AbstractTag


1   /* ===============================================================================
2   *
3   * Part of the InfoGlue Content Management Platform (www.infoglue.org)
4   *
5   * ===============================================================================
6   *
7   *  Copyright (C)
8   *
9   * This program is free software; you can redistribute it and/or modify it under
10  * the terms of the GNU General Public License version 2, as published by the
11  * Free Software Foundation. See the file LICENSE.html for more information.
12  *
13  * This program is distributed in the hope that it will be useful, but WITHOUT
14  * ANY WARRANTY, including the implied warranty of MERCHANTABILITY or FITNESS
15  * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License along with
18  * this program; if not, write to the Free Software Foundation, Inc. / 59 Temple
19  * Place, Suite 330 / Boston, MA 02111-1307 / USA.
20  *
21  * ===============================================================================
22  */
23  package org.infoglue.deliver.taglib;
24  
25  import java.io.IOException  ;
26  import java.util.Collection  ;
27  import java.util.List  ;
28  
29  import javax.servlet.jsp.JspException  ;
30  import javax.servlet.jsp.JspTagException  ;
31  import javax.servlet.jsp.tagext.TagSupport  ;
32  
33  import org.apache.taglibs.standard.tag.el.core.ExpressionUtil;
34  
35  /**
36   * Base class for all tags in the infoglue platform.
37   */
38  public abstract class AbstractTag extends TagSupport   
39  {
40      /**
41       * TODO: remove, use var instead.
42       * 
43       * Indicates (if present) the name of the page context variable to store the result in. 
44       */
45      private String   id;
46      
47      /**
48       * Default constructor.
49       */
50      protected AbstractTag()
51      {
52          super();
53      }
54  
55      /**
56       * TODO: remove, use var instead.
57       * 
58       * Sets the name of the page context variable to store the result in.
59       * 
60       * @param id the id to use.
61       */
62      public void setId(String   id)
63      {
64          this.id = id;
65      }
66  
67      /**
68       * Stores the <code>value</code> in the page context variable indicated by the <code>id</code> attribute.
69       * If the <code>value</code> is null; the page context variable is removed instead.
70       * 
71       * @param value the value to store.
72       */
73      protected void setResultAttribute(Object   value)
74      {
75          if(value == null)
76          {
77              pageContext.removeAttribute(id);
78          }
79          else
80          {
81              pageContext.setAttribute(id, value);
82          }
83      }
84      
85      /**
86       * Depending on wheter the <code>id</code> attribute is set, does one of the following:
87       * 
88       * - stores the value in a page context variable (if the <code>id</code> attribute is set).
89       * - writes the value to the output stream.
90       * 
91       * @param value the value.
92       * @throws JspTagException if an exception occurs when storing/writing the value.
93       */
94      protected void produceResult(Object   value) throws JspTagException  
95      {
96          if(id == null)
97          {
98              write((value == null) ? "" : value.toString());
99          }
100         else
101         {
102             setResultAttribute(value);
103         }
104     }
105 
106     /**
107      * Writes the specified text to the response stream.
108      * 
109      * @param text the text to write.
110      * @throws JspException if an I/O error occurs.
111      */
112     protected void write(final String   text) throws JspTagException  
113     {
114         try 
115         {
116             pageContext.getOut().write(text);
117         }
118         catch(IOException   e)
119         {
120             e.printStackTrace();
121             throw new JspTagException  ("IO error: " + e.getMessage());
122         }
123     }
124 
125     /**
126      * Evaluates an expression if present, but does not allow the expression to evaluate to <code>null</null>.
127      * 
128      * @param tagName the name of the tag.
129      * @param attributeName the name of the attribute to evaluate.
130      * @param expression the expression to evaluate.
131      * @param expectedType the expected type of the evaluated expression.
132      * @return the evaluated expression.
133      * @throws JspException if an error occurs while evaluating the expression.
134      */
135     protected Object   evaluate(String   tagName, String   attributeName, String   expression, Class   expectedType) throws JspException  
136     {
137         return ExpressionUtil.evalNotNull(tagName, attributeName, expression, expectedType, this, pageContext);
138     }
139 
140     /**
141      * Evaluates the expression which must evaluate to an Integer.
142      * 
143      * @param tagName the name of the tag.
144      * @param attributeName the name of the attribute to evaluate.
145      * @param expression the expression to evaluate.
146      * @return the evaluated expression.
147      * @throws JspException if an error occurs while evaluating the expression.
148      */
149     protected Integer   evaluateInteger(String   tagName, String   attributeName, String   expression) throws JspException  
150     {
151         return (Integer  ) evaluate(tagName, attributeName, expression, Integer  .class);
152     }
153 
154     /**
155      * Evaluates the expression which must evaluate to a String.
156      * 
157      * @param tagName the name of the tag.
158      * @param attributeName the name of the attribute to evaluate.
159      * @param expression the expression to evaluate.
160      * @return the evaluated expression.
161      * @throws JspException if an error occurs while evaluating the expression.
162      */
163     protected String   evaluateString(String   tagName, String   attributeName, String   expression) throws JspException  
164     {
165         return (String  ) evaluate(tagName, attributeName, expression, String  .class);
166     }
167 
168     /**
169      * Evaluates the expression which must evaluate to a Collection.
170      * 
171      * @param tagName the name of the tag.
172      * @param attributeName the name of the attribute to evaluate.
173      * @param expression the expression to evaluate.
174      * @return the evaluated expression.
175      * @throws JspException if an error occurs while evaluating the expression.
176      */
177     protected Collection   evaluateCollection(String   tagName, String   attributeName, String   expression) throws JspException  
178     {
179         return (Collection  ) evaluate(tagName, attributeName, expression, Collection  .class);
180     }
181 
182     /**
183      * Evaluates the expression which must evaluate to a List.
184      * 
185      * @param tagName the name of the tag.
186      * @param attributeName the name of the attribute to evaluate.
187      * @param expression the expression to evaluate.
188      * @return the evaluated expression.
189      * @throws JspException if an error occurs while evaluating the expression.
190      */
191     protected List   evaluateList(String   tagName, String   attributeName, String   expression) throws JspException  
192     {
193         return (List  ) evaluate(tagName, attributeName, expression, List  .class);
194     }
195 }
196
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