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Reinier Zwitserloot
97 lines
6.0 KiB
HTML
97 lines
6.0 KiB
HTML
<!DOCTYPE html>
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<meta name="description" content="Spice up your java" />
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<title>@SneakyThrows</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>@SneakyThrows</h1>
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<div class="byline">To boldly throw checked exceptions where no one has thrown them before!</div>
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<div class="overview">
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<h3>Overview</h3>
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<p>
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<code>@SneakyThrows</code> can be used to sneakily throw checked exceptions without actually declaring this in your method's <code>throws</code>
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clause. This somewhat contentious ability should be used carefully, of course. The code generated by lombok will not ignore, wrap, replace,
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or otherwise modify the thrown checked exception; it simply fakes out the compiler. On the JVM (class file) level, all exceptions, checked or not,
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can be thrown regardless of the <code>throws</code> clause of your methods, which is why this works.
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</p><p>
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Common use cases for when you want to opt out of the checked exception mechanism center around 2 situations:<br /><ul>
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<li>A needlessly strict interface, such as <code>Runnable</code> - whatever exception propagates out of your <code>run()</code> method,
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checked or not, it will be passed to the <code>Thread</code>'s unhandled exception handler. Catching a checked exception and wrapping it
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in some sort of <code>RuntimeException</code> is only obscuring the real cause of the issue.</li>
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<li>An 'impossible' exception. For example, <code>new String(someByteArray, "UTF-8");</code> declares that it can throw an
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<code>UnsupportedEncodingException</code> but according to the JVM specification, UTF-8 <em>must</em> always be available. An
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<code>UnsupportedEncodingException</code> here is about as likely as a <code>ClassNotFoundError</code> when you use a String object,
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and you don't catch those either!</li></ul>
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</p><p>
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Be aware that it is <em>impossible</em> to catch sneakily thrown checked types directly, as javac will not let you write a catch block
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for an exception type that no method call in the try body declares as thrown. This problem is not relevant in either of the use cases listed
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above, so let this serve as a warning that you should not use the <code>@SneakyThrows</code> mechanism without some deliberation!
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</p><p>
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You can pass any number of exceptions to the <code>@SneakyThrows</code> annotation. If you pass no exceptions, you may throw any
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exception sneakily.
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</p><p>
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<em>NOTE: </em> with lombok versions older than 0.10, unlike other lombok transformations, you need to put <strong>lombok.jar</strong> on your
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classpath when you run your program.
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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.sneakyThrows.flagUsage</code> = [<code>warning</code> | <code>error</code>] (default: not set)</dt>
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<dd>Lombok will flag any usage of <code>@SneakyThrows</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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Because <code>@SneakyThrows</code> is an implementation detail and not part of your method signature, it is an error if you try to
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declare a checked exception as sneakily thrown when you don't call any methods that throw this exception. (Doing so is perfectly legal
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for <code>throws</code> statements to accommodate subclasses). Similarly, <code>@SneakyThrows</code> does not inherit.
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</p><p>
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For the nay-sayers in the crowd: Out of the box, Eclipse will offer a 'quick-fix' for uncaught exceptions that wraps the offending
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statement in a try/catch block with just <code>e.printStackTrace()</code> in the catch block. This is so spectacularly non-productive
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compared to just sneakily throwing the exception onwards, that Roel and Reinier feel more than justified in claiming that the
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checked exception system is far from perfect, and thus an opt-out mechanism is warranted.
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</p><p>
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If you put <code>@SneakyThrows</code> on a constructor, any call to a sibling or super constructor is <em>excluded</em> from the <code>@SneakyThrows</code> treatment. This is a
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java restriction we cannot work around: Calls to sibling/super constructors MUST be the first statement in the constructor; they cannot be placed inside try/catch blocks.
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</p><p>
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<code>@SneakyThrows</code> on an empty method, or a constructor that is empty or only has a call to a sibling / super constructor results in no try/catch block and a warning.
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<a href="index.html">Back to features</a> | <a href="Builder.html">Previous feature (@Builder)</a> | <a href="Synchronized.html">Next feature (@Synchronized)</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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