聊聊logback的FixedWindowRollingPolicy

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本文主要研究一下logback的FixedWindowRollingPolicy

RollingPolicy

ch/qos/logback/core/rolling/RollingPolicy.java

/*** A <code>RollingPolicy</code> is responsible for performing the rolling over* of the active log file. The <code>RollingPolicy</code> is also responsible* for providing the <em>active log file</em>, that is the live file where* logging output will be directed.* * @author Ceki G&uuml;lc&uuml;*/
public interface RollingPolicy extends LifeCycle {/*** Rolls over log files according to implementation policy.* * <p>* This method is invoked by {@link RollingFileAppender}, usually at the behest* of its {@link TriggeringPolicy}.* * @throws RolloverFailure Thrown if the rollover operation fails for any*                         reason.*/void rollover() throws RolloverFailure;/*** Get the name of the active log file.* * <p>* With implementations such as {@link TimeBasedRollingPolicy}, this method* returns a new file name, where the actual output will be sent.* * <p>* On other implementations, this method might return the FileAppender's file* property.*/String getActiveFileName();/*** The compression mode for this policy.* * @return*/CompressionMode getCompressionMode();/*** This method allows RollingPolicy implementations to be aware of their* containing appender.* * @param appender*/void setParent(FileAppender<?> appender);
}

RollingPolicy接口定义了rollover、getActiveFileName、getCompressionMode、setParent方法

RollingPolicyBase

ch/qos/logback/core/rolling/RollingPolicyBase.java

/*** Implements methods common to most, it not all, rolling policies. Currently* such methods are limited to a compression mode getter/setter.* * @author Ceki Gülcü*/
public abstract class RollingPolicyBase extends ContextAwareBase implements RollingPolicy {protected CompressionMode compressionMode = CompressionMode.NONE;FileNamePattern fileNamePattern;// fileNamePatternStr is always slashified, see setterprotected String fileNamePatternStr;private FileAppender<?> parent;// use to name files within zip file, i.e. the zipEntryFileNamePattern zipEntryFileNamePattern;private boolean started;/*** Given the FileNamePattern string, this method determines the compression mode* depending on last letters of the fileNamePatternStr. Patterns ending with .gz* imply GZIP compression, endings with '.zip' imply ZIP compression. Otherwise* and by default, there is no compression.* */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 {addInfo("No compression will be used");compressionMode = CompressionMode.NONE;}}//......
}    

RollingPolicyBase定义了compressionMode、fileNamePattern、fileNamePatternStr、parent、zipEntryFileNamePattern、started；
determineCompressionMode方法会根据fileNamePatternStr的后缀来判断，默认支持gz、zip

FixedWindowRollingPolicy

ch/qos/logback/core/rolling/FixedWindowRollingPolicy.java

public class FixedWindowRollingPolicy extends RollingPolicyBase {static final String FNP_NOT_SET = "The \"FileNamePattern\" property must be set before using FixedWindowRollingPolicy. ";static final String PRUDENT_MODE_UNSUPPORTED = "See also " + CODES_URL + "#tbr_fnp_prudent_unsupported";static final String SEE_PARENT_FN_NOT_SET = "Please refer to " + CODES_URL + "#fwrp_parentFileName_not_set";int maxIndex;int minIndex;RenameUtil util = new RenameUtil();Compressor compressor;public static final String ZIP_ENTRY_DATE_PATTERN = "yyyy-MM-dd_HHmm";/*** It's almost always a bad idea to have a large window size, say over 20.*/private static int MAX_WINDOW_SIZE = 20;public FixedWindowRollingPolicy() {minIndex = 1;maxIndex = 7;}//......
}    

FixedWindowRollingPolicy继承了RollingPolicyBase，他定义了minIndex、maxIndex、compressor属性

start

    public void start() {util.setContext(this.context);if (fileNamePatternStr != null) {fileNamePattern = new FileNamePattern(fileNamePatternStr, this.context);determineCompressionMode();} else {addError(FNP_NOT_SET);addError(CoreConstants.SEE_FNP_NOT_SET);throw new IllegalStateException(FNP_NOT_SET + CoreConstants.SEE_FNP_NOT_SET);}if (isParentPrudent()) {addError("Prudent mode is not supported with FixedWindowRollingPolicy.");addError(PRUDENT_MODE_UNSUPPORTED);throw new IllegalStateException("Prudent mode is not supported.");}if (getParentsRawFileProperty() == null) {addError("The File name property must be set before using this rolling policy.");addError(SEE_PARENT_FN_NOT_SET);throw new IllegalStateException("The \"File\" option must be set.");}if (maxIndex < minIndex) {addWarn("MaxIndex (" + maxIndex + ") cannot be smaller than MinIndex (" + minIndex + ").");addWarn("Setting maxIndex to equal minIndex.");maxIndex = minIndex;}final int maxWindowSize = getMaxWindowSize();if ((maxIndex - minIndex) > maxWindowSize) {addWarn("Large window sizes are not allowed.");maxIndex = minIndex + maxWindowSize;addWarn("MaxIndex reduced to " + maxIndex);}IntegerTokenConverter itc = fileNamePattern.getIntegerTokenConverter();if (itc == null) {throw new IllegalStateException("FileNamePattern [" + fileNamePattern.getPattern() + "] does not contain a valid IntegerToken");}if (compressionMode == CompressionMode.ZIP) {String zipEntryFileNamePatternStr = transformFileNamePatternFromInt2Date(fileNamePatternStr);zipEntryFileNamePattern = new FileNamePattern(zipEntryFileNamePatternStr, context);}compressor = new Compressor(compressionMode);compressor.setContext(this.context);super.start();}

start方法先根据fileNamePattern来创建FileNamePattern，然后判断压缩模式，然后校验minIndex及maxIndex，要求相差不能超过MAX_WINDOW_SIZE(默认值为20)，之后判断如果是zip模式的则创建zipEntryFileNamePattern，最后根据压缩模式创建compressor

rollover

    public void rollover() throws RolloverFailure {// Inside this method it is guaranteed that the hereto active log file is// closed.// If maxIndex <= 0, then there is no file renaming to be done.if (maxIndex >= 0) {// Delete the oldest file, to keep Windows happy.File file = new File(fileNamePattern.convertInt(maxIndex));if (file.exists()) {file.delete();}// Map {(maxIndex - 1), ..., minIndex} to {maxIndex, ..., minIndex+1}for (int i = maxIndex - 1; i >= minIndex; i--) {String toRenameStr = fileNamePattern.convertInt(i);File toRename = new File(toRenameStr);// no point in trying to rename a nonexistent fileif (toRename.exists()) {util.rename(toRenameStr, fileNamePattern.convertInt(i + 1));} else {addInfo("Skipping roll-over for inexistent file " + toRenameStr);}}// move active file name to minswitch (compressionMode) {case NONE:util.rename(getActiveFileName(), fileNamePattern.convertInt(minIndex));break;case GZ:compressor.compress(getActiveFileName(), fileNamePattern.convertInt(minIndex), null);break;case ZIP:compressor.compress(getActiveFileName(), fileNamePattern.convertInt(minIndex),zipEntryFileNamePattern.convert(new Date()));break;}}}

rollover方法从maxIndex-1开始到minIndex，把这些文件名的序号加1，之后根据压缩模式判断，如果不压缩则把当前文件名重名为minIndex，若是gz压缩则把当前文件压缩然后命名为minIndex，若是zip压缩则把当前文件压缩然后命名为minIndex加上日期

小结

logback的FixedWindowRollingPolicy继承了RollingPolicyBase，实现了RollingPolicy接口，该接口定义了rollover、getActiveFileName、getCompressionMode、setParent方法，其中FixedWindowRollingPolicy的rollover的实现是根据minIndex及maxIndex来的，要求maxIndex及minIndex相差不能超过20，rollover的时候从maxIndex-1开始到minIndex，把这些文件名的序号加1，然后当前文件重命名为minIndex，其中还配合压缩模式进行压缩处理。