<liclass="toctree-l2"><aclass="reference internal"href="#how-much-impact-does-arthas-attach-have-on-the-performance-of-the-original-process">How much impact does Arthas attach have on the performance of the original process?</a></li>
<liclass="toctree-l2"><aclass="reference internal"href="#can-commands-such-as-trace-watch-enhance-the-classes-in-jdk">Can commands such as trace/watch enhance the classes in jdk?</a></li>
<liclass="toctree-l2"><aclass="reference internal"href="#how-to-view-the-result-in-json-format">How to view the result in <codeclass="docutils literal notranslate"><spanclass="pre">json</span></code> format</a></li>
<liclass="toctree-l2"><aclass="reference internal"href="#can-arthas-view-the-value-of-a-variable-in-memory">Can arthas view the value of a variable in memory?</a></li>
<liclass="toctree-l1"><aclass="reference external"href="https://github.com/alibaba/arthas">Star me at GitHub</a></li>
<liclass="toctree-l1"><aclass="reference external"href="https://github.com/alibaba/arthas/blob/master/CONTRIBUTING.md#">Compile and debug/CONTRIBUTING</a></li>
<h1>FAQ<aclass="headerlink"href="#faq"title="Permalink to this headline">¶</a></h1>
<blockquote>
<div><p>For questions that are not in this list, please search in issues. <aclass="reference external"href="https://github.com/alibaba/arthas/issues">https://github.com/alibaba/arthas/issues</a></p>
<h2>How much impact does Arthas attach have on the performance of the original process?<aclass="headerlink"href="#how-much-impact-does-arthas-attach-have-on-the-performance-of-the-original-process"title="Permalink to this headline">¶</a></h2>
<h2>Can commands such as trace/watch enhance the classes in jdk?<aclass="headerlink"href="#can-commands-such-as-trace-watch-enhance-the-classes-in-jdk"title="Permalink to this headline">¶</a></h2>
<p>By default, classes beginning with <codeclass="docutils literal notranslate"><spanclass="pre">java.</span></code> are filtered out, but they can be turned on:</p>
<h2>How to view the result in <codeclass="docutils literal notranslate"><spanclass="pre">json</span></code> format<aclass="headerlink"href="#how-to-view-the-result-in-json-format"title="Permalink to this headline">¶</a></h2>
<h2>Can arthas view the value of a variable in memory?<aclass="headerlink"href="#can-arthas-view-the-value-of-a-variable-in-memory"title="Permalink to this headline">¶</a></h2>
<p>No. But you can use some tricks to intercept the object with the <codeclass="docutils literal notranslate"><spanclass="pre">tt</span></code> command, or fetch it from a static method.</p>
<h2>How to filter method with the same name?<aclass="headerlink"href="#how-to-filter-method-with-the-same-name"title="Permalink to this headline">¶</a></h2>
<p>You can used all variables in <aclass="reference internal"href="advice-class.html"><spanclass="doc">fundamental fields in expressions</span></a> for the condition express to filter method with the same name, you can use the number of parameters <codeclass="docutils literal notranslate"><spanclass="pre">params.length</span><spanclass="pre">==1</span></code>,parameter type <codeclass="docutils literal notranslate"><spanclass="pre">params[0]</span><spanclass="pre">instanceof</span><spanclass="pre">java.lang.Integer</span></code>,return value type <codeclass="docutils literal notranslate"><spanclass="pre">returnObj</span><spanclass="pre">instanceof</span><spanclass="pre">java.util.List</span></code> and so on in one or more combinations as condition express.</p>
<p>You can use <codeclass="docutils literal notranslate"><spanclass="pre">-v</span></code> to view the condition express result <aclass="reference external"href="https://github.com/alibaba/arthas/issues/1348">https://github.com/alibaba/arthas/issues/1348</a></p>
<h2>java.lang.ClassFormatError: null, skywalking arthas compatible use<aclass="headerlink"href="#java-lang-classformaterror-null-skywalking-arthas-compatible-use"title="Permalink to this headline">¶</a></h2>
<p>When error log appear <codeclass="docutils literal notranslate"><spanclass="pre">java.lang.ClassFormatError:</span><spanclass="pre">null</span></code>, it is usually modified by other bytecode tools that are not compatible with arthas modified bytecode.</p>
<p>For example: use skywalking V8.1.0 below <aclass="reference external"href="https://github.com/alibaba/arthas/issues/1141">cannot trace, watch classes enhanced by skywalking agent</a>, V8.1.0 or above is compatible, refer to skywalking configuration for more details. <aclass="reference external"href="https://github.com/apache/skywalking/blob/v8.1.0/docs/en/FAQ/Compatible-with-other-javaagent-bytecode-processing">skywalking compatible with other javaagent bytecode processing</a>.</p>
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