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<span id="id1"></span><h1>表达式核心变量<a class="headerlink" href="#" title="永久链接至标题">¶</a></h1>
<p>无论是匹配表达式也好、观察表达式也罢，他们核心判断变量都是围绕着一个 Arthas 中的通用通知对象 <tt class="docutils literal">Advice</tt> 进行。</p>
<p>它的简略代码结构如下</p>
<div class="highlight-java notranslate"><div class="highlight hljs"><pre class="java">public class Advice {
private final ClassLoader loader;
private final Class<?> clazz;
private final ArthasMethod method;
private final Object target;
private final Object[] params;
private final Object returnObj;
private final Throwable throwExp;
private final boolean isBefore;
private final boolean isThrow;
private final boolean isReturn;
// getter/setter
}
</pre></div>
</div>
<p>这里列一个表格来说明不同变量的含义</p>
<table border="1" class="docutils">
<thead>
<tr>
<th align="right">变量名</th>
<th align="left">变量解释</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right">loader</td>
<td align="left">本次调用类所在的 ClassLoader</td>
</tr>
<tr>
<td align="right">clazz</td>
<td align="left">本次调用类的 Class 引用</td>
</tr>
<tr>
<td align="right">method</td>
<td align="left">本次调用方法反射引用</td>
</tr>
<tr>
<td align="right">target</td>
<td align="left">本次调用类的实例</td>
</tr>
<tr>
<td align="right">params</td>
<td align="left">本次调用参数列表，这是一个数组，如果方法是无参方法则为空数组</td>
</tr>
<tr>
<td align="right">returnObj</td>
<td align="left">本次调用返回的对象。当且仅当 <code>isReturn==true</code> 成立时候有效，表明方法调用是以正常返回的方式结束。如果当前方法无返回值 <code>void</code>，则值为 null</td>
</tr>
<tr>
<td align="right">throwExp</td>
<td align="left">本次调用抛出的异常。当且仅当 <code>isThrow==true</code> 成立时有效，表明方法调用是以抛出异常的方式结束。</td>
</tr>
<tr>
<td align="right">isBefore</td>
<td align="left">辅助判断标记，当前的通知节点有可能是在方法一开始就通知，此时 <code>isBefore==true</code> 成立，同时 <code>isThrow==false</code> 和 <code>isReturn==false</code>，因为在方法刚开始时，还无法确定方法调用将会如何结束。</td>
</tr>
<tr>
<td align="right">isThrow</td>
<td align="left">辅助判断标记，当前的方法调用以抛异常的形式结束。</td>
</tr>
<tr>
<td align="right">isReturn</td>
<td align="left">辅助判断标记，当前的方法调用以正常返回的形式结束。</td>
</tr>
</tbody>
</table><p>所有变量都可以在表达式中直接使用，如果在表达式中编写了不符合 OGNL 脚本语法或者引入了不在表格中的变量，则退出命令的执行；用户可以根据当前的异常信息修正<tt class="docutils literal">条件表达式</tt>或<tt class="docutils literal">观察表达式</tt></p>
<ul class="simple">
<li>特殊用法请参考：<a class="reference external" href="https://github.com/alibaba/arthas/issues/71">https://github.com/alibaba/arthas/issues/71</a></li>
<li>OGNL表达式官网：<a class="reference external" href="https://commons.apache.org/proper/commons-ognl/language-guide.html">https://commons.apache.org/proper/commons-ognl/language-guide.html</a></li>
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