction)
86      private void init() {
87          // null implies "no expression"
88      escapeXml_ = null;
89      }
90  
91      /* Evaluates expressions as necessary */
92      private void evaluateExpressions() throws JspException   {
93          /* 
94           * Note: we don't check for type mismatches here; we assume
95           * the expression evaluator will return the expected type
96           * (by virtue of knowledge we give it about what that type is).
97           * A ClassCastException here is truly unexpected, so we let it
98           * propagate up.
99           */
100 
101         if (escapeXml_ != null) {
102             Boolean   b = (Boolean  ) ExpressionUtil.evalNotNull(
103                 "out",
104                 "escapeXml",
105                 escapeXml_,
106                 Boolean  .class,
107                 this,
108                 pageContext);
109             if (b == null)
110                 escapeXml = false;
111             else
112                 escapeXml = b.booleanValue();
113         }
114     }
115 }
116
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