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Reinier Zwitserloot
87 lines
4.6 KiB
HTML
87 lines
4.6 KiB
HTML
<!DOCTYPE html>
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<html><head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<link rel="stylesheet" type="text/css" href="../logi/reset.css" />
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<link rel="stylesheet" type="text/css" href="features.css" />
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<link rel="shortcut icon" href="../favicon.ico" type="image/x-icon" />
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<meta name="description" content="Spice up your java" />
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<title>@Cleanup</title>
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</head><body><div id="pepper">
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<div class="minimumHeight"></div>
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<div class="meat">
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<div class="header"><a href="../index.html">Project Lombok</a></div>
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<h1>@Cleanup</h1>
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<div class="byline">Automatic resource management: Call your <code>close()</code> methods safely with no hassle.</div>
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<div class="overview">
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<h3>Overview</h3>
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<p>
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You can use <code>@Cleanup</code> to ensure a given resource is automatically cleaned up before the code execution path exits your
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current scope. You do this by annotating any local variable declaration with the <code>@Cleanup</code> annotation like so:<br />
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<code>@Cleanup InputStream in = new FileInputStream("some/file");</code><br />
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As a result, at the end of the scope you're in, <code>in.close()</code> is called. This call is guaranteed to run by way of a
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try/finally construct. Look at the example below to see how this works.
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</p><p>
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If the type of object you'd like to cleanup does not have a <code>close()</code> method, but some other no-argument method, you can
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specify the name of this method like so:<br />
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<code>@Cleanup("dispose") org.eclipse.swt.widgets.CoolBar bar = new CoolBar(parent, 0);</code><br />
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By default, the cleanup method is presumed to be <code>close()</code>. A cleanup method that takes 1 or more arguments cannot be called via
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<code>@Cleanup</code>.
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</p>
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</div>
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<div class="snippets">
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<div class="pre">
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<h3>With Lombok</h3>
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<div class="snippet">@HTML_PRE@</div>
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</div>
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<div class="sep"></div>
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<div class="post">
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<h3>Vanilla Java</h3>
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<div class="snippet">@HTML_POST@</div>
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</div>
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</div>
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<div style="clear: left;"></div>
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<div class="overview confKeys">
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<h3>Supported configuration keys:</h3>
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<dl>
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<dt><code>lombok.cleanup.flagUsage</code> = [<code>warning</code> | <code>error</code>] (default: not set)</dt>
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<dd>Lombok will flag any usage of <code>@Cleanup</code> as a warning or error if configured.</dd>
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</dl>
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</div>
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<div class="overview">
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<h3>Small print</h3><div class="smallprint">
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<p>
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In the finally block, the cleanup method is only called if the given resource is not <code>null</code>. However, if you use <code>delombok</code>
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on the code, a call to <code>lombok.Lombok.preventNullAnalysis(Object o)</code> is inserted to prevent warnings if static code analysis could
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determine that a null-check would not be needed. Compilation with <code>lombok.jar</code> on the classpath removes that method call,
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so there is no runtime dependency.
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</p>
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<p>
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If your code throws an exception, and the cleanup method call that is then triggered also throws an exception, then the original exception
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is hidden by the exception thrown by the cleanup call. You should <em>not</em> rely on this 'feature'. Preferably, lombok would like to generate
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code so that, if the main body has thrown an exception, any exception thrown by the close call is silently swallowed (but if the main body
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exited in any other way, exceptions by the close call will not be swallowed). The authors of lombok do not currently know of a feasible way
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to implement this scheme, but if java updates allow it, or we find a way, we'll fix it.
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</p><p>
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You do still need to handle any exception that the cleanup method can generate!
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</p>
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</div>
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</div>
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<div class="footer">
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<a href="index.html">Back to features</a> | <a href="NonNull.html">Previous feature (@NonNull)</a> | <a href="GetterSetter.html">Next feature (@Getter / @Setter)</a><br />
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<a href="../credits.html" class="creditsLink">credits</a> | <span class="copyright">Copyright © 2009-2015 The Project Lombok Authors, licensed under the <a href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>.</span>
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