JoSQLJSPQueryTag


1   /*
2    * Copyright 2004-2005 Gary Bentley 
3    * 
4    * Licensed under the Apache License, Version 2.0 (the "License"); you may 
5    * not use this file except in compliance with the License. 
6    * You may obtain a copy of the License at 
7    *    http://www.apache.org/licenses/LICENSE-2.0 
8    *
9    * Unless required by applicable law or agreed to in writing, software 
10   * distributed under the License is distributed on an "AS IS" BASIS, 
11   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
12   * See the License for the specific language governing permissions and 
13   * limitations under the License.
14   */
15  package org.josql.contrib;
16  
17  import java.util.List  ;
18  
19  import javax.servlet.jsp.tagext.BodyTagSupport  ;
20  import javax.servlet.jsp.tagext.Tag  ;
21  
22  import javax.servlet.jsp.JspException  ;
23  
24  import org.josql.Query;
25  import org.josql.QueryResults;
26  
27  /**
28   * Allows a JoSQL Query to be used in a JSP.
29   * <p>
30   * Example:
31   * <pre>
32   *   &lt;%@ page import="java.util.Arrays" %>
33   *   &lt;%@ page import="java.io.File" %>
34   *
35   *   &lt;%@ tablib prefix="josql" uri="josqltaglib" %>
36   *
37   *   &lt;josql:query inputList='&lt;%= Arrays.asList (new File ("/home/me/").listFiles ()) %>'
38   *                results="queryResults">
39   *     SELECT *
40   *     FROM   java.io.File
41   *     WHERE  name = '.bashrc'
42   *   &lt;/josql:query>
43   * </pre>
44   * <p>
45   * The body of the tag is taken as the statement to execute.
46   * <p>
47   * Note: this class deliberately does NOT extend {@link Query} since doing so would then
48   * prevent the query from being released via the {@link #release()} method.
49   * <p>
50   * The following <b>attributes</b> are supported:
51   * <ul>
52   *   <li><b>inputList</b> - specifies the name of an attribute that holds the List of objects
53   *       to execute the JoSQL statement against, or is the List of objects.  The attribute
54   *       allows request-time expressions to be used, i.e. the "rtexprvalue" in the .tld file
55   *       is set to <code>true</code>.</li>
56   *   <li><b>results</b> - specifies the name of the attribute to hold the results (instance of:
57   *       {@link QueryResults}).</li>
58   * </ul>
59   */
60  public class JoSQLJSPQueryTag extends BodyTagSupport  
61  {
62  
63      private Object   inputList = null;
64      private String   results = null;
65      private Query query = null;
66  
67      /**
68       * Set the name of the attribute that should hold the results.
69       *
70       * @param r The name.
71       */
72      public void setResults (String   r)
73      {
74  
75      this.results = r;
76  
77      }
78  
79      /**
80       * Set the input list, i.e. the list of objects to execute the JoSQL
81       * statement against.  Can be either a "java.lang.String" which will
82       * indicate the name of an attribute to use, or a "java.util.List"
83       * which will be the list of objects of use.
84       * The list of objects is not gained until the {@link #doEndTag()} method
85       * is called.
86       *
87       * @param l The name or list of objects to execute the statement against.
88       */
89      public void setInputList (Object   l)
90      {
91  
92      this.inputList = l;
93  
94      }
95  
96      /**
97       * When called will parse the tag body into a JoSQL statement.
98       * 
99       * @return {@link Tag#SKIP_BODY} is returned.
100      * @throws JspException If the tag body cannot be parsed into a JoSQL statement.
101      */
102     public int doAfterBody ()
103                         throws JspException  
104     {
105 
106     this.query = new Query ();
107 
108     String   st = this.getBodyContent ().getString ();
109 
110     try
111     {
112 
113         this.query.parse (st);
114 
115     } catch (Exception   e) {
116 
117         throw new JspException   ("Unable to parse statement: " +
118                     st,
119                     e);
120 
121     }
122 
123     return Tag.SKIP_BODY;
124 
125     }
126 
127     /**
128      * Execute the statement parsed in {@link #doAfterBody()}.
129      * The list of objects to execute the statement against is first retrieved
130      * using the value specified in {@link #setInputList(Object)}.  The list must
131      * not be null and must be a list otherwise an exception is thrown.
132      * <p>
133      * Once executed the results are set as an attribute specified by: 
134      * {@link #setResults(String)}.
135      * 
136      * @return {@link Tag#EVAL_PAGE} always.
137      * @throws JspException If the list is null, not a list or the statement cannot
138      *                      be executed against the list of objects.
139      */
140     public int doEndTag ()
141                      throws JspException  
142     {
143 
144     List   l = null;
145 
146     if (this.inputList instanceof String  )
147     {
148 
149         String   ln = (String  ) this.inputList;
150 
151         // Get the list.
152         Object   o = this.pageContext.findAttribute (ln);
153 
154         if (o == null)
155         {
156 
157         throw new JspException   ("No list with name: " +
158                     ln +
159                     " can be found");
160 
161         }
162 
163         if (!(o instanceof List  ))
164         {
165 
166         throw new JspException   ("Attribute: " +
167                     ln +
168                     " is not an instance of: " +
169                     List  .class.getName () + 
170                     ", is: " + 
171                     o.getClass ().getName ());
172 
173         }
174 
175         l = (List  ) o;
176 
177     }
178 
179     if (this.inputList instanceof List  )
180     {
181 
182         l = (List  ) this.inputList;
183 
184     }
185 
186     if (l == null)
187     {
188 
189         throw new JspException   ("No input list specified.");
190 
191     }
192 
193     try
194     {
195 
196         QueryResults qr = this.query.execute (l);
197 
198         // Set the query results as an attribute.
199         this.pageContext.setAttribute (this.results,
200                        qr);
201 
202     } catch (Exception   e) {
203 
204         throw new JspException   ("Unable to execute query with list: " +
205                     this.inputList,
206                     e);
207 
208     }
209 
210     return Tag.EVAL_PAGE;
211 
212     }
213 
214     /**
215      * Release the objects we have references to and then call: super.release ().
216      */
217     public void release ()
218     {
219 
220     this.inputList = null;
221     this.results = null;
222     this.query = null;
223     
224     super.release ();
225 
226     }
227 
228 }
229
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