vcjmhg edited a comment on issue #4545:
URL: https://github.com/apache/skywalking/issues/4545#issuecomment-729419758
# Summary
The plug-in can store the logs generated by the program during the call,
such as the content of the error log, into the span log. And the plug-in
provides matching files. Through the configuration file, you can control the
log source (log4j2, logbak, log4j), package name, level, and content that need
to be stored in the span log, and you can customize the log format saved to the
span log. .
# Configuration file
`logfilter.yaml`
```yaml
- name: "log4j2"
packages:
- package1
- package2
level: "trace"
pattern: "%date %level [%thread] %logger{10} [%file:%line] %msg%n"
expression: "Regular expression"
- name: "logbak"
packages:
- package3
level: "error"
patterns: "%msg%n"
expression: "Regular expression"
```
# Field description
**name attribute**: Specify the log system that needs to perform log
conversion. If you use a configuration file for configuration, the name must be
written.
There are four values for name:
* log4j
* log4j2
* logbak
* `*`:Match all supported log
**package attribute**: Specify the package name of the log that needs log
conversion. When using the configuration file for configuration, it can be
defaulted. If the default is stupid with `*`, it will match all packages.
`package value`:
* the name of package, eg: `org.apache.skywalking`
* `*`:match all
**level attribute**: The level of the log for conversion. **By default it is
`error` level**
* trace
* debug
* info
* error
**pattern attribute:** used to control the format of the log written to the
span log
The control method of the specific format, refer to logbak, for details,
please refer to http://logback.qos.ch/manual/layouts.html
**expression attribute**: filter logs that need to be converted into lspan
log. This attribute accepts a regular expression, the content of the log body
will be matched, if it is matched, then input, otherwise no conversion will be
performed. **By default, it matches all, that is, no filtering is performed. **
# Realization idea
1. Analyze the configuration file and fill it into a instance of
`loggerConfig`, which contains a List to store Logger, which is a record of
configuration information of the logging system.
2. After the error method is intercepted, the log level will be determined
according to the configuration file. **If the level requirements are met**, the
regular expression filtering will begin. If the filtering requirements are met,
the instance of `LogEvent` will be created. After filling, execute the formate
method to format the log information.
**Formatting operation method (modeled on PatternLayout to realize log
analysis):**
1. The `LoggerFactory.getLogger()` method is enhanced to obtain the
logger object. And then get the object of `LoggerContext` .
```java
Logger logger = LoggerFactory.getLogger(CaseController.class);
ch.qos.logback.classic.Logger myLogger =
(ch.qos.logback.classic.Logger) logger;
LoggerContext context = myLogger.getLoggerContext();
```
2. Rewrite a suitable Appender or use `PatternLayoutEncorder` directly to
format the required information
```java
Logger rootLogger =
(Logger)LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
LoggerContext loggerContext = rootLogger.getLoggerContext();
// we are not interested in auto-configuration
loggerContext.reset();
PatternLayoutEncoder encoder = new PatternLayoutEncoder();
encoder.setContext(loggerContext);
encoder.setPattern("%-5level [%thread]: %message%n");
encoder.start();
ConsoleAppender<ILoggingEvent> appender = new
ConsoleAppender<ILoggingEvent>();
appender.setContext(loggerContext);
appender.setEncoder(encoder);
appender.start();
rootLogger.addAppender(appender);
rootLogger.debug("Message 1");
rootLogger.warn("Message 2");
```
3. After the operation is completed, initialize the instance of
`ContextCarrier` to obtain the span and then place the corresponding
information in the `spanlog`
4. Stop `sapn`
# Some problems
1. `LogbakLoggerFactoryInstrumentation` is not working well and I can't get
the the instance of `org.slf4j.LoggerFactory`.Now I am fixing it.
2. The function of formatting the log has not been fully completed yet.
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