DailyRollingFileAppender

DailyRollingFileAppender is a component in Apache Log4j 1.x that writes log events to a file and rotates the file at a fixed time interval, typically daily. When a rollover occurs, the current log file is closed and renamed by appending a date pattern to its name, and a new log file is opened for subsequent logging. The rotation period is determined by the DatePattern property; for example, a DatePattern of '.'yyyy-MM-dd will produce a separate file for each day, with the date suffix appended to the base file name specified by the File property.

Configuration of DailyRollingFileAppender is done in the Log4j configuration file. A typical setup in a properties file looks like:

log4j.appender.DAILY=org.apache.log4j.DailyRollingFileAppender

log4j.appender.DAILY.File=logs/app.log

log4j.appender.DAILY.DatePattern='.'yyyy-MM-dd

log4j.appender.DAILY.Layout=org.apache.log4j.PatternLayout

log4j.appender.DAILY.Layout.ConversionPattern=%d %-5p %c - %m%n

Key characteristics and limitations:

- Rotation is time-based, producing separate files for each period (e.g., day, hour) depending on the DatePattern.

- It does not provide built-in compression or automatic deletion/retention of old files; managing old logs usually requires external scripts or manual cleanup.

- It is not well-suited for multi-process scenarios where multiple JVMs write to the same file, as concurrent access can cause conflicts.

- Log4j 1.x, including DailyRollingFileAppender, is end-of-life; for new projects, it is recommended to migrate to Log4j 2.x, which uses a RollingFileAppender with a TimeBasedTriggeringPolicy and a more flexible retention strategy.

In modern usage, DailyRollingFileAppender is largely superseded by the more configurable rolling appenders in Log4j 2.x or alternatives in other logging frameworks.

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