logback无法删除太久远的日志文件？logback删除日志文件源码分析

最近发现logback配置滚动日志，但是本地日志文件甚至还有2年前的日志文件，服务器是却是正常的！
网上搜索了一波没有发现，只找到说不能删除太久远的旧日志文件

我的配置

<!--    基于时间和空间的滚动日志，单个文件最大10MB，保留天数最大30天，所以日志保留最大空间是20GB    -->
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
    <fileNamePattern>/root/demo/logs/hornet_%d{yyyyMMdd}.%i.log</fileNamePattern>
    <maxFileSize>10mb</maxFileSize>
    <maxHistory>30</maxHistory>
    <totalSizeCap>20GB</totalSizeCap>
</rollingPolicy>

下面是源码分析

从配置可以看出，可以从 SizeAndTimeBasedRollingPolicy.class 着手

package ch.qos.logback.core.rolling;

import ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP.Usage;
import ch.qos.logback.core.util.FileSize;



public class SizeAndTimeBasedRollingPolicy<E> extends TimeBasedRollingPolicy<E> {

    FileSize maxFileSize;
    
    @Override
    public void start() {
        SizeAndTimeBasedFNATP<E> sizeAndTimeBasedFNATP = new SizeAndTimeBasedFNATP<E>(Usage.EMBEDDED); 
        if(maxFileSize == null) {
            addError("maxFileSize property is mandatory.");
            return;
        } else {
            addInfo("Archive files will be limited to ["+maxFileSize+"] each.");
        }
        
        sizeAndTimeBasedFNATP.setMaxFileSize(maxFileSize);
        timeBasedFileNamingAndTriggeringPolicy = sizeAndTimeBasedFNATP;
        
        if(!isUnboundedTotalSizeCap() && totalSizeCap.getSize() < maxFileSize.getSize()) {
            addError("totalSizeCap of ["+totalSizeCap+"] is smaller than maxFileSize ["+maxFileSize+"] which is non-sensical");
            return;
        }
        
        // most work is done by the parent
        super.start();
    }
    
    
    public void setMaxFileSize(FileSize aMaxFileSize) {
        this.maxFileSize = aMaxFileSize;
    }
    
    @Override
    public String toString() {
        return "c.q.l.core.rolling.SizeAndTimeBasedRollingPolicy@"+this.hashCode();
    }
}

这个类什么也没写，那逻辑肯定在父类 TimeBasedRollingPolicy.class

public void start() {
        // set the LR for our utility object
        renameUtil.setContext(this.context);

        // find out period from the filename pattern
        if (fileNamePatternStr != null) {
            fileNamePattern = new FileNamePattern(fileNamePatternStr, this.context);
            determineCompressionMode();
        } else {
            addWarn(FNP_NOT_SET);
            addWarn(CoreConstants.SEE_FNP_NOT_SET);
            throw new IllegalStateException(FNP_NOT_SET + CoreConstants.SEE_FNP_NOT_SET);
        }

        compressor = new Compressor(compressionMode);
        compressor.setContext(context);

        // wcs : without compression suffix
        fileNamePatternWithoutCompSuffix = new FileNamePattern(Compressor.computeFileNameStrWithoutCompSuffix(fileNamePatternStr, compressionMode), this.context);

        addInfo("Will use the pattern " + fileNamePatternWithoutCompSuffix + " for the active file");

        if (compressionMode == CompressionMode.ZIP) {
            String zipEntryFileNamePatternStr = transformFileNamePattern2ZipEntry(fileNamePatternStr);
            zipEntryFileNamePattern = new FileNamePattern(zipEntryFileNamePatternStr, context);
        }

        if (timeBasedFileNamingAndTriggeringPolicy == null) {
            timeBasedFileNamingAndTriggeringPolicy = new DefaultTimeBasedFileNamingAndTriggeringPolicy<E>();
        }
        timeBasedFileNamingAndTriggeringPolicy.setContext(context);
        timeBasedFileNamingAndTriggeringPolicy.setTimeBasedRollingPolicy(this);
        timeBasedFileNamingAndTriggeringPolicy.start();

        if (!timeBasedFileNamingAndTriggeringPolicy.isStarted()) {
            addWarn("Subcomponent did not start. TimeBasedRollingPolicy will not start.");
            return;
        }

		//*********** 可以看到这里有 maxHistory，也就是最大保留天数
		//*********** 可以看到这里有 maxHistory，也就是最大保留天数
		//*********** 可以看到这里有 maxHistory，也就是最大保留天数
		//*********** 大概意思就是判断是否初始化，然后把参数设置到archiveRemover中，
		//*********** 后面调用archiveRemover.cleanAsynchronously方法进行清理！！！				

        // the maxHistory property is given to TimeBasedRollingPolicy instead of to
        // the TimeBasedFileNamingAndTriggeringPolicy. This makes it more convenient
        // for the user at the cost of inconsistency here.
        if (maxHistory != UNBOUND_HISTORY) {
            archiveRemover = timeBasedFileNamingAndTriggeringPolicy.getArchiveRemover();
            archiveRemover.setMaxHistory(maxHistory);
            archiveRemover.setTotalSizeCap(totalSizeCap.getSize());
            if (cleanHistoryOnStart) {
                addInfo("Cleaning on start up");
                Date now = new Date(timeBasedFileNamingAndTriggeringPolicy.getCurrentTime());
                cleanUpFuture = archiveRemover.cleanAsynchronously(now);
            }
        } else if (!isUnboundedTotalSizeCap()) {
            addWarn("'maxHistory' is not set, ignoring 'totalSizeCap' option with value ["+totalSizeCap+"]");
        }

        super.start();
    }

进入 TimeBasedArchiveRemover.class,可以看到这是一个异步任务，重点在 clean()

    public Future<?> cleanAsynchronously(Date now) {
        ArhiveRemoverRunnable runnable = new ArhiveRemoverRunnable(now);
        ExecutorService executorService = context.getScheduledExecutorService();
        Future<?> future = executorService.submit(runnable);
        return future;
    }

    public class ArhiveRemoverRunnable implements Runnable {
        Date now;

        ArhiveRemoverRunnable(Date now) {
            this.now = now;
        }

        @Override
        public void run() {
            clean(now);
            if (totalSizeCap != UNBOUNDED_TOTAL_SIZE_CAP && totalSizeCap > 0) {
                capTotalSize(now);
            }
        }
    }

重点在 clean() ，清理，得到 periodsElapsed 天数，然后遍历清理 (-maxHistory+1)+i 天

    public void clean(Date now) {
 
        long nowInMillis = now.getTime();
        // for a live appender periodsElapsed is expected to be 1
        int periodsElapsed = computeElapsedPeriodsSinceLastClean(nowInMillis);
        lastHeartBeat = nowInMillis;
        if (periodsElapsed > 1) {
            addInfo("Multiple periods, i.e. " + periodsElapsed + " periods, seem to have elapsed. This is expected at application start.");
        }
        for (int i = 0; i < periodsElapsed; i++) {
            int offset = getPeriodOffsetForDeletionTarget() - i;
            Date dateOfPeriodToClean = rc.getEndOfNextNthPeriod(now, offset);
            cleanPeriod(dateOfPeriodToClean);
        }
    }

重要 computeElapsedPeriodsSinceLastClean() 计算 periodsElapsed 天数
UNINITIALIZED 先判断是否初始化
periodBarriersCrossed 计算过期出天数
INACTIVITY_TOLERANCE_IN_MILLIS 默认是32天（不知道为什么？？？）

    int computeElapsedPeriodsSinceLastClean(long nowInMillis) {
        long periodsElapsed = 0;
        if (lastHeartBeat == UNINITIALIZED) {
            addInfo("first clean up after appender initialization");
            periodsElapsed = rc.periodBarriersCrossed(nowInMillis, nowInMillis + INACTIVITY_TOLERANCE_IN_MILLIS);
            periodsElapsed = Math.min(periodsElapsed, MAX_VALUE_FOR_INACTIVITY_PERIODS);
        } else {
            periodsElapsed = rc.periodBarriersCrossed(lastHeartBeat, nowInMillis);
            // periodsElapsed of zero is possible for size and time based policies
        }
        return (int) periodsElapsed;
    }

所以得出结论：logback只能删除最近-maxHistory天到-maxHistory-32天的日志文件

补充：

logback默认不会在项目启动时清理旧日志文件，如果需要启动执行则需配置

<cleanHistoryOnStart>true</cleanHistoryOnStart>