ParamTag


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