TryCatchTask


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48  package net.sf.antcontrib.logic;
49  
50  import org.apache.tools.ant.BuildException;
51  import org.apache.tools.ant.Project;
52  import org.apache.tools.ant.Task;
53  import org.apache.tools.ant.taskdefs.Sequential;
54  
55  /**
56   * A wrapper that lets you run a set of tasks and optionally run a
57   * different set of tasks if the first set fails and yet another set
58   * after the first one has finished.
59   *
60   * <p>This mirrors Java's try/catch/finally.</p>
61   *
62   * <p>The tasks inside of the required <code>&lt;try&gt;</code>
63   * element will be run.  If one of them should throw a {@link
64   * org.apache.tools.ant.BuildException BuildException} several things
65   * can happen:</p>
66   *
67   * <ul>
68   *   <li>If there is no <code>&lt;catch&gt;</code> block, the
69   *   exception will be passed through to Ant.</li>
70   *
71   *   <li>If the property attribute has been set, a property of the
72   *   given name will be set to the message of the exception.</li>
73   *
74   *   <li>If the reference attribute has been set, a reference of the
75   *   given id will be created and point to the exception object.</li>
76   *
77   *   <li>If there is a <code>&lt;catch&gt;</code> block, the tasks
78   *   nested into it will be run.</li>
79   * </ul>
80   *
81   * <p>If a <code>&lt;finally&gt;</code> block is present, the task
82   * nested into it will be run, no matter whether the first tasks have
83   * thrown an exception or not.</p>
84   *
85   * <p><strong>Attributes:</strong></p>
86   *
87   * <table>
88   *   <tr>
89   *     <td>Name</td>
90   *     <td>Description</td>
91   *     <td>Required</td>
92   *   </tr>
93   *   <tr>
94   *     <td>property</td>
95   *     <td>Name of a property that will receive the message of the
96   *     exception that has been caught (if any)</td>
97   *     <td>No</td>
98   *   </tr>
99   *   <tr>
100  *     <td>reference</td>
101  *     <td>Id of a reference that will point to the exception object
102  *     that has been caught (if any)</td>
103  *     <td>No</td>
104  *   </tr>
105  * </table>
106  *
107  * <p>Use the following task to define the <code>&lt;trycatch&gt;</code>
108  * task before you use it the first time:</p>
109  *
110  * <pre><code>
111  *   &lt;taskdef name="trycatch" 
112  *            classname="net.sf.antcontrib.logic.TryCatchTask" /&gt;
113  * </code></pre>
114  * 
115  * <h3>Crude Example</h3>
116  *
117  * <pre><code>
118  * &lt;trycatch property=&quot;foo&quot; reference=&quot;bar&quot;&gt;
119  *   &lt;try&gt;
120  *     &lt;fail&gt;Tada!&lt;/fail&gt;
121  *   &lt;/try&gt;
122  *
123  *   &lt;catch&gt;
124  *     &lt;echo&gt;In &amp;lt;catch&amp;gt;.&lt;/echo&gt;
125  *   &lt;/catch&gt;
126  *
127  *   &lt;finally&gt;
128  *     &lt;echo&gt;In &amp;lt;finally&amp;gt;.&lt;/echo&gt;
129  *   &lt;/finally&gt;
130  * &lt;/trycatch&gt;
131  *
132  * &lt;echo&gt;As property: ${foo}&lt;/echo&gt;
133  * &lt;property name=&quot;baz&quot; refid=&quot;bar&quot; /&gt;
134  * &lt;echo&gt;From reference: ${baz}&lt;/echo&gt;
135  * </code></pre>
136  *
137  * <p>results in</p>
138  *
139  * <pre><code>
140  *   [trycatch] Caught exception: Tada!
141  *       [echo] In &lt;catch&gt;.
142  *       [echo] In &lt;finally&gt;.
143  *       [echo] As property: Tada!
144  *       [echo] From reference: Tada!
145  * </code></pre>
146  *
147  * @author <a HREF="mailto:stefan.bodewig@epost.de">Stefan Bodewig</a>
148  * @author <a HREF="mailto:RITCHED2@Nationwide.com">Dan Ritchey</a>
149  */
150 public class TryCatchTask extends Task {
151 
152     private Sequential tryTasks = null;
153     private Sequential catchTasks = null;
154     private Sequential finallyTasks = null;
155     private String   property = null;
156     private String   reference = null;
157 
158     /**
159      * Adds a nested &lt;try&gt; block - one is required, more is
160      * forbidden.
161      */
162     public void addTry(Sequential seq) throws BuildException {
163         if (tryTasks != null) {
164             throw new BuildException("You must not specify more than one <try>");
165         }
166         
167         tryTasks = seq;
168     }
169 
170     /**
171      * Adds a nested &lt;catch&gt; block - at most one is allowed.
172      */
173     public void addCatch(Sequential seq) throws BuildException {
174         if (catchTasks != null) {
175             throw new BuildException("You must not specify more than one <catch>");
176         }
177         
178         catchTasks = seq;
179     }
180 
181     /**
182      * Adds a nested &lt;finally&gt; block - at most one is allowed.
183      */
184     public void addFinally(Sequential seq) throws BuildException {
185         if (finallyTasks != null) {
186             throw new BuildException("You must not specify more than one <finally>");
187         }
188         
189         finallyTasks = seq;
190     }
191 
192     /**
193      * Sets the property attribute.
194      */
195     public void setProperty(String   p) {
196         property = p;
197     }
198 
199     /**
200      * Sets the reference attribute.
201      */
202     public void setReference(String   r) {
203         reference = r;
204     }
205 
206     /**
207      * The heart of the task.
208      */
209     public void execute() throws BuildException {
210         if (tryTasks == null) {
211             throw new BuildException("A nested <try> element is required");
212         }
213 
214         try {
215             tryTasks.perform();
216         } catch (BuildException e) {
217             if (property != null) {
218                 /*
219                  * Using setProperty instead of setNewProperty to
220                  * be able to compile with Ant < 1.5.
221                  */
222                 project.setProperty(property, e.getMessage());
223             }
224             
225             if (reference != null) {
226                 project.addReference(reference, e);
227             }
228             
229             if (catchTasks == null) {
230                 throw e;
231             } else {
232                 log("Caught exception: "+e.getMessage(), Project.MSG_INFO);
233                 catchTasks.perform();
234             }
235         } finally {
236             if (finallyTasks != null) {
237                 finallyTasks.perform();
238             }
239         }
240     }
241 
242 }
243
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