ELBaseTag


1   /*
2    * $Id: ELBaseTag.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.html;
20  
21  import org.apache.struts.taglib.html.BaseTag;
22  import javax.servlet.jsp.JspException  ;
23  import org.apache.strutsel.taglib.utils.EvalHelper;
24  
25  /**
26   * Renders an HTML <base> element with an href 
27   * attribute pointing to the absolute location of the enclosing JSP page. This 
28   * tag is only valid when nested inside a head tag body. The presence 
29   * of this tag allows the browser to resolve relative URL's to images,
30   * CSS stylesheets  and other resources in a manner independent of the URL
31   * used to call the ActionServlet.
32   *<p>
33   * This class is a subclass of the class
34   * <code>org.apache.struts.taglib.html.BaseTag</code> which provides most of
35   * the described functionality.  This subclass allows all attribute values to
36   * be specified as expressions utilizing the JavaServer Pages Standard Library
37   * expression language.
38   *
39   * @version $Rev: 54933 $
40   */
41  public class ELBaseTag extends BaseTag {
42  
43      /**
44       * Instance variable mapped to "target" tag attribute.
45       * (Mapping set in associated BeanInfo class.)
46       */
47      private String   targetExpr;
48      /**
49       * Instance variable mapped to "server" tag attribute.
50       * (Mapping set in associated BeanInfo class.)
51       */
52      private String   serverExpr;
53  
54      /**
55       * Getter method for "target" tag attribute.
56       * (Mapping set in associated BeanInfo class.)
57       */
58      public String   getTargetExpr() { return (targetExpr); }
59      /**
60       * Getter method for "server" tag attribute.
61       * (Mapping set in associated BeanInfo class.)
62       */
63      public String   getServerExpr() { return (serverExpr); }
64  
65      /**
66       * Setter method for "target" tag attribute.
67       * (Mapping set in associated BeanInfo class.)
68       */
69      public void setTargetExpr(String   targetExpr) { this.targetExpr = targetExpr; }
70      /**
71       * Setter method for "server" tag attribute.
72       * (Mapping set in associated BeanInfo class.)
73       */
74      public void setServerExpr(String   serverExpr) { this.serverExpr = serverExpr; }
75  
76      /**
77       * Resets attribute values for tag reuse.
78       */
79      public void release()
80      {
81          super.release();
82          setTargetExpr(null);
83          setServerExpr(null);
84      }
85      
86      /**
87       * Process the start tag.
88       *
89       * @exception JspException if a JSP exception has occurred
90       */
91      public int doStartTag() throws JspException   {
92          evaluateExpressions();
93          return (super.doStartTag());
94      }
95  
96      /**
97       * Processes all attribute values which use the JSTL expression evaluation
98       * engine to determine their values.
99       *
100      * @exception JspException if a JSP exception has occurred
101      */
102     private void evaluateExpressions() throws JspException   {
103         String    string  = null;
104 
105         if ((string = EvalHelper.evalString("target", getTargetExpr(),
106                                             this, pageContext)) != null)
107             setTarget(string);
108 
109         if ((string = EvalHelper.evalString("server", getServerExpr(),
110                                             this, pageContext)) != null)
111             setServer(string);
112     }
113 }
114
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