How to use log4j package
LOG4J consists of three important components: the priority of log information, output destination of log information, and output format of log information. The priority of the log information is from high to Error, Warn, INFO, DEBUG, and is used to specify the importance of this log information. The output destination of log information specifies the log to print to the console or in the file; The format controls the display of log information.
Write profile
# Profile settingfilename.ini
Log4j.Rootlogger = Info, A1, A2
#setting for appender a1
Log4j.Appender.a1 = org.apache.log4j.consoleAppender
Log4j.Appender.a1.Layout = Org.apache.log4j.patternlayout
Log4j.Appender.a1.Layout.ConversionPattern =% - 4R% -5P [% T]% 37C% 3X -% M% N
#setting for appender a2
Log4j.appender. A2 = org.apache.log4j.rollingfileappender
Log4j.Appender. A2.File = example.log
Log4j.appender. A2.MaxFileSize = 100kb
Log4j.appender. A2.MaxBackupindex = 1
Log4j.Appender. A2.Layout = Org.apache.log4j.patternlayout
Log4j.Appender. A2.Layout.conversionPattern =% P% T% C -% M% N
Note: The log4j.appender must be lowercase
Note:
1. Configure root Logger, whose syntax is:
Log4j.rootlogger = [level], appendername, appendername, ...
Among them, Level is the priority of logging, divided into OFF, Fatal, Error, Warn, Info, Debug, All, or level you defined. Log4J is recommended to use only four levels, priority from high to low, Error, Warn, Info, Debug. By the level defined here, you can control the switch to the corresponding level of log information in the application. Specifying the output only shows information than this level, all information lower than this level will not be displayed. For example, the INFO level is defined here, and all the DEBUG level log information in the application will not be printed.
Appendername is where the specified log information is output to which place. You can specify multiple output destinations at the same time.
2. Configure the log information Output Destination Appender, its syntax is
Log4j.Appender.Appendername = flly.qualified.name.of.Appender.class
Log4j.appender.Appendername.Option1 = value1
...
Log4j.appender.Appendername.Option = VALUEN
Among them, the appender provided by Log4j has the following:
Org.apache.log4j.consoleappender (console),
Org.apache.log4j.fileappender (file),
Org.apache.log4j.dailyrollingFileAppender (a log file is generated),
Org.apache.log4j.rollingfileAppender Generate a new file when the specified size is specified, org.apache.log4j.writerappender (send log information to any specified place in stream format)
3. Configure the format (layout) of log information, whose syntax is:
Log4j.Appender.Appendername.Layout = Fully.qualified.Name.Of.Layout.class
Log4j.Appender.Appendername.Layout.Option1 = Value1
...
Log4j.Appender.Appendername.Layout.Option = VALUEN
Among them, Layout provided by LOG4J has the following:
Org.apache.log4j.htmlLayout (layout in HTML form),
Org.apache.log4j.patternlayout (you can flexibly designate the layout mode),
Org.apache.log4j.simplelayout (level and information string with log information),
Org.apache.log4j.ttccLayout (including information, thread, category, etc.)
4. When Layout is patternLayout, the format of ConversionPattern has the following options:
% R: Count the number of milliseconds consumed after the start
% T: A thread that represents a log record request
% P: Represents the priority of log statements
% R: Category Name related to log request
% C: The class name in the information
% M% N: Represents the content of the message
5. The configuration file also applies to the server side and the client.
Use of the code
1. Add the following lines in Import:
Import org.apache.log4j.propertyConfigurator;
Import org.apache.log4j.logger;
Import org.apache.log4j.level;
2. Define Logger variables
Static logger logger = logger.getlogger (ServerWithlog4j.class.getname ());
3. Read the configuration file
PropertyConfigurator.configure (String SettingFileName);
4. Display log information
Display log information by display level
Logger.debug (String log_info);
Used to display debugging information
Logger.info (String log_info);
Used to display system prompt information
Logger.warn (String log_info);
Used to display warnings or special tips
Logger.error (String log_info);
Used to display error information, generally used in an abnormality. E.g:
Catch (IOException E) {
Logger. Error ("IOException!");
System.exit (0);
}
The above is just a very simple use of the log4j package, if you encounter problems in use, check the API of the package to get more detailed information!
