背景

项目之前是通过命令行参数-Dlogging.config指定日志配置文件的路径的，后面应用docker化时，需要将这个配置文件打到应用包中，因此翻了下spring boot源码，看都支持哪些路径。

spring boot初始化入口

如之前文章的分析,spring boot是通过LoggingApplicationListener监听到ApplicationEnvironmentPreparedEvent后开始初始化日志系统的。从源码可以看到，spring boot有三种方式去获取日志配置，优先级如下：

由配置项logging.config指定
约定的默认路径（“classpath:xx.xml”）
默认配置（由spring boot编码实现）

由配置项logging.config指定

日志初始化的入口函数为org.springframework.boot.context.logging.LoggingApplicationListener#initializeSystem

    public static final String CONFIG_PROPERTY = "logging.config";
	
	private void initializeSystem(ConfigurableEnvironment environment, LoggingSystem system, LogFile logFile) {
		LoggingInitializationContext initializationContext = new LoggingInitializationContext(environment);
		String logConfig = environment.getProperty(CONFIG_PROPERTY);
		if (ignoreLogConfig(logConfig)) {
			system.initialize(initializationContext, null, logFile);
		}
		else {
			try {
				system.initialize(initializationContext, logConfig, logFile);
			}
			catch (Exception ex) {
				......
		}
	}

org.springframework.boot.logging.AbstractLoggingSystem#initialize

	@Override
	public void initialize(LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) {
	    # 可以看到优先使用logging.config配置项指定的配置路径
		if (StringUtils.hasLength(configLocation)) {
			initializeWithSpecificConfig(initializationContext, configLocation, logFile);
			return;
		}
		initializeWithConventions(initializationContext, logFile);
	}

约定的默认路径

org.springframework.boot.logging.AbstractLoggingSystem#initializeWithConventions

	private void initializeWithConventions(LoggingInitializationContext initializationContext, LogFile logFile) {
	    # 优先获取自定义的日志配置文件
		String config = getSelfInitializationConfig();
		if (config != null && logFile == null) {
			// self initialization has occurred, reinitialize in case of property changes
			reinitialize(initializationContext);
			return;
		}
		# 没有自定义的这使用spring自己的日志配置文件
		if (config == null) {
			config = getSpringInitializationConfig();
		}
		if (config != null) {
			loadConfiguration(initializationContext, config, logFile);
			return;
		}
		# 上述两者都不存在的情况下，则使用编码的方式，配置日志的默认配置
		loadDefaults(initializationContext, logFile);
	}

不管是自定义的默认路径的日志配置文件还是spring自己的，都是在类路径上搜索（“classpath:xx.xml”），唯一的区别只是，两者的名字不一样而已。
自定义的会搜索"logback-test.groovy", “logback-test.xml”, “logback.groovy”, “logback.xml”；
spring自带的则会搜索"logback-test-spring.groovy", “logback-test-spring.xml”, “logback-spring.groovy”, “logback-spring.xml”；

	protected String getSelfInitializationConfig() {
		return findConfig(getStandardConfigLocations());
	}
	protected String[] getStandardConfigLocations() {
		return new String[] { "logback-test.groovy", "logback-test.xml", "logback.groovy", "logback.xml" };
	}
	
	protected String getSpringInitializationConfig() {
		return findConfig(getSpringConfigLocations());
	}
	protected String[] getSpringConfigLocations() {
		String[] locations = getStandardConfigLocations();
		# spring自己的配置文件就是在默认的自定义文件名上加“-spring”后缀
		for (int i = 0; i < locations.length; i++) {
			String extension = StringUtils.getFilenameExtension(locations[i]);
			locations[i] = locations[i].substring(0, locations[i].length() - extension.length() - 1) + "-spring."
					+ extension;
		}
		return locations;
	}

	private String findConfig(String[] locations) {
		for (String location : locations) {
			ClassPathResource resource = new ClassPathResource(location, this.classLoader);
			if (resource.exists()) {
				return "classpath:" + location;
			}
		}
		return null;
	}

默认配置（由spring boot编码实现）

org.springframework.boot.logging.logback.LogbackLoggingSystem#loadDefaults

	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);
	}