Can logback make a copy at rollover time?

Question

I have a logback configured using the RollingFileAppender to rollover to a new log file with the SizeAndTimeBasedFNATP policy. I have it set up to rollover to a new file based on the day or based on the size. At that time, it will also compress the old log into a zip file.

Something like this:

<appender name="xyz" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
        <fileNamePattern>%d{yyyy/MM/dd}/log.zip</fileNamePattern>
        <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
            <maxFileSize>100MB</maxFileSize>
        </timeBasedFileNamingAndTriggeringPolicy>
    </rollingPolicy>
</appender>

Is there a way to get logback to make a copy of the zipped log at rollover time to a second location? Note that I want to keep one copy in the original location, but copy the file to a second location. (I need to keep the file in the original location for some period of time, but then delete it. The copied file will stay present indefinitely.)

Answer 1

I figured out a way to do this by extending the TimeBasedRollingPolicy. It feels a bit hackish, but it works. You need to put your new policy class within the ch.qos.logback.core.rolling package because TimeBasedRollingPolicy does not make it easy to override just the functionality needed without being within the package.

public class DuplicatingTimeBasedRollingPolicy<E> extends TimeBasedRollingPolicy<E> {
    // root directory of log (so we can retain subdirectory structures in copy)
    String originalRoot;
    // root directory for secondary log location
    String duplicateRoot;

    @Override
    Future<?> asyncCompress(String nameOfFile2Compress,
            String nameOfCompressedFile, String innerEntryName)
            throws RolloverFailure {
        // Do standard async compression
        final Future<?> future = super.asyncCompress(nameOfFile2Compress, nameOfCompressedFile,
                innerEntryName);

        // Figure out the file name to copy to and from
        String extension = compressionMode == CompressionMode.ZIP ? ".zip" : ".gz";
        final String sourceFileName = nameOfCompressedFile + extension;
        final String destFileName = duplicateRoot + File.separator + sourceFileName.substring(originalRoot.length());

        new Thread(new Runnable() {

            @Override
            public void run() {
                try {
                    // Wait for compression to finish and then make a copy
                    future.get();
                    FileUtils.copyFile(new File(sourceFileName), new File(destFileName));
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();

        return future;
    }
}

Note that this specifically only works when using compression (zip or gz) at rollover. Could be modified to also work when no compression is used. I'm not sure if this is the best way to handle this. Any better ideas?