Log4j

Apache Log4j is a versatile, industrial-grade Java logging framework composed of an API, its implementation, and components to assist the deployment for various use cases.

https://logging.apache.org/log4j/2.x/

• 控制日志信息输送的目的地是控制台、文件、GUI 组件，甚至是套接口服务器、NT 的事件记录器、UNIX Syslog 守护进程等
• 控制每一条日志的输出格式
• 通过定义每一条日志信息的级别，更加细致地控制日志的生成过程

ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF

pom.xml

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

log4j.properties

# log4j.rootLogger=CONSOLE,stdout,logfile
log4j.rootLogger=INFO,stdout
# log4j.rootLogger=Error,stdout
# Console
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%c]-%m%n

# File
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/system.log
log4j.appender.file.MaxFileSize=10mb
log4j.appender.file.Threshold=Error
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n

# Stdout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] %m%n

# Level
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

如 kafka 中会大量输入 debug 信息，可以指定输出级别或关闭(=OFF)：
log4j.logger.org.apache.kafka.clients=Error
log4j.logger.org.apache.kafka.common=Error
-.OR.-
log4j.logger.org.apache.kafka=Error

输出日志类

private static final Logger logger = Logger.getLogger(CLASSNAME.class)
...
logger.info("information...")

See Also

1. log4j详解及log4j.properties配置