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In this case, show how to dynamically modify the Logger Level.
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### Find the ClassLoader of the UserController
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`sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash`{{execute T2}}
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```bash
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$ sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash
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classLoaderHash 1be6f5c3
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```
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### Use ognl command to get the logger
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`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
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```bash
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$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
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@Logger[
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serialVersionUID=@Long[5454405123156820674],
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FQCN=@String[ch.qos.logback.classic.Logger],
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name=@String[com.example.demo.arthas.user.UserController],
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level=null,
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effectiveLevelInt=@Integer[20000],
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parent=@Logger[Logger[com.example.demo.arthas.user]],
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childrenList=null,
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aai=null,
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additive=@Boolean[true],
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loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
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]
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```
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可以知道`UserController@logger`实际使用的是logback。可以看到`level=null`，则说明实际最终的level是从`root` logger里来的。
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The user can know that `UserController@logger` actually uses logback. Because `level=null`, the actual final level is from the `root` logger.
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### Change the logger level of UserController
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`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger.setLevel(@ch.qos.logback.classic.Level@DEBUG)'`{{execute T2}}
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Get `UserController@logger` again, the user can see that it is already `DEBUG`:
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`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'`{{execute T2}}
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```bash
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$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'
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@Logger[
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serialVersionUID=@Long[5454405123156820674],
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FQCN=@String[ch.qos.logback.classic.Logger],
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name=@String[com.example.demo.arthas.user.UserController],
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level=@Level[DEBUG],
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effectiveLevelInt=@Integer[10000],
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parent=@Logger[Logger[com.example.demo.arthas.user]],
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childrenList=null,
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aai=null,
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additive=@Boolean[true],
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loggerContext=@LoggerContext[ch.qos.logback.classic.LoggerContext[default]],
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]
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```
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### Change the global logger level of the logback
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By getting the `root` logger, the user can modify the global logger level:
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`ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@org.slf4j.LoggerFactory@getLogger("root").setLevel(@ch.qos.logback.classic.Level@DEBUG)'`{{execute T2}}
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