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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: Recover</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'defer';
}
if (e.key == "ArrowRight") {
window.location.href = 'string-functions';
}
}
</script>
<body>
<div class="example" id="recover">
<h2><a href="./">Go by Example 中文版</a>: Recover</h2>
<table>
<tr>
<td class="docs">
<p>Go 通过使用 <code>recover</code> 内置函数，可以从 panic 中 <em>恢复recover</em> 。
<code>recover</code> 可以阻止 <code>panic</code> 中止程序，并让它继续执行。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
<p>在这样的例子中很有用：当其中一个客户端连接出现严重错误，服务器不希望崩溃。
相反，服务器希望关闭该连接并继续为其他的客户端提供服务。
实际上，这就是Go的 <code>net/http</code> 包默认对于 HTTP 服务器的处理。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/hWKbYiQosMj"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这是一个 panic 函数</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">mayPanic</span><span class="p">()</span> <span class="p">{</span>
<span class="nb">panic</span><span class="p">(</span><span class="s">"a problem"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>必须在 defer 函数中调用 <code>recover</code>。
当跳出引发 panic 的函数时，defer 会被激活，
其中的 <code>recover</code> 会捕获 <code>panic</code>。</p>
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>recover</code> 的返回值是在调用 <code>panic</code> 时抛出的错误。</p>
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">defer</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">r</span> <span class="o">:=</span> <span class="nb">recover</span><span class="p">();</span> <span class="nx">r</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Recovered. Error:\n"</span><span class="p">,</span> <span class="nx">r</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nf">mayPanic</span><span class="p">()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这行代码不会执行，因为 mayPanic 函数会调用 <code>panic</code>。
<code>main</code> 程序的执行在 <code>panic</code> 点停止，并在继续处理完 <code>defer</code> 后结束。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"After mayPanic()"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="go">Recovered. Error:
</span><span class="go"> a problem</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="string-functions">字符串函数</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
<script>
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codeLines.push('');codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func mayPanic() {\u000A panic(\"a problem\")\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' defer func() {\u000A if r :\u003D recover(); r !\u003D nil {\u000A');codeLines.push(' fmt.Println(\"Recovered. Error:\\n\", r)\u000A }\u000A }()\u000A');codeLines.push(' mayPanic()\u000A');codeLines.push(' fmt.Println(\"After mayPanic()\")\u000A}\u000A');codeLines.push('');
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</body>
</html>