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Posted to commits@aries.apache.org by bu...@apache.org on 2016/05/17 17:20:54 UTC
svn commit: r988470 - in /websites/staging/aries/trunk/content: ./
modules/tx-control/exceptionManagement.html modules/tx-control/index.html
Author: buildbot
Date: Tue May 17 17:20:54 2016
New Revision: 988470
Log:
Staging update by buildbot for aries
Added:
websites/staging/aries/trunk/content/modules/tx-control/exceptionManagement.html
Modified:
websites/staging/aries/trunk/content/ (props changed)
websites/staging/aries/trunk/content/modules/tx-control/index.html
Propchange: websites/staging/aries/trunk/content/
------------------------------------------------------------------------------
--- cms:source-revision (original)
+++ cms:source-revision Tue May 17 17:20:54 2016
@@ -1 +1 @@
-1743006
+1744294
Added: websites/staging/aries/trunk/content/modules/tx-control/exceptionManagement.html
==============================================================================
--- websites/staging/aries/trunk/content/modules/tx-control/exceptionManagement.html (added)
+++ websites/staging/aries/trunk/content/modules/tx-control/exceptionManagement.html Tue May 17 17:20:54 2016
@@ -0,0 +1,372 @@
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+ It was originally lifted from http://subversion.apache.org/style/site.css */
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+<h1 id="exception-management">Exception Management<a class="headerlink" href="#exception-management" title="Permanent link">¶</a></h1>
+<p>Managing Exceptions should not be a core part of your business logic. In fact with the Transaction Control
+Service is doing its job you shouldn't need to worry about exceptions at all! A key design goal for the
+Transaction Control Service is to avoid the need for try/catch/finally blocks as far as possible.</p>
+<h2 id="throwing-exceptions-from-scoped-work">Throwing Exceptions from scoped work<a class="headerlink" href="#throwing-exceptions-from-scoped-work" title="Permanent link">¶</a></h2>
+<p>Resources can be tempramental sometimes, and usually have defined exceptions that are thrown in certain
+error cases. These can be generic, like <code>SQLException</code> or <code>JMSException</code>,
+or specific like <code>EntityNotFoundException</code>.</p>
+<p>In any event - exceptions indicate that a problem has occurred. By default an exception thrown from inside a
+transactional scope will cause the transaction to roll back. This means that the code can safely ignore any
+updates that were made. Furthermore, because a piece of scoped work is defined as a <code>Callable</code>
+it is not necessary to catch or wrap an Exception raised in a scope.</p>
+<div class="codehilite"><pre><span class="c1">// An SQLException may be raised by the query, </span>
+<span class="c1">// but we don't need to catch it</span>
+<span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-></span> <span class="n">connection</span><span class="p">.</span><span class="n">createStatement</span><span class="p">()</span>
+ <span class="p">.</span><span class="n">executeQuery</span><span class="p">(</span><span class="s">"Insert into TEST_TABLE values ( 'Hello World!' )"</span><span class="p">));</span>
+</pre></div>
+
+
+<h2 id="catching-exceptions-thrown-from-scoped-work">Catching Exceptions thrown from scoped work<a class="headerlink" href="#catching-exceptions-thrown-from-scoped-work" title="Permanent link">¶</a></h2>
+<p>In general Exceptions should not form part of your client API, so catching an Exception from a piece of scoped
+work is rarely necessary. Usually exceptions generated by scoped work are eventually handled by catch all
+collectors at the incoming request point (for example a servlet) and do not require special handling.</p>
+<p>Sometimes, however, we have to work within an existing API that <em>does</em> use an Exception as a type of
+return value. In that case it is important to know what happened to the Exception.</p>
+<h3 id="the-scopedworkexception">The <code>ScopedWorkException</code><a class="headerlink" href="#the-scopedworkexception" title="Permanent link">¶</a></h3>
+<p>Scoped work is free to throw checked or unchecked Exceptions, however these Exceptions cannot be directly
+thrown on by the TransactionControl implementation. The primary reason for this is that directly rethrowing the
+Exception would force users of the Transaction Control Service to either <em>always</em> declare
+<code>throws Exception</code> on their methods or to add try/catch blocks around every call.</p>
+<p>Exceptions generated as part of Scoped Work are therefore wrapped by the Transaction Control Service in a
+<code>ScopedWorkException</code>. <code>ScopedWorkException</code> is an <em>unchecked exception</em>
+and so can be ignored by your component if it does not require special handling (the typical case).</p>
+<h3 id="unwrapping-the-scopedworkexception">Unwrapping the <code>ScopedWorkException</code><a class="headerlink" href="#unwrapping-the-scopedworkexception" title="Permanent link">¶</a></h3>
+<p>As mentioned above, sometimes it is necessary for an API to throw a particular type of Exception as a return value.</p>
+<p>This model can be supported by unwrapping the ScopedWorkException.</p>
+<div class="codehilite"><pre><span class="k">try</span> <span class="p">{</span>
+ <span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-></span> <span class="n">connection</span><span class="p">.</span><span class="n">createStatement</span><span class="p">()</span>
+ <span class="p">.</span><span class="n">executeQuery</span><span class="p">(</span>"<span class="n">Insert</span> <span class="n">into</span> <span class="n">TEST_TABLE</span> <span class="n">values</span> <span class="p">(</span> <span class="s">'Hello World!'</span> <span class="p">)</span>"<span class="p">));</span>
+<span class="p">}</span> <span class="k">catch</span> <span class="p">(</span><span class="n">ScopedWorkException</span> <span class="n">swe</span><span class="p">)</span> <span class="p">{</span>
+ <span class="o">//</span> <span class="n">This</span> <span class="n">line</span> <span class="n">throws</span> <span class="n">the</span> <span class="n">cause</span> <span class="n">of</span> <span class="n">the</span> <span class="n">ScopedWorkException</span> <span class="n">as</span>
+ <span class="o">//</span> <span class="n">an</span> <span class="n">SQLException</span> <span class="n">or</span> <span class="n">as</span> <span class="n">a</span> <span class="n">RuntimeException</span> <span class="k">if</span> <span class="n">appropriate</span>
+ <span class="n">throw</span> <span class="n">swe</span><span class="p">.</span><span class="n">as</span><span class="p">(</span><span class="n">SQLException</span><span class="p">.</span><span class="n">class</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+
+
+<p>This mechanism also supports multiple Exception types:</p>
+<div class="codehilite"><pre><span class="k">try</span> <span class="p">{</span>
+ <span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-></span> <span class="n">connection</span><span class="p">.</span><span class="n">createStatement</span><span class="p">()</span>
+ <span class="p">.</span><span class="n">executeQuery</span><span class="p">(</span>"<span class="n">Insert</span> <span class="n">into</span> <span class="n">TEST_TABLE</span> <span class="n">values</span> <span class="p">(</span> <span class="s">'Hello World!'</span> <span class="p">)</span>"<span class="p">));</span>
+<span class="p">}</span> <span class="k">catch</span> <span class="p">(</span><span class="n">ScopedWorkException</span> <span class="n">swe</span><span class="p">)</span> <span class="p">{</span>
+ <span class="o">//</span> <span class="n">This</span> <span class="n">line</span> <span class="n">throws</span> <span class="n">the</span> <span class="n">cause</span> <span class="n">of</span> <span class="n">the</span> <span class="n">ScopedWorkException</span>
+ <span class="o">//</span> <span class="n">as</span> <span class="n">one</span> <span class="n">of</span> <span class="n">the</span> <span class="n">two</span> <span class="n">SQLException</span> <span class="n">types</span> <span class="n">or</span> <span class="n">as</span> <span class="n">a</span>
+ <span class="o">//</span> <span class="n">RuntimeException</span> <span class="k">if</span> <span class="n">appropriate</span>
+ <span class="n">throw</span> <span class="n">swe</span><span class="p">.</span><span class="n">asOneOf</span><span class="p">(</span><span class="n">SQLRecoverableException</span><span class="p">.</span><span class="n">class</span><span class="p">,</span> <span class="n">SQLTransientException</span><span class="p">.</span><span class="n">class</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+
+
+<p>Note that if you unwrap a <code>ScopedWorkException</code> into a checked exception then you will have
+to list that Exception in your <code>throws</code> clause.</p></div>
+ <!-- Content -->
+ </td>
+ </tr>
+ </table>
+ </td>
+ <td id="cell-2-2" colspan="2"> </td>
+ </tr>
+ <tr width="100%">
+ <td id="cell-3-0"> </td>
+ <td id="cell-3-1"> </td>
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+ <td id="cell-4-2" colspan="2"> </td>
+ </tr>
+</table>
+</body>
+</html>
Modified: websites/staging/aries/trunk/content/modules/tx-control/index.html
==============================================================================
--- websites/staging/aries/trunk/content/modules/tx-control/index.html (original)
+++ websites/staging/aries/trunk/content/modules/tx-control/index.html Tue May 17 17:20:54 2016
@@ -309,6 +309,7 @@ transactional resource access</p>
<li><a href="lastResourceGambit.html">Making use of the Last Resource Gambit</a></li>
<li><a href="advancedResourceProviders.html">Custom Resource Providers</a></li>
<li><a href="advancedScopes.html">Advanced Scope control</a></li>
+<li><a href="exceptionManagement.html">Exception Management</a></li>
</ul></div>
<!-- Content -->
</td>