arthas/tutorials/katacoda/command-ognl-en/case-ognl-update-logger-level.md
2020-08-08 00:22:24 +08:00

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