Logger level and Output place

log4j Log Configuration
Keyword: Apache log4j
1. Configure Root logger:
Log4j.rootlogger = [level], Appendername, appenderName2
Levels: The level of the log that specifies the importance of this log information. is divided into all < DEBUG < INFO < WARN generally used for

DEBUG, INFO, WARN, error Four, four ways to correspond to logger class respectively
Debug (Object message);
Info (Object message);
Warn (Object message);
Error (Object message);
If the setting level is info, the log information with priority greater than or equal to the info level (such as: info, WARN, ERROR) will be output.

Less than this level, such as: Debug will not be output
Appendername: Specifies the log information output destination, such as (print to console, output to file, etc.). Same log information

Multiple output destinations can be configured.

2, configure log output destination:  
Org.apache.log4j.ConsoleAppender (console)  
Org.apache.log4j.FileAppender (file)  
Org.apache.log4j.DailyRollingFileAppender (produce one log file per day)  
Org.apache.log4j.RollingFileAppender (creates a new file when the file size reaches the specified size)  
Org.apache.log4j.WriterAppender (sends the log information in stream format to any specified place)  
3, format of log information:  
Org.apache.log4j.HTMLLayout (HTML table Form)  
Org.apache.log4j.SimpleLayout (a simple-format log that includes only the level of log information and the specified string of information, such as: D Ebug-hello)  
Org.apache.log4j.TTCCLayout (the format of the log includes information such as the time, thread, category, etc.)   the log was generated;
Org.apache.log4j.PatternLayout (Flexible custom log format)

When you use Org.apache.log4j.PatternLayout to customize the information format, you can use the
Log4j.appender.a1.layout.conversionpattern=%d{yyyy-mm-dd HH:mm:ss}%p-%m%n to format information
%c output belongs to the full name of the class, can be written as%c{num}, the Num class name output range such as: "Com.sun.aaa.classB",%c{2} will make the output range of the log output is: AAA.CLASSB
%d output log time in a format that can be specified in format such as%d{hh:mm:ss}
%l output Log event location, including the class name, the thread that occurred, the number of lines in the code
%n line break
%M Output code specifies information, such as info ("message"), output message
%p the priority of the output log, i.e. FATAL, ERROR, etc.
%r elapsed time (in milliseconds) from boot to display of this log information
%t output The name of the thread that generated the log event

4. Simultaneous use of commons-logging and log4j

1) First look for your own configuration file under Classpath commons-logging.properties, if found, use the

Log Implementation Class
2) If the Commons-logging.properties file is not found, find out if the system environment variable is defined

Org.apache.commons.logging.Log, find the Log implementation class that uses its definition
3) Otherwise, see if there are log4j packages in classpath, and if found, automatically use log4j as the log implementation class
4) Otherwise, use the JDK's own log implementation class (JDK1.4 only after the log implementation class)
5) Otherwise, use commons-logging to provide a simple log implementation class Simplelog

5. Multiple log files (Log4j.rootlogger=info, A1, A2)

#A2 output to a file rollingfileappender extension, you can provide a log backup function.

Log4j.appender.a2=org.apache.log4j.rollingfileappender
#日志文件的名称 Log4j.appender.a2.file=log4j.log
#日志文件的大小 log4j.appender.a2.maxfilesize=100kb
#保存一个备份文件 log4j.appender.a2.maxbackupindex=1

Log4j.appender.a2.layout=org.apache.log4j.ttcclayout

#log4j. Appender.a2.layout.conversionpattern=%-d{yyyy-mm-dd HH:mm:ss} [%c]-[%p]%m%n

By-Laws: (Log4j.properties)
Example 1:
Log4j.rootlogger=debug, stdout
Log4j.appender.stdout=org.apache.log4j.consoleappender
Log4j.appender.stdout.layout=org.apache.log4j.patternlayout
Log4j.appender.stdout.layout.conversionpattern=%c{1}-%m%n

Example 2:
#指定根Logger, and log output levels, logs greater than or equal to this level will be output (DEBUG < INFO < WARN < ERROR < FATAL) set to off to close the log
Log4j.rootlogger=debug, A1,A2
#指定log输出目的, this is set as the output log in the file My.Log of the specified directory
Log4j.appender.a1=org.apache.log4j.fileappender
Log4j.appender.a1.file=\\logs\\my.log #当前根目录下
#指定日志信息的格式
Log4j.appender.a1.layout=org.apache.log4j.patternlayout
Log4j.appender.a1.layout.conversionpattern=%r%d{yyyy-mm-dd HH:mm:ss}%c%p-%m%n

#把A2输出到控制台
Log4j.appender.a2=org.apache.log4j.consoleappender
Log4j.appender.a2.layout=org.apache.log4j.simplelayout

#还可以单独指定输出某个包的日志级别
#log4j. Logger.com.study.hellolog4j=info

Excerpt from: http://hi.baidu.com/zhangpeng0926/blog/item/a10dcdd8b1e9c42610df9b47.html