Log

It is the process of writing log messages during the execution of a program to a central place.

Log Level

Usually the log level are as below, low -> high:

Debug
Info
Warn
Error
Fatal

Example

在下例中，在property文件里面定义了一个名为testlog的appender，并指定其级别为INFO，最后的输出是，除了Debug的其他行。

// log4j
import org.apache.log4j.Logger;
public class Main {
    static Logger log = Logger.getLogger("FILE");
    public static void main(String[] args) {
        log.debug("Debug");
        log.info("Info");
        log.warn("Warn");
        log.error("Error");
        log.fatal("Fatal");
    }
}

log4j.properties

# Define the root logger with appender file
log = C:/Some/Path/my.test.log
log4j.rootLogger = INFO, testlog

# Define the file appender
log4j.appender.testlog=org.apache.log4j.FileAppender
log4j.appender.testlog.File=${log}/log.out

# Define the layout for file appender
log4j.appender.testlog.layout=org.apache.log4j.PatternLayout
log4j.appender.testlog.layout.conversionPattern=%m%n

问题解决 - Log4j没有配置

Error: log4j:WARN No appenders could be found for logger

Fix：将log4j.perperties文件放到

src/

src/main/resources/
src/test/resources/

文件内容如下：直接输出log到控制台

log4j.rootLogger=info, stdout

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

log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=target/spring.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n

参考 -> log4j问题解决 https://blog.csdn.net/m0_37874657/article/details/80536086

Log

Log Level

Example

问题解决 - Log4j没有配置

Link