Print the logger information, update the logger level
### Usage
#### Print the logger information
`logger` {{execute T2}}
```bash
[arthas@2062]$ logger
name ROOT
class ch.qos.logback.classic.Logger
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
level INFO
effectiveLevel INFO
additivity true
codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
appenders name CONSOLE
class ch.qos.logback.core.ConsoleAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
target System.out
name APPLICATION
class ch.qos.logback.core.rolling.RollingFileAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
file app.log
name ASYNC
class ch.qos.logback.classic.AsyncAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
appenderRef [APPLICATION]
```
#### View logger information for the special name
`logger -n org.springframework.web` {{execute T2}}
```bash
[arthas@2062]$ logger -n org.springframework.web
name org.springframework.web
class ch.qos.logback.classic.Logger
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
level null
effectiveLevel INFO
additivity true
codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
```
Please write down your classLoaderHash here, in the case here, it's `2a139a55` . It will be used in the future steps.
Note: Please replace `<classLoaderHash>` with your classLoaderHash above, then execute the commands manually in the following steps:
#### View logger information for the special classloader
Note that the hashcode changes, you need to check the current ClassLoader information first, and extract the hashcode corresponding to the ClassLoader.
if you use`-c`, you have to manually type hashcode by `-c <hashcode>` .
```bash
$ logger -c 2a139a55
```
For classloader with only one instance, it can be specified by `--classLoaderClass` using class name, which is more convenient to use.
`logger --classLoaderClass sun.misc.Launcher$AppClassLoader` {{execute T2}}
```bash
[arthas@2062]$ logger --classLoaderClass sun.misc.Launcher$AppClassLoader
name ROOT
class ch.qos.logback.classic.Logger
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
level DEBUG
effectiveLevel DEBUG
additivity true
codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
appenders name CONSOLE
class ch.qos.logback.core.ConsoleAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
target System.out
name APPLICATION
class ch.qos.logback.core.rolling.RollingFileAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
file app.log
name ASYNC
class ch.qos.logback.classic.AsyncAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
appenderRef [APPLICATION]
```
* PS: Here the classLoaderClass in java 8 is sun.misc.Launcher$AppClassLoader, while in java 11 it's jdk.internal.loader.ClassLoaders$AppClassLoader. Currently katacoda using java 8.
The value of `--classloaderclass` is the class name of classloader. It can only work when it matches a unique classloader instance. The purpose is to facilitate the input of general commands. However, `-c <hashcode>` is dynamic.
#### Update logger level
`logger --name ROOT --level debug` {{execute T2}}
```bash
[arthas@2062]$ logger --name ROOT --level debug
update logger level success.
```
#### 指定classloader更新 logger level
默认情况下， ， ， ，
可以先用 `sc -d yourClassName` 来查看具体的 classloader hashcode， ：
`logger --classLoaderClass sun.misc.Launcher$AppClassLoader --name ROOT --level debug` {{execute T2}}
```bash
[arthas@2062]$ logger --classLoaderClass sun.misc.Launcher$AppClassLoader --name ROOT --level debug
```
#### View the logger information without appenders
By default, the `logger` command only prints information about the logger with appenders. If you want to see information about loggers without `appender` , you can use the parameter `--include-no-appender` .
Note that the output will usually be very long.
`logger --include-no-appender` {{execute T2}}
```bash
[arthas@2062]$ logger --include-no-appender
name ROOT
class ch.qos.logback.classic.Logger
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
level DEBUG
effectiveLevel DEBUG
additivity true
codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
appenders name CONSOLE
class ch.qos.logback.core.ConsoleAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
target System.out
name APPLICATION
class ch.qos.logback.core.rolling.RollingFileAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
file app.log
name ASYNC
class ch.qos.logback.classic.AsyncAppender
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
appenderRef [APPLICATION]
name com
class ch.qos.logback.classic.Logger
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
level null
effectiveLevel DEBUG
additivity true
codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
name com.alibaba
class ch.qos.logback.classic.Logger
classLoader sun.misc.Launcher$AppClassLoader@2a139a55
classLoaderHash 2a139a55
level null
effectiveLevel DEBUG
additivity true
codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
...
```
