logback日志的删除策略

<!-- 日志文件输出 -->
<appender name="file" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <File>${log.base}/${log.moduleName}.log
    </File><!-- 设置日志不超过${log.max.size}时的保存路径，注意如果 是web项目会保存到Tomcat的bin目录 下 -->
    <!-- 滚动记录文件，先将日志记录到指定文件，当符合某个条件时，将日志记录到其他文件。-->
    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
        <FileNamePattern>${log.base}/archive/${log.moduleName}_all_%d{yyyy-MM-dd}.%i.log.zip
        </FileNamePattern>
        <!-- 当天的日志大小 超过${log.max.size}时,压缩日志并保存 -->
        <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
            <maxFileSize>${log.max.size}</maxFileSize>
        </timeBasedFileNamingAndTriggeringPolicy>
        <maxHistory>${log.max.history}</maxHistory>
    </rollingPolicy>
    <!-- 日志输出的文件的格式  -->
    <layout class="ch.qos.logback.classic.PatternLayout">
        <pattern>%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%thread]%logger{56}.%method\(\):%L -%msg%n</pattern>
    </layout>
</appender>

<timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
    <maxFileSize>${log.max.size}</maxFileSize>
</timeBasedFileNamingAndTriggeringPolicy>
<maxHistory>${log.max.history}</maxHistory>

if (maxHistory != INFINITE_HISTORY) {
  archiveRemover = timeBasedFileNamingAndTriggeringPolicy.getArchiveRemover();
  archiveRemover.setMaxHistory(maxHistory);
  if(cleanHistoryOnStart) {
    addInfo("Cleaning on start up");
    archiveRemover.clean(new Date(timeBasedFileNamingAndTriggeringPolicy.getCurrentTime()));
  }
}

int computeElapsedPeriodsSinceLastClean(long nowInMillis) {
    long periodsElapsed = 0;
    //如果尚未执行过清理操作，则默认清理除保留天数外64天以内的日志(由INACTIVITY_TOLERANCE_IN_MILLIS决定)
    if (lastHeartBeat == UNINITIALIZED) {
      addInfo("first clean up after appender initialization");
      periodsElapsed = rc.periodsElapsed(nowInMillis, nowInMillis + INACTIVITY_TOLERANCE_IN_MILLIS);
      if (periodsElapsed > MAX_VALUE_FOR_INACTIVITY_PERIODS)
        periodsElapsed = MAX_VALUE_FOR_INACTIVITY_PERIODS;
    } else {
      //如果已经执行过清理操作，则清理从上次到当前时间的需要清理的时间周期。
      periodsElapsed = rc.periodsElapsed(lastHeartBeat, nowInMillis);
      if (periodsElapsed < 1) {
        addWarn("Unexpected periodsElapsed value " + periodsElapsed);
        periodsElapsed = 1;
      }
    }
    return (int) periodsElapsed;
}

public void clean(Date now) {
    long nowInMillis = now.getTime();
    int periodsElapsed = computeElapsedPeriodsSinceLastClean(nowInMillis);
    lastHeartBeat = nowInMillis;
    if (periodsElapsed > 1) {
      addInfo("periodsElapsed = " + periodsElapsed);
    }
    //按天清理
    for (int i = 0; i < periodsElapsed; i++) {
      //periodOffsetForDeletionTarget=-maxHistory-1，如maxHistory为2，则该值为-3
      cleanByPeriodOffset(now, periodOffsetForDeletionTarget - i);
    }
}