LOG4J Configuration Detailed

First, the use of log4j.properties detailed

1. Types of output levels

ERROR, WARN, INFO, DEBUG
Error is a critical error, mainly a program
WARN for general warnings, such as session loss
Info is the general information to display, such as login log out
Debug information for the program

2. Configure the log information output destination

Log4j.appender.appenderName = Fully.qualified.name.of.appender.class
1.org.apache.log4j.consoleappender (console)
2.org.apache.log4j.fileappender (file)
3.org.apache.log4j.dailyrollingfileappender (Generate a log file every day)
4.org.apache.log4j.rollingfileappender (creates a new file when the file size reaches the specified size)
5.org.apache.log4j.writerappender (send log information in stream format to any specified location)

3. Configure the format of log information

Log4j.appender.appenderName.layout = Fully.qualified.name.of.layout.class
1.org.apache.log4j.htmllayout (Layout in HTML table Form),
2.org.apache.log4j.patternlayout (flexibility to specify layout mode),
3.org.apache.log4j.simplelayout (contains the level of log information and the information string),
4.org.apache.log4j.ttcclayout (contains information about the time, thread, category, etc.) of the log

4. Console options

Threshold=debug: Specifies the lowest level of output for log messages.
Immediateflush=true: The default value is true, meaning that all messages will be output immediately.
Target=system.err: By default: System.out, specify output console
Fileappender Options
THRESHOLD=DEBUF: Specifies the lowest level of output for log messages.
Immediateflush=true: The default value is true, meaning that all messages will be output immediately.
File=mylog.txt: Specifies the message output to the Mylog.txt file.
Append=false: The default value is True, the message is added to the specified file, and false refers to overwriting the message with the specified file content.
Rollingfileappender Options
Threshold=debug: Specifies the lowest level of output for log messages.
Immediateflush=true: The default value is true, meaning that all messages will be output immediately.
File=mylog.txt: Specifies the message output to the Mylog.txt file.
Append=false: The default value is True, the message is added to the specified file, and false refers to overwriting the message with the specified file content.
MAXFILESIZE=100KB: The suffix can be kb, MB, or GB. When the log file reaches this size, it will automatically scroll to move the original content to the Mylog.log.1 file.
maxbackupindex=2: Specifies the maximum number of scroll files that can be produced.
log4j.appender.a1.layout.conversionpattern=%-4r%-5p%d{yyyy-mm-dd HH:mm:ssS}%c%m%n

5. The meaning of several symbols in the log Information format:

-X: Left-aligned when the information is output;
%p: Output log information priority, i.e. Debug,info,warn,error,fatal,
%d: the date or time of the output log time, the default format is ISO8601, can also be specified after the format, such as:%d{yyy MMM dd hh:mm:ss,sss}, output similar: October 18, 2002 22:10:28,921
%r: The number of milliseconds to output the log information from the application boot to output
%c: The class in which the output log information belongs, usually the full name of the class in which it is located
%t: Output The name of the thread that generated the log event
%l: The location of the output log event, which corresponds to the combination of%c.%m (%f:%l), including the class name, the thread that occurred, and the number of rows in the code. Example: Testlog4.main (testlog4.java:10)
%x: The NDC (nested diagnostic environment) associated with the output and current line threads, especially for multi-client multithreaded applications such as Java Servlets.
Percent: Output a "%" character
%F: The name of the file where the output log message was generated
%l: Line numbers in the output code
%M: The specified message in the output code, resulting in the log specific information
%n: Output a carriage return line break, Windows platform is "/r/n", UNIX Platform for "/n" output log information line-wrapping

You can add modifiers between% and pattern characters to control their minimum width, maximum width, and text alignment.

Such as:

1)%20c: Specify the name of the output category, the minimum width is 20, if the category name is less than 20, the default is the right alignment.
2)%-20c: Specify the name of the output category, the minimum width is 20, if the category name is less than 20, the "-" number specifies left-aligned.
3)%.30c: Specify the name of the output category, the maximum width is 30, if the category name is greater than 30, will be the left more than the character of the cut off, but less than 30, there will be no spaces.

4)%20.30c: If the category name is less than 20, fill in the blanks, and right-aligned, if its name is longer than 30 characters, it is truncated from the far left character.

Second, the configuration of log4j.properties

1. Configuration steps

1) using log4j in the application
2) put the Log4j-*.*jar into the CLASSPATH variable
3) Create a new profile log4j.properties, put it under the bin file

2. Create a new configuration file log4j.properties, such as:

Log4j.rootlogger=warn, stdout, R
Log4j.appender.stdout=org.apache.log4j.consoleappender
Log4j.appender.stdout.layout=org.apache.log4j.patternlayout
# Pattern to output the caller's file name and line number.
#log4j. appender.stdout.layout.conversionpattern=%5p [%t] (%f:%l)-%m%n
# Print the date in ISO 8601 format
log4j.appender.stdout.layout.conversionpattern=%d [%t]%-5p%c-%m%n
Log4j.appender.r=org.apache.log4j.rollingfileappender
Log4j.appender.r.file=example.log
log4j.appender.r.maxfilesize=100kb
# Keep One backup file
Log4j.appender.r.maxbackupindex=1
Log4j.appender.r.layout=org.apache.log4j.patternlayout
log4j.appender.r.layout.conversionpattern=%p%t%c-%m%n
# Print only messages of level WARN or above in the package Com.foo.
Log4j.logger.com.foo=warn

Compiling and running testlog4j will generate a Example.log file in the directory and the screen will output information, which proves that you have already succeeded in the first step.

Log4j Configuration Detailed