聊聊logback的FixedWindowRollingPolicy

序

本文主要研究一下logback的FixedWindowRollingPolicy

RollingPolicy

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

/**
 * A RollingPolicy is responsible for performing the rolling over
 * of the active log file. The RollingPolicy is also responsible
 * for providing the active log file, that is the live file where
 * logging output will be directed.
 * 
 * @author Ceki Gülcü
 */
public interface RollingPolicy extends LifeCycle {

    /**
     * Rolls over log files according to implementation policy.
     * 
     * 

     * 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.
     * 
     * 

     * With implementations such as {@link TimeBasedRollingPolicy}, this method
     * returns a new file name, where the actual output will be sent.
     * 
     * 

     * 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);
}
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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 setter
    protected String fileNamePatternStr;

    private FileAppender parent;

    // use to name files within zip file, i.e. the zipEntry
    FileNamePattern 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;
        }
    }

    //......
}    
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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;
    }

    //......
}    
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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();
    }
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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 file
                if (toRename.exists()) {
                    util.rename(toRenameStr, fileNamePattern.convertInt(i + 1));
                } else {
                    addInfo("Skipping roll-over for inexistent file " + toRenameStr);
                }
            }

            // move active file name to min
            switch (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;
            }
        }
    }
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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。