public abstract class LoggingSystem {

	public abstract void beforeInitialize();

	public void initialize(LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) {
	}

	public void cleanUp() {
	}

	public Runnable getShutdownHandler() {
		return null;
	}

	public Set<LogLevel> getSupportedLogLevels() {
		return EnumSet.allOf(LogLevel.class);
	}

	public void setLogLevel(String loggerName, LogLevel level) {
		throw new UnsupportedOperationException("Unable to set log level");
	}

	public List<LoggerConfiguration> getLoggerConfigurations() {
		throw new UnsupportedOperationException("Unable to get logger configurations");
	}

	public LoggerConfiguration getLoggerConfiguration(String loggerName) {
		throw new UnsupportedOperationException("Unable to get logger configuration");
	}				
}

static class NoOpLoggingSystem extends LoggingSystem {

		@Override
		public void beforeInitialize() {

		}

		@Override
		public void setLogLevel(String loggerName, LogLevel level) {

		}

		@Override
		public List<LoggerConfiguration> getLoggerConfigurations() {
			return Collections.emptyList();
		}

		@Override
		public LoggerConfiguration getLoggerConfiguration(String loggerName) {
			return null;
		}

	}

public abstract class AbstractLoggingSystem extends LoggingSystem {

	protected static final Comparator<LoggerConfiguration> CONFIGURATION_COMPARATOR = new LoggerConfigurationComparator(
			ROOT_LOGGER_NAME);

	private final ClassLoader classLoader;

	public AbstractLoggingSystem(ClassLoader classLoader) {
		this.classLoader = classLoader;
	}

	@Override
	public void beforeInitialize() {
	}

	@Override
	public void initialize(LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) {
		if (StringUtils.hasLength(configLocation)) {
			initializeWithSpecificConfig(initializationContext, configLocation, logFile);
			return;
		}
		initializeWithConventions(initializationContext, logFile);
	}

	/**
	 * Load sensible defaults for the logging system.
	 * @param initializationContext the logging initialization context
	 * @param logFile the file to load or {@code null} if no log file is to be written
	 */
	protected abstract void loadDefaults(LoggingInitializationContext initializationContext, LogFile logFile);

	/**
	 * Load a specific configuration.
	 * @param initializationContext the logging initialization context
	 * @param location the location of the configuration to load (never {@code null})
	 * @param logFile the file to load or {@code null} if no log file is to be written
	 */
	protected abstract void loadConfiguration(LoggingInitializationContext initializationContext, String location,
			LogFile logFile);

	/**
	 * Reinitialize the logging system if required. Called when
	 * {@link #getSelfInitializationConfig()} is used and the log file hasn't changed. May
	 * be used to reload configuration (for example to pick up additional System
	 * properties).
	 * @param initializationContext the logging initialization context
	 */
	protected void reinitialize(LoggingInitializationContext initializationContext) {
	}

	//......
}

public abstract class Slf4JLoggingSystem extends AbstractLoggingSystem {

	private static final String BRIDGE_HANDLER = "org.slf4j.bridge.SLF4JBridgeHandler";

	public Slf4JLoggingSystem(ClassLoader classLoader) {
		super(classLoader);
	}

	@Override
	public void beforeInitialize() {
		super.beforeInitialize();
		configureJdkLoggingBridgeHandler();
	}

	@Override
	public void cleanUp() {
		if (isBridgeHandlerAvailable()) {
			removeJdkLoggingBridgeHandler();
		}
	}

	@Override
	protected void loadConfiguration(LoggingInitializationContext initializationContext, String location,
			LogFile logFile) {
		Assert.notNull(location, "Location must not be null");
		if (initializationContext != null) {
			applySystemProperties(initializationContext.getEnvironment(), logFile);
		}
	}

	//......
}

private void configureJdkLoggingBridgeHandler() {
		try {
			if (isBridgeJulIntoSlf4j()) {
				removeJdkLoggingBridgeHandler();
				SLF4JBridgeHandler.install();
			}
		}
		catch (Throwable ex) {
			// Ignore. No java.util.logging bridge is installed.
		}
	}

private void removeJdkLoggingBridgeHandler() {
		try {
			removeDefaultRootHandler();
			SLF4JBridgeHandler.uninstall();
		}
		catch (Throwable ex) {
			// Ignore and continue
		}
	}

	private void removeDefaultRootHandler() {
		try {
			Logger rootLogger = LogManager.getLogManager().getLogger("");
			Handler[] handlers = rootLogger.getHandlers();
			if (handlers.length == 1 && handlers[0] instanceof ConsoleHandler) {
				rootLogger.removeHandler(handlers[0]);
			}
		}
		catch (Throwable ex) {
			// Ignore and continue
		}
	}

protected final void applySystemProperties(Environment environment, LogFile logFile) {
		new LoggingSystemProperties(environment).apply(logFile);
	}

	public void apply(LogFile logFile) {
		PropertyResolver resolver = getPropertyResolver();
		setSystemProperty(resolver, EXCEPTION_CONVERSION_WORD, "exception-conversion-word");
		setSystemProperty(PID_KEY, new ApplicationPid().toString());
		setSystemProperty(resolver, CONSOLE_LOG_PATTERN, "pattern.console");
		setSystemProperty(resolver, FILE_LOG_PATTERN, "pattern.file");
		setSystemProperty(resolver, FILE_CLEAN_HISTORY_ON_START, "file.clean-history-on-start");
		setSystemProperty(resolver, FILE_MAX_HISTORY, "file.max-history");
		setSystemProperty(resolver, FILE_MAX_SIZE, "file.max-size");
		setSystemProperty(resolver, FILE_TOTAL_SIZE_CAP, "file.total-size-cap");
		setSystemProperty(resolver, LOG_LEVEL_PATTERN, "pattern.level");
		setSystemProperty(resolver, LOG_DATEFORMAT_PATTERN, "pattern.dateformat");
		setSystemProperty(resolver, ROLLING_FILE_NAME_PATTERN, "pattern.rolling-file-name");
		if (logFile != null) {
			logFile.applyToSystemProperties();
		}
	}

public class LogbackLoggingSystem extends Slf4JLoggingSystem {

	private static final String CONFIGURATION_FILE_PROPERTY = "logback.configurationFile";

	private static final LogLevels<Level> LEVELS = new LogLevels<>();

	static {
		LEVELS.map(LogLevel.TRACE, Level.TRACE);
		LEVELS.map(LogLevel.TRACE, Level.ALL);
		LEVELS.map(LogLevel.DEBUG, Level.DEBUG);
		LEVELS.map(LogLevel.INFO, Level.INFO);
		LEVELS.map(LogLevel.WARN, Level.WARN);
		LEVELS.map(LogLevel.ERROR, Level.ERROR);
		LEVELS.map(LogLevel.FATAL, Level.ERROR);
		LEVELS.map(LogLevel.OFF, Level.OFF);
	}

	private static final TurboFilter FILTER = new TurboFilter() {

		@Override
		public FilterReply decide(Marker marker, ch.qos.logback.classic.Logger logger, Level level, String format,
				Object[] params, Throwable t) {
			return FilterReply.DENY;
		}

	};

	public LogbackLoggingSystem(ClassLoader classLoader) {
		super(classLoader);
	}

	@Override
	protected String[] getStandardConfigLocations() {
		return new String[] { "logback-test.groovy", "logback-test.xml", "logback.groovy", "logback.xml" };
	}

	//......
}

@Override
	public void beforeInitialize() {
		LoggerContext loggerContext = getLoggerContext();
		if (isAlreadyInitialized(loggerContext)) {
			return;
		}
		super.beforeInitialize();
		loggerContext.getTurboFilterList().add(FILTER);
	}

@Override
	public void initialize(LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) {
		LoggerContext loggerContext = getLoggerContext();
		if (isAlreadyInitialized(loggerContext)) {
			return;
		}
		super.initialize(initializationContext, configLocation, logFile);
		loggerContext.getTurboFilterList().remove(FILTER);
		markAsInitialized(loggerContext);
		if (StringUtils.hasText(System.getProperty(CONFIGURATION_FILE_PROPERTY))) {
			getLogger(LogbackLoggingSystem.class.getName()).warn("Ignoring '" + CONFIGURATION_FILE_PROPERTY
					+ "' system property. Please use 'logging.config' instead.");
		}
	}

@Override
	protected void loadDefaults(LoggingInitializationContext initializationContext, LogFile logFile) {
		LoggerContext context = getLoggerContext();
		stopAndReset(context);
		boolean debug = Boolean.getBoolean("logback.debug");
		if (debug) {
			StatusListenerConfigHelper.addOnConsoleListenerInstance(context, new OnConsoleStatusListener());
		}
		LogbackConfigurator configurator = debug ? new DebugLogbackConfigurator(context)
				: new LogbackConfigurator(context);
		Environment environment = initializationContext.getEnvironment();
		context.putProperty(LoggingSystemProperties.LOG_LEVEL_PATTERN,
				environment.resolvePlaceholders("${logging.pattern.level:${LOG_LEVEL_PATTERN:%5p}}"));
		context.putProperty(LoggingSystemProperties.LOG_DATEFORMAT_PATTERN, environment.resolvePlaceholders(
				"${logging.pattern.dateformat:${LOG_DATEFORMAT_PATTERN:yyyy-MM-dd HH:mm:ss.SSS}}"));
		context.putProperty(LoggingSystemProperties.ROLLING_FILE_NAME_PATTERN, environment
				.resolvePlaceholders("${logging.pattern.rolling-file-name:${LOG_FILE}.%d{yyyy-MM-dd}.%i.gz}"));
		new DefaultLogbackConfiguration(initializationContext, logFile).apply(configurator);
		context.setPackagingDataEnabled(true);
	}

@Override
	protected void loadConfiguration(LoggingInitializationContext initializationContext, String location,
			LogFile logFile) {
		super.loadConfiguration(initializationContext, location, logFile);
		LoggerContext loggerContext = getLoggerContext();
		stopAndReset(loggerContext);
		try {
			configureByResourceUrl(initializationContext, loggerContext, ResourceUtils.getURL(location));
		}
		catch (Exception ex) {
			throw new IllegalStateException("Could not initialize Logback logging from " + location, ex);
		}
		List<Status> statuses = loggerContext.getStatusManager().getCopyOfStatusList();
		StringBuilder errors = new StringBuilder();
		for (Status status : statuses) {
			if (status.getLevel() == Status.ERROR) {
				errors.append((errors.length() > 0) ? String.format("%n") : "");
				errors.append(status.toString());
			}
		}
		if (errors.length() > 0) {
			throw new IllegalStateException(String.format("Logback configuration error detected: %n%s", errors));
		}
	}

	private void configureByResourceUrl(LoggingInitializationContext initializationContext, LoggerContext loggerContext,
			URL url) throws JoranException {
		if (url.toString().endsWith("xml")) {
			JoranConfigurator configurator = new SpringBootJoranConfigurator(initializationContext);
			configurator.setContext(loggerContext);
			configurator.doConfigure(url);
		}
		else {
			new ContextInitializer(loggerContext).configureByResource(url);
		}
	}