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<li class="toctree-l4"><a class="reference internal" href="#">同时观察方法调用前和方法返回后</a></li>
<li class="toctree-l4"><a class="reference internal" href="#x">调整<tt class="docutils literal">-x</tt>的值，观察具体的方法参数值</a></li>
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<div class="section" id="watch">
<span id="watch"></span><h1>watch<a class="headerlink" href="#watch" title="永久链接至标题">¶</a></h1>
<blockquote>
<div>方法执行数据观测</div></blockquote>
<p>让你能方便的观察到指定方法的调用情况。能观察到的范围为：<tt class="docutils literal">返回值</tt>、<tt class="docutils literal">抛出异常</tt>、<tt class="docutils literal">入参</tt>，通过编写 OGNL 表达式进行对应变量的查看。</p>
<div class="section" id="">
<span id="id1"></span><h2>参数说明<a class="headerlink" href="#" title="永久链接至标题">¶</a></h2>
<p>watch 的参数比较多，主要是因为它能在 4 个不同的场景观察对象</p>
<table border="1" class="docutils">
<thead>
<tr>
<th align="right">参数名称</th>
<th align="left">参数说明</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right"><em>class-pattern</em></td>
<td align="left">类名表达式匹配</td>
</tr>
<tr>
<td align="right"><em>method-pattern</em></td>
<td align="left">方法名表达式匹配</td>
</tr>
<tr>
<td align="right"><em>express</em></td>
<td align="left">观察表达式</td>
</tr>
<tr>
<td align="right"><em>condition-express</em></td>
<td align="left">条件表达式</td>
</tr>
<tr>
<td align="right">[b]</td>
<td align="left">在<strong>方法调用之前</strong>观察</td>
</tr>
<tr>
<td align="right">[e]</td>
<td align="left">在<strong>方法异常之后</strong>观察</td>
</tr>
<tr>
<td align="right">[s]</td>
<td align="left">在<strong>方法返回之后</strong>观察</td>
</tr>
<tr>
<td align="right">[f]</td>
<td align="left">在<strong>方法结束之后</strong>(正常返回和异常返回)观察</td>
</tr>
<tr>
<td align="right">[E]</td>
<td align="left">开启正则表达式匹配，默认为通配符匹配</td>
</tr>
<tr>
<td align="right">[x:]</td>
<td align="left">指定输出结果的属性遍历深度，默认为 1</td>
</tr>
</tbody>
</table><p>这里重点要说明的是观察表达式，观察表达式的构成主要由 ognl 表达式组成，所以你可以这样写<tt class="docutils literal">"{params,returnObj}"</tt>，只要是一个合法的 ognl 表达式，都能被正常支持。</p>
<p>观察的维度也比较多，主要体现在参数 <tt class="docutils literal">advice</tt> 的数据结构上。<tt class="docutils literal">Advice</tt> 参数最主要是封装了通知节点的所有信息。请参考<a class="reference internal" href="advice-class.html"><span class="doc">表达式核心变量</span></a>中关于该节点的描述。</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>
</ul>
<p><strong>特别说明</strong>：</p>
<ul class="simple">
<li>watch 命令定义了4个观察事件点，即 <tt class="docutils literal">-b</tt> 方法调用前，<tt class="docutils literal">-e</tt> 方法异常后，<tt class="docutils literal">-s</tt> 方法返回后，<tt class="docutils literal">-f</tt> 方法结束后</li>
<li>4个观察事件点 <tt class="docutils literal">-b</tt>、<tt class="docutils literal">-e</tt>、<tt class="docutils literal">-s</tt> 默认关闭，<tt class="docutils literal">-f</tt> 默认打开，当指定观察点被打开后，在相应事件点会对观察表达式进行求值并输出</li>
<li>这里要注意<tt class="docutils literal">方法入参</tt>和<tt class="docutils literal">方法出参</tt>的区别，有可能在中间被修改导致前后不一致，除了 <tt class="docutils literal">-b</tt> 事件点 <tt class="docutils literal">params</tt> 代表方法入参外，其余事件都代表方法出参</li>
<li>当使用 <tt class="docutils literal">-b</tt> 时，由于观察事件点是在方法调用前，此时返回值或异常均不存在</li>
</ul>
</div>
<div class="section" id="">
<span id="id2"></span><h2>使用参考<a class="headerlink" href="#" title="永久链接至标题">¶</a></h2>
<div class="section" id="demo">
<span id="demo"></span><h3>启动 Demo<a class="headerlink" href="#demo" title="永久链接至标题">¶</a></h3>
<p>启动<a class="reference internal" href="quick-start.html"><span class="doc">快速入门</span></a>里的<tt class="docutils literal">arthas-demo</tt>。</p>
</div>
<div class="section" id="">
<span id="id3"></span><h3>观察方法出参和返回值<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors "{params,returnObj}" -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 44 ms.
ts=2018-12-03 19:16:51; [cost=1.280502ms] result=@ArrayList[
@Object[][
@Integer[535629513],
],
@ArrayList[
@Integer[3],
@Integer[19],
@Integer[191],
@Integer[49199],
],
]
</pre></div>
</div>
</div>
<div class="section" id="">
<span id="id4"></span><h3>观察方法入参<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors "{params,returnObj}" -x 2 -b
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 50 ms.
ts=2018-12-03 19:23:23; [cost=0.0353ms] result=@ArrayList[
@Object[][
@Integer[-1077465243],
],
null,
]
</pre></div>
</div>
<ul class="simple">
<li>对比前一个例子，返回值为空（事件点为方法执行前，因此获取不到返回值）</li>
</ul>
</div>
<div class="section" id="">
<span id="id5"></span><h3>同时观察方法调用前和方法返回后<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors "{params,target,returnObj}" -x 2 -b -s -n 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 46 ms.
ts=2018-12-03 19:29:54; [cost=0.01696ms] result=@ArrayList[
@Object[][
@Integer[1544665400],
],
@MathGame[
random=@Random[java.util.Random@522b408a],
illegalArgumentCount=@Integer[13038],
],
null,
]
ts=2018-12-03 19:29:54; [cost=4.277392ms] result=@ArrayList[
@Object[][
@Integer[1544665400],
],
@MathGame[
random=@Random[java.util.Random@522b408a],
illegalArgumentCount=@Integer[13038],
],
@ArrayList[
@Integer[2],
@Integer[2],
@Integer[2],
@Integer[5],
@Integer[5],
@Integer[73],
@Integer[241],
@Integer[439],
],
]
</pre></div>
</div>
<ul class="simple">
<li>参数里<tt class="docutils literal">-n 2</tt>，表示只执行两次</li>
<li>这里输出结果中，第一次输出的是方法调用前的观察表达式的结果，第二次输出的是方法返回后的表达式的结果</li>
<li>结果的输出顺序和事件发生的先后顺序一致，和命令中 <tt class="docutils literal">-s -b</tt> 的顺序无关</li>
</ul>
</div>
<div class="section" id="x">
<span id="x"></span><h3>调整<tt class="docutils literal">-x</tt>的值，观察具体的方法参数值<a class="headerlink" href="#x" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors "{params,target}" -x 3
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 58 ms.
ts=2018-12-03 19:34:19; [cost=0.587833ms] result=@ArrayList[
@Object[][
@Integer[47816758],
],
@MathGame[
random=@Random[
serialVersionUID=@Long[3905348978240129619],
seed=@AtomicLong[3133719055989],
multiplier=@Long[25214903917],
addend=@Long[11],
mask=@Long[281474976710655],
DOUBLE_UNIT=@Double[1.1102230246251565E-16],
BadBound=@String[bound must be positive],
BadRange=@String[bound must be greater than origin],
BadSize=@String[size must be non-negative],
seedUniquifier=@AtomicLong[-3282039941672302964],
nextNextGaussian=@Double[0.0],
haveNextNextGaussian=@Boolean[false],
serialPersistentFields=@ObjectStreamField[][isEmpty=false;size=3],
unsafe=@Unsafe[sun.misc.Unsafe@2eaa1027],
seedOffset=@Long[24],
],
illegalArgumentCount=@Integer[13159],
],
]
</pre></div>
</div>
<ul class="simple">
<li><tt class="docutils literal">-x</tt>表示遍历深度，可以调整来打印具体的参数和结果内容，默认值是1。</li>
</ul>
</div>
<div class="section" id="">
<span id="id6"></span><h3>条件表达式的例子<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors "{params[0],target}" "params[0]<0"
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 68 ms.
ts=2018-12-03 19:36:04; [cost=0.530255ms] result=@ArrayList[
@Integer[-18178089],
@MathGame[demo.MathGame@41cf53f9],
]
</pre></div>
</div>
<ul class="simple">
<li>只有满足条件的调用，才会有响应。</li>
</ul>
</div>
<div class="section" id="">
<span id="id7"></span><h3>观察异常信息的例子<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors "{params[0],throwExp}" -e -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 62 ms.
ts=2018-12-03 19:38:00; [cost=1.414993ms] result=@ArrayList[
@Integer[-1120397038],
java.lang.IllegalArgumentException: number is: -1120397038, need >= 2
at demo.MathGame.primeFactors(MathGame.java:46)
at demo.MathGame.run(MathGame.java:24)
at demo.MathGame.main(MathGame.java:16)
,
]
</pre></div>
</div>
<ul class="simple">
<li><tt class="docutils literal">-e</tt>表示抛出异常时才触发</li>
<li>express中，表示异常信息的变量是<tt class="docutils literal">throwExp</tt></li>
</ul>
</div>
<div class="section" id="">
<span id="id8"></span><h3>按照耗时进行过滤<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors '{params, returnObj}' '#cost>200' -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 66 ms.
ts=2018-12-03 19:40:28; [cost=2112.168897ms] result=@ArrayList[
@Object[][
@Integer[2141897465],
],
@ArrayList[
@Integer[5],
@Integer[428379493],
],
]
</pre></div>
</div>
<ul class="simple">
<li><tt class="docutils literal">#cost>200</tt>(单位是<tt class="docutils literal">ms</tt>)表示只有当耗时大于200ms时才会输出，过滤掉执行时间小于200ms的调用</li>
</ul>
</div>
<div class="section" id="">
<span id="id9"></span><h3>观察当前对象中的属性<a class="headerlink" href="#" title="永久链接至标题">¶</a></h3>
<p>如果想查看方法运行前后，当前对象中的属性，可以使用<tt class="docutils literal">target</tt>关键字，代表当前对象</p>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors 'target'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 52 ms.
ts=2018-12-03 19:41:52; [cost=0.477882ms] result=@MathGame[
random=@Random[java.util.Random@522b408a],
illegalArgumentCount=@Integer[13355],
]
</pre></div>
</div>
<p>然后使用<tt class="docutils literal">target.field_name</tt>访问当前对象的某个属性</p>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors 'target.illegalArgumentCount'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 67 ms.
ts=2018-12-03 20:04:34; [cost=131.303498ms] result=@Integer[8]
ts=2018-12-03 20:04:35; [cost=0.961441ms] result=@Integer[8]
</pre></div>
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