OnShutdownCompressingRollingFileAppender the compresses on logging context stop

OnShutdownCompressingRollingFileAppender.java

package de.jonasgroeger.logback;

import ch.qos.logback.core.LogbackException;
import ch.qos.logback.core.rolling.RollingFileAppender;
import ch.qos.logback.core.rolling.RollingPolicy;
import ch.qos.logback.core.rolling.TimeBasedFileNamingAndTriggeringPolicy;
import ch.qos.logback.core.rolling.TimeBasedRollingPolicy;
import ch.qos.logback.core.rolling.helper.CompressionMode;
import ch.qos.logback.core.rolling.helper.Compressor;

import static ch.qos.logback.core.CoreConstants.UNBOUND_HISTORY;

/**
 * The logging context around a Spring application is larger than the application itself. This is based on the
 * requirement that Spring wants to log things when it starts.
 * <p>
 * The default RollingFileAppender will only compress on rollover and on application start if the filename stays the
 * same. Since when deploying applications in a container environment like OpenShift, the hostname of a machine
 * always something like service-1-asidj. When using this hostname as the logfile name, the RollingFileAppender cannot
 * roll old logs on start. This is what the OnShutdownCompressingRollingFileAppender tries to solve.
 * <p>
 * The OnShutdownCompressingRollingFileAppender compresses the logs after Spring has shutdown and the logging context is
 * closing. This is when stop() is called.
 *
 * @author Jonas Gröger
 */
public class OnShutdownCompressingRollingFileAppender<E> extends RollingFileAppender<E> {

    @Override
    public void start() {
        RollingPolicy rollingPolicy = getRollingPolicy();

        if (rollingPolicy == null) {
            throw new LogbackException("No RollingPolicy was set for the OnShutdownCompressingRollingFileAppender named " + getName());
        }

        if (!(rollingPolicy instanceof TimeBasedRollingPolicy)) {
            throw new LogbackException("The OnShutdownCompressingRollingFileAppender only works with the TimeBasedRollingPolicy.");
        }

        if (((TimeBasedRollingPolicy) rollingPolicy).getMaxHistory() != UNBOUND_HISTORY) {
            throw new LogbackException(
                    "The OnShutdownCompressingRollingFileAppender is not compatible with the <maxHistory> setting " +
                            "since future application starts cannot find older logfiles based on the logfile name " +
                            "pattern. The OnShutdownCompressingFileAppender will however work when you do not " +
                            "redeploy your application."
            );
        }

        if (((TimeBasedRollingPolicy) rollingPolicy).isCleanHistoryOnStart()) {
            throw new LogbackException(
                    "The OnShutdownCompressingRollingFileAppender is not fully compatible with the <cleanHistoryOnStart> setting " +
                            "since future application starts cannot find older logfiles based on the logfile name " +
                            "pattern. The OnShutdownCompressingRollingFileAppender will however work when you do not " +
                            "redeploy your application."
            );
        }

        super.start();
    }

    @Override
    public void stop() {
        super.stop();

        TimeBasedRollingPolicy rollingPolicy = (TimeBasedRollingPolicy) getRollingPolicy();
        TimeBasedFileNamingAndTriggeringPolicy triggeringPolicy = rollingPolicy.getTimeBasedFileNamingAndTriggeringPolicy();
        CompressionMode compressionMode = rollingPolicy.getCompressionMode();

        String logFile = getFile();
        String logFileCompressed = triggeringPolicy.getCurrentPeriodsFileNameWithoutCompressionSuffix();

        Compressor c = new Compressor(compressionMode);
        c.setContext(this.context);
        c.compress(logFile, logFileCompressed, logFileCompressed);
    }
}