logback系列之二:输出日志到文件
logback系列之三:输出日志到文件(滚动)
logback系列之四:输出日志到不同文件
实际生产中,每天都有大量的日志生成,单个文件(FileAppender)已经不能满足要求,RollingFileAppender继承了FileAppender,并提供了更多的功能:
- 每天生成一个日志文件
- 将前一天的日志重命名为包含日期的格式
- 根据需要,删除过期历史日志
配置
和 logback系列之二:输出日志到文件类似,改动的地方:
1. logback[-test].xml文件:
<appender name="rollingAppender" class="ch.qos.logback.core.rolling.RollingFileAppender"> <file>/logs/heuristic.log</file> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <fileNamePattern>/logs/heuristic-%d{yyyy-MM-dd}.log</fileNamePattern> <maxHistory>30</maxHistory> </rollingPolicy> <encoder><!-- 必须指定,否则不会往文件输出内容 --> <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{5} - %msg%n</pattern> </encoder> <append>false</append> <prudent>false</prudent> </appender> <root level="DEBUG"> <appender-ref ref="rollingAppender" /> </root>
调用测试类的方法,生成heuristic-2013-11-16.log文件。
源码分析
a. 如果指定了file属性,当天的文件名为file属性值(/logs/heuristic.log):
ch.qos.logback.core.rolling.RollingFileAppender类
public void start() { ... currentlyActiveFile = new File(getFile()); // 获取日志文件名 } public String getFile() { return rollingPolicy.getActiveFileName(); // 从滚动策略获取 }
上面logback[-test].xml的rollingPolicy配置为
ch.qos.logback.core.rolling.TimeBasedRollingPolicy类
看下实现:
public String getActiveFileName() { String parentsRawFileProperty = getParentsRawFileProperty(); if (parentsRawFileProperty != null) { // logback.xml指定了file属性 return parentsRawFileProperty; // 使用file值 } else { return timeBasedFileNamingAndTriggeringPolicy .getCurrentPeriodsFileNameWithoutCompressionSuffix(); } } public String getParentsRawFileProperty() { return parent.rawFileProperty(); }
ch.qos.logback.core.FileAppender类
final public String rawFileProperty() { return fileName; }
b. 必须指定TriggeringPolicy<E>和RollingPolicy,否则不会打印日志:
看下
ch.qos.logback.core.rolling.RollingFileAppender类:
public void start() { if (triggeringPolicy == null) { addWarn("No TriggeringPolicy was set for the RollingFileAppender named " + getName()); addWarn("For more information, please visit "+CODES_URL+"#rfa_no_tp"); return; } if (rollingPolicy == null) { addError("No RollingPolicy was set for the RollingFileAppender named " + getName()); addError("For more information, please visit "+CODES_URL+"rfa_no_rp"); return; }
TimeBasedRollingPolicy类实现了上面的两个接口,triggeringPolicy和rollingPolicy都指向TimeBasedRollingPolicy的实例对象。
c. 如果file指定,前一天的文件名改为fileNamePattern的值(/logs/heuristic-2013-11-15.log)。
通过设置TimeBasedRollingPolicy的 maxHistory属性,可以控制已产生日志的数量。如果maxHistory设置为30,那么超过30天的log文件会被自动删除,这是通过RollingFileAppender的 rollover()方法来实现的。
该方法会调用
ch.qos.logback.core.rolling.TimeBasedRollingPolicy类
的rollover方法:
public void rollover() throws RolloverFailure { // 当此方法调用时,假定前一天日志文件已经关闭 String elapsedPeriodsFileName = timeBasedFileNamingAndTriggeringPolicy .getElapsedPeriodsFileName(); String elpasedPeriodStem = FileFilterUtil.afterLastSlash(elapsedPeriodsFileName); if (compressionMode == CompressionMode.NONE) { if (getParentsRawFileProperty() != null) { renameUtil.rename(getParentsRawFileProperty(), elapsedPeriodsFileName); // file指定,重命名为fileNamePattern格式。如果目标文件存在,则重命名失败 } // else { nothing to do if CompressionMode == NONE and parentsRawFileProperty == null } } else { if (getParentsRawFileProperty() == null) { future = asyncCompress(elapsedPeriodsFileName, elapsedPeriodsFileName, elpasedPeriodStem); // file未指定,异步压缩 } else { future = renamedRawAndAsyncCompress(elapsedPeriodsFileName, elpasedPeriodStem); // file指定,重命名并异步压缩 } } if (archiveRemover != null) { archiveRemover.clean(new Date(timeBasedFileNamingAndTriggeringPolicy.getCurrentTime())); // 删除历史日志 } }
默认的archiveRemover为 ch.qos.logback.core.rolling.helper.DefaultArchiveRemover抽象类:
public void clean(Date now) { long nowInMillis = now.getTime(); int periodsElapsed = computeElapsedPeriodsSinceLastClean(nowInMillis); lastHeartBeat = nowInMillis; if (periodsElapsed > 1) { addInfo("periodsElapsed = " + periodsElapsed); } // 从待删除日志的终止日期开始,每次回退一天,删除过期日志 for (int i = 0; i < periodsElapsed; i++) { cleanByPeriodOffset(now, periodOffsetForDeletionTarget - i); } } public void setMaxHistory(int maxHistory) { // 待删除日志的终止日期:回退(maxHistory+1)天 this.periodOffsetForDeletionTarget = -maxHistory - 1; }
cleanByPeriodOffset为抽象方法,这里交由
ch.qos.logback.core.rolling.helper.TimeBasedArchiveRemover子类实现:
protected void cleanByPeriodOffset(Date now, int periodOffset) { Date date2delete = rc.getRelativeDate(now, periodOffset); // 计算需要删除日志的日期 String filename = fileNamePattern.convert(date2delete); File file2Delete = new File(filename); if (file2Delete.exists() && file2Delete.isFile()) { file2Delete.delete(); // 删除文件 addInfo("deleting " + file2Delete); if (parentClean) { removeFolderIfEmpty(file2Delete.getParentFile()); } } }
d. 如果要启用压缩,需要将fileNamePattern的后缀名设置为压缩格式,如:/logs/heuristic-%d{yyyy-MM-dd}.zip。
看下 ch.qos.logback.core.rolling.RollingPolicyBase类相关的代码:
protected void determineCompressionMode() { if (fileNamePatternStr.endsWith(".gz")) { addInfo("Will use gz compression"); compressionMode = CompressionMode.GZ; } else if (fileNamePatternStr.endsWith(".zip")) { addInfo("Will use zip compression"); compressionMode = CompressionMode.ZIP; } else { // 如果后缀名不是.gz或.zip,不会启用压缩 addInfo("No compression will be used"); compressionMode = CompressionMode.NONE; } }
e. RollingFileAppender保证append的值为true,这样当天先写入的日志内容就不会丢失:
ch.qos.logback.core.rolling.RollingFileAppender类的start()方法:
if (!append) { // append为false时 addWarn("Append mode is mandatory for RollingFileAppender"); append = true; // 改成true }
f. prudent模式不支持file设定;如果启用了压缩,logback将不会记录日志:
ch.qos.logback.core.rolling.RollingFileAppender类
的start()方法:
if (isPrudent()) { // 安全模式,但效率低 if (rawFileProperty() != null) { addWarn("Setting \"File\" property to null on account of prudent mode"); setFile(null); // 取消file属性设置 } if (rollingPolicy.getCompressionMode() != CompressionMode.NONE) { // 启用了压缩 addError("Compression is not supported in prudent mode. Aborting"); return; // 返回,不会进行后面的记录日志操作 } }