arthas/tutorials/katacoda/case-ognl-update-logger-level-en/case-ognl-update-logger-level.md

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}}

$ sc -d com.example.demo.arthas.user.UserController | grep classLoaderHash
 classLoaderHash   1be6f5c3

Please write down your classLoaderHash here since it's dynamic. In the case here, it's 1be6f5c3.

if you use-c, you have to manually type hashcode by -c <hashcode>.

$ ognl -c 1be6f5c3 @com.example.demo.arthas.user.UserController@logger

For classloader with only one instance, it can be specified by --classLoaderClass using class name, which is more convenient to use.

$ ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader  @org.springframework.boot.SpringApplication@logger
@Slf4jLocationAwareLog[
    FQCN=@String[org.apache.commons.logging.LogAdapter$Slf4jLocationAwareLog],
    name=@String[org.springframework.boot.SpringApplication],
    logger=@Logger[Logger[org.springframework.boot.SpringApplication]],
]

The value of --classloaderclass is the class name of classloader. It can only work when it matches a unique classloader instance. The purpose is to facilitate the input of general commands. However, -c <hashcode> is dynamic.

Use ognl command to get the logger

ognl --classLoaderClass org.springframework.boot.loader.LaunchedURLClassLoader '@com.example.demo.arthas.user.UserController@logger'{{execute T2}}

$ 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}}

$ 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}}