Extended log4j supports the automatic deletion of log files according to time division and expired files

In order to meet our needs , Let's take a look at the original Log4j How to manage log files .

RollingFileAppender

• stay log4j in Appender Be responsible for writing the log to the log file , The service runs for a long time in the actual production environment , There will be many log files , So we usually use RollingFileAppender To cut the log according to the rules , Write to different log files .

• stay log4j The built-in class is org.apache.log4j.RollingFileAppender, The default function of this class is relatively simple , Through parameters maxBackupIndex To configure Rolling File The number of ,maxFileSize Configure the size of each log file , Then scroll through the output log .

• stay log4j:apache-log4j-extras:1.2.17 In this expansion package , A new class is re extended org.apache.log4j.rolling.RollingFileAppender. This RollingFileAppender You can check the file size or print the log according to different parameters Rolling File, But this, this Appender The function of deleting log files is lost （ No at all maxBackupIndex Parameters …）.

TriggeringPolicy

• org.apache.log4j.rolling.RollingFileAppender in TriggeringPolicy To indicate progress Rolling Log File The strategy of . The official offers two org.apache.log4j.rolling.SizeBasedTriggeringPolicy and org.apache.log4j.rolling.TimeBasedRollingPolicy Two strategies are implemented , Users can also expand new Policy.

TriggeringPolicy.isTriggeringEvent()

• When TriggeringPolicy.isTriggeringEvent() The method is judged as true when , Conduct Rolling File operation ;
• o.g.l.r.SizeBasedTriggeringPolicy Medium isTriggeringEvent() The judgment condition of is that the log file size is greater than maxFileSize.
• o.g.l.r.TimeBasedRollingPolicy Medium isTriggeringEvent() It is based on the system time and FileNamePattern Parameters to calculate Rolling File The name of the file , When Rolling File The file name of has changed , Conduct Rolling File operation ;

rollover

• When TriggeringPolicy Of isTriggeringEvent() Method returns True after ,o.a.l.rolling.RollingFileAppender Start execution rollover() Method
• rollover() Method wait for the last rollover End of normal execution
• adopt policy Of rollingPolicy.rollover(getFile()) Method , return RolloverDescription object , Express Rolling File A series of actions .
• Synchronous execution RolloverDescription Medium Synchronous Action operation （ For example, rename the file ） And wait for success .
• Start asynchronous thread , perform RolloverDescription Medium Asynchronous Action operation （ For example, compress log files ）.
• Action The concept of can be a single task operation , It can also be a group of task operations （CompositeAction）

summary

about Long Running Of Java process , We need more than Rolling File The operation of , We also need to understand history Log File Clean up . So I referred to TimeBasedRollingPolicy Code , Realized ExtendedTimeBasedRollingPolicy class . In the original class ,asynchronous It's alone compressAction Be responsible for compressing log files （ When conditions are met ）, Let's replace this object with CompositeAction, Then add the one we want to be responsible for cleaning up the files PurgeExpiredLogsAction that will do . stay PurgeExpiredLogsAction in , We can flexibly use the file name of the log , Number of log files , File size and other conditions , Delete the historical log file .