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> dump 已加载类的 bytecode 到特定目录
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### 参数说明
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|参数名称|参数说明|
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|---:|:---|
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|*class-pattern*|类名表达式匹配|
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|`[c:]`|类所属 ClassLoader 的 hashcode|
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|`[d:]`|设置类文件的目标目录|
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|`[classLoaderClass:]`|指定执行表达式的 ClassLoader 的 class name|
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|[E]|开启正则表达式匹配，默认为通配符匹配|
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### 使用参考
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`dump java.lang.String`{{execute T2}}
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```bash
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$ dump java.lang.String
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HASHCODE CLASSLOADER LOCATION
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null /Users/admin/logs/arthas/classdump/java/lang/String.class
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Affect(row-cnt:1) cost in 119 ms.
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```
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`dump demo.*`{{execute T2}}
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```bash
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$ dump demo.*
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HASHCODE CLASSLOADER LOCATION
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3d4eac69 +-sun.misc.Launcher$AppClassLoader@3d4eac69 /Users/admin/logs/arthas/classdump/sun.misc.Launcher$AppClassLoader-3d4eac69/demo/MathGame.class
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+-sun.misc.Launcher$ExtClassLoader@66350f69
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Affect(row-cnt:1) cost in 39 ms.
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```
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`dump -d /tmp/output java.lang.String`{{execute T2}}
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```bash
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$ dump -d /tmp/output java.lang.String
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HASHCODE CLASSLOADER LOCATION
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null /tmp/output/java/lang/String.class
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Affect(row-cnt:1) cost in 138 ms.
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```
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* 指定classLoader
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注意hashcode是变化的，需要先查看当前的ClassLoader信息，提取对应ClassLoader的hashcode。
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如果你使用`-c`，你需要手动输入hashcode：`-c <hashcode>`
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```bash
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$ dump -c 3d4eac69 demo.*
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```
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对于只有唯一实例的ClassLoader可以通过`--classLoaderClass`指定class name，使用起来更加方便：
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`dump --classLoaderClass sun.misc.Launcher$AppClassLoader demo.*`{{execute T2}}
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```bash
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$ dump --classLoaderClass sun.misc.Launcher$AppClassLoader demo.*
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HASHCODE CLASSLOADER LOCATION
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3d4eac69 +-sun.misc.Launcher$AppClassLoader@3d4eac69 /Users/admin/logs/arthas/classdump/sun.misc.Launcher$AppClassLoader-3d4eac69/demo/MathGame.class
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+-sun.misc.Launcher$ExtClassLoader@66350f69
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Affect(row-cnt:1) cost in 39 ms.
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```
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* 注: 这里classLoaderClass 在 java 8 是 sun.misc.Launcher$AppClassLoader，而java 11的classloader是jdk.internal.loader.ClassLoaders$AppClassLoader，katacoda目前环境是java8。
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`--classLoaderClass` 的值是ClassLoader的类名，只有匹配到唯一的ClassLoader实例时才能工作，目的是方便输入通用命令，而`-c <hashcode>`是动态变化的。
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