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Java > Open Source Codes > org > apache > taglibs > page > ExistsAttributeTag


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.page;
18
19 import java.util.*;
20 import javax.servlet.*;
21 import javax.servlet.http.*;
22 import javax.servlet.jsp.*;
23 import javax.servlet.jsp.tagext.*;
24
25 /**
26  * JSP Tag <b>existsAttribute</b>, used to determine if a PageContext
27  * attribute exists.
28  * <p>
29  * Includes the body of the tag if the attribute exists.
30  * <p>
31  * You can set the optional tag attribute <b>value</b> to <i>true</i> or
32  * <i>false</i>. The body of the tag is included if existsAttribute matches
33  * the value.
34  * <p>
35  * JSP Tag Lib Descriptor
36  * <p><pre>
37  * &lt;name&gt;existsAttribute&lt;/name&gt;
38  * &lt;tagclass&gt;org.apache.taglibs.page.ExistsAttributeTag&lt;/tagclass&gt;
39  * &lt;bodycontent&gt;JSP&lt;/bodycontent&gt;
40  * &lt;info&gt;Includes the body of the tag if the page attribute exists.&lt;/info&gt;
41  * &lt;attribute&gt;
42  * &lt;name&gt;name&lt;/name&gt;
43  * &lt;required&gt;true&lt;/required&gt;
44  * &lt;rtexprvalue&gt;false&lt;/rtexprvalue&gt;
45  * &lt;/attribute&gt;
46  * &lt;attribute&gt;
47  * &lt;name&gt;value&lt;/name&gt;
48  * &lt;required&gt;false&lt;/required&gt;
49  * &lt;rtexprvalue&gt;false&lt;/rtexprvalue&gt;
50  * &lt;/attribute&gt;
51  * </pre>
52  *
53  * @author Morgan Delagrange
54  */
55
56 public class ExistsAttributeTag extends TagSupport
57 {
58     private String JavaDoc name = null;
59     private boolean value = true;
60
61     /**
62      * Includes the body of the tag if the page attribute exists.
63      *
64      * @return SKIP_BODY if existsAttribute doesn't match value, EVAL_BODY_include if existsAttribute matches value
65      */
66     public final int doStartTag() throws JspException
67     {
68     boolean result = false;
69     if( pageContext.getAttribute(name) != null )
70         result = true;
71
72     if( value == result )
73         return EVAL_BODY_INCLUDE;
74
75     return SKIP_BODY;
76     }
77
78     /**
79      * Set the required tag attribute <b>name</b>.
80      *
81      * @param String name of page attribute
82      */
83     public final void setName(String JavaDoc str)
84     {
85     name = str;
86     }
87
88     /**
89      * Set the optional tag attribute <b>value</b> to true or false.
90      *
91      * @param boolean true or false
92      */
93     public final void setValue(boolean value)
94     {
95     this.value = value;
96     }
97
98 }
99
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