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diff --git a/website/features/SneakyThrows.html b/website/features/SneakyThrows.html new file mode 100644 index 00000000..b5d3194a --- /dev/null +++ b/website/features/SneakyThrows.html @@ -0,0 +1,78 @@ +<!DOCTYPE html> +<html><head> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> + <link rel="stylesheet" type="text/css" href="../logi/reset.css" /> + <link rel="stylesheet" type="text/css" href="features.css" /> + <link rel="shortcut icon" href="../favicon.ico" type="image/x-icon" /> + <meta name="description" content="Spice up your java" /> + <title>@SneakyThrows</title> + <!--[if lt IE 7]><script type="text/javascript" src="logi/iepngfix_tilebg.js"></script><![endif]--> +</head><body><div id="pepper"> + <div class="minimumHeight"></div> + <div class="meat"> + <div class="header"><a href="../index.html">Project Lombok</a></div> + <h1>@SneakyThrows</h1> + <div class="byline">To boldly throw checked exceptions where no one has thrown them before!</div> + <div class="overview"> + <h3>Overview</h3> + <p> + <code>@SneakyThrows</code> can be used to sneakily throw checked exceptions without actually declaring this in your method's <code>throws</code> + clause. This somewhat contentious ability should be used carefully, of course. The code generated by lombok will not ignore, wrap, replace, + or otherwise modify the thrown checked exception; it simply fakes out the compiler. On the JVM (class file) level, all exceptions, checked or not, + can be thrown regardless of the <code>throws</code> clause of your methods, which is why this works. + </p><p> + <em><strong>CAREFUL: </strong><em>Unlike other lombok transformations, you need to put <strong>lombok.jar</strong> on your classpath when + you run your program. + </p><p> + Common use cases for when you want to opt out of the checked exception mechanism center around 2 situations:<br /><li> + <ul>A needlessly strict interface, such as <code>Runnable</code> - whatever exception propagates out of your <code>run()</code> method, + checked or not, it will be passed to the <code>Thread</code>'s unhandled exception handler. Catching a checked exception and wrapping it + in some sort of <code>RuntimeException</code> is only obscuring the real cause of the issue.</ul> + <ul>An 'impossible' exception. For example, <code>new String(someByteArray, "UTF-8");</code> declares that it can throw an + <code>UnsupportedEncodingException</code> but according to the JVM specification, UTF-8 <em>must</em> always be available. An + <code>UnsupportedEncodingException</code> here is about as likely as a <code>ClassNotFoundError</code> when you use a String object, + and you don't catch those either!</ul> + </p><p> + 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 + 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 + above, so let this serve as a warning that you should not use the <code>@SneakyThrows</code> mechanism without some deliberation! + </p><p> + You can pass any number of exceptions to the <code>@SneakyThrows</code> annotation. If you pass no exceptions, you may throw any + exception sneakily. + </div> + <div class="snippets"> + <div class="pre"> + <h3>With Lombok</h3> + <div class="snippet">@HTML_PRE@</div> + </div> + <div class="sep"></div> + <div class="post"> + <h3>Vanilla Java</h3> + <div class="snippet">@HTML_POST@</div> + </div> + </div> + <div style="clear: left;"></div> + <div class="overview"> + <h3>Small print</h3><div class="smallprint"> + <p> + Because <code>@SneakyThrows</code> is an implementation detail and not part of your method signature, it is an error if you try to + declare a checked exception as sneakily thrown when you don't call any methods that throw this exception. (Doing so is perfectly legal + for <code>throws</code> statements to accomodate subclasses). Similarly, <code>@SneakyThrows</code> does not inherit. + </p><p> + For the nay-sayers in the crowd: Out of the box, Eclipse will offer a 'quick-fix' for uncaught exceptions that wraps the offending + statement in a try/catch block with just <code>e.printStackTrace()</code> in the catch block. This is so spectacularly non-productive + compared to just sneakily throwing the exception onwards, that Roel and Reinier feel more than justified in claiming that the + checked exception system is far from perfect, and thus an opt-out mechanism is warranted. + </p><p> + Currently usage of <code>@SneakyThrows</code> requires you to have <code>lombok.jar</code> in the classpath at runtime. However, in the future + we will attempt to eliminate this requirement - when we figure out how we can do that. If anyone has a good idea on how to make that happen, let us know! + </p> + </div> + </div> + <div class="footer"> + <a href="index.html">Back to features</a> | <a href="Synchronized.html">Previous feature (@Synchronized)</a> | <span class="disabled">Next feature</span><br /> + <span class="copyright">Copyright © 2009 Reinier Zwitserloot and Roel Spilker, licensed under the <a href="http://www.opensource.org/licenses/mit-license.php">MIT licence</a>.</span> + </div> + <div style="clear: both;"></div> + </div> +</div></body></html> |