A closer look at log4j configuration: setting the logger's level and output target

Detailed explanation of log4j configuration: Logger level and output target settings require specific code examples

Introduction:
In the software development process, logging is A very important job. It not only helps developers quickly locate problems during the debugging phase, but also helps operation and maintenance personnel track and analyze the running status of the system in the production environment. As a powerful Java logging component, log4j can meet our various needs for logging.

This article will explain the configuration of log4j in detail, including the logger level and output target settings, and attach specific code examples.

1. Logger level settings
log4j defines 7 levels of loggers, which in order from low to high are: TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF. Through configuration, we can set the minimum level to be logged, and logs higher than this level will not be logged.

In the log4j configuration file (usually log4j.properties or log4j.xml), you can configure the level of the logger by setting the following parameters:

log4j.rootLogger=级别, 输出目标

Among them, the level can be the above 7 one of the levels, or a custom level. The output target can be console output (ConsoleAppender), file output (FileAppender), database output (JDBCAppender), etc.

For example, we set the logger level to DEBUG, that is, only logs with DEBUG level and above are recorded:

log4j.rootLogger=DEBUG, ConsoleAppender

2. Output target settings
In addition to setting the logger In addition to levels, log4j also allows us to output logs to different targets, so that we can choose to output logs to consoles, files, databases, etc. as needed.

1. Output to console
   Outputting logs to the console is very simple. We only need to configure a ConsoleAppender and then add it to the rootLogger. The following is a relevant code example:

log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%d [%t] %p %c - %m%n

log4j.rootLogger=DEBUG, console

2. Output to file
   Outputting the log to a file is also very easy, we only need to configure a FileAppender and then add it to the rootLogger. The following is a relevant code example:

log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=/path/to/log/file.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d [%t] %p %c - %m%n

log4j.rootLogger=DEBUG, file

It should be noted that "/path/to/log/file.log" in the above code needs to be replaced with the actual file path.

3. Output to database
   To output logs to the database, you need to use JDBCAppender. We need to provide relevant database connection information and log table structure. The following is a relevant code example:

log4j.appender.db=org.apache.log4j.jdbc.JDBCAppender
log4j.appender.db.URL=jdbc:mysql://localhost:3306/log_db
log4j.appender.db.driver=com.mysql.jdbc.Driver
log4j.appender.db.user=root
log4j.appender.db.password=password

log4j.appender.db.sql=INSERT INTO logs(datetime, thread, level, logger, message) VALUES('%d{yyyy-MM-dd HH:mm:ss}', '%t', '%p', '%c', '%m')

log4j.rootLogger=DEBUG, db

It should be noted that "log_db" in the above code needs to be replaced with the actual database name.

Conclusion:
log4j is a powerful and easy-to-use Java logging component. It provides a wealth of configuration options to meet our various needs for logging. Through the introduction and code examples of this article, I believe readers can better understand and use the configuration function of log4j, and can flexibly apply it in actual development. Hope this article is helpful to everyone!

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