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@Overridepublic void initialize(LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) { // 如果传递了日志配置文件，调用initializeWithSpecificConfig方法，使用指定的文件 if (StringUtils.hasLength(configLocation)) { initializeWithSpecificConfig(initializationContext, configLocation, logFile); return; } // 没有传递日志配置文件的话调用initializeWithConventions方法，使用约定俗成的方式 initializeWithConventions(initializationContext, logFile);}
private void initializeWithSpecificConfig( LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) { // 处理日志配置文件中的占位符 configLocation = SystemPropertyUtils.resolvePlaceholders(configLocation); loadConfiguration(initializationContext, configLocation, logFile);}
private void initializeWithConventions( LoggingInitializationContext initializationContext, LogFile logFile) { // 获取自初始化的日志配置文件，该方法会使用getStandardConfigLocations抽象方法得到的文件数组 // 然后进行遍历，如果文件存在，返回对应的文件目录。注意这里的文件指的是classpath下的文件 String config = getSelfInitializationConfig(); // 如果找到对应的日志配置文件并且logFile为null(logFile为null表示只有console会输出) if (config != null && logFile == null) { // 调用reinitialize方法重新初始化 // 默认的reinitialize方法不做任何处理，logback,log4j和log4j2覆盖了这个方法，会进行处理 reinitialize(initializationContext); return; } // 如果没有找到对应的日志配置文件 if (config == null) { // 调用getSpringInitializationConfig方法获取日志配置文件 // 该方法与getSelfInitializationConfig方法的区别在于getStandardConfigLocations方法得到的文件数组内部遍历的逻辑 // getSelfInitializationConfig方法直接遍历并判断classpath下是否存在对应的文件 // getSpringInitializationConfig方法遍历后判断的文件名会在后缀前加上 "-spring" 字符串 // 比如查找logback.xml文件，getSelfInitializationConfig会直接查找classpath下是否存在logback.xml文件，而getSpringInitializationConfig方法会判断classpath下是否存在logback-spring.xml文件 config = getSpringInitializationConfig(); } // 如果找到了对应的日志配置文件 if (config != null) { // 调用loadConfiguration抽象方法，让子类实现 loadConfiguration(initializationContext, config, logFile); return; } // 还是没找到日志配置文件的话，调用loadDefaults抽象方法加载，让子类实现 loadDefaults(initializationContext, logFile);}
protected abstract String[] getStandardConfigLocations();
protected abstract void loadConfiguration( LoggingInitializationContext initializationContext, String location, LogFile logFile);
protected abstract void loadDefaults( LoggingInitializationContext initializationContext, LogFile logFile); 

// LogbackLoggingSystem.class
// 根据上面AbstractLoggingSystem的分析// 使用logback日志库的时候会查找classpath下是否存在这些文件// logback-test.groovy、logback-test.xml、logback.groovy、logback.xml以及// logback-test-spring.groovy、logback-test-spring.xml、logback-spring.groovy、logback-spring.xml@Overrideprotected String[] getStandardConfigLocations() { return new String[] { "logback-test.groovy", "logback-test.xml", "logback.groovy", "logback.xml" };}
// logback具体的初始化加载过程@Overrideprotected void loadConfiguration(LoggingInitializationContext initializationContext, String location, LogFile logFile) { // 调用父类Slf4JLoggingSystem的loadConfiguration方法 super.loadConfiguration(initializationContext, location, logFile); // 获取slf4j内部的LoggerContext LoggerContext loggerContext = getLoggerContext(); // logback环境的一些配置配置处理 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 ? "\n" : ""); errors.append(status.toString()); } } if (errors.length() > 0) { throw new IllegalStateException( "Logback configuration error " + "detected: \n" + errors); }}
// 没找到日志配置文件的话使用loadDefaults方法加载@Overrideprotected void loadDefaults(LoggingInitializationContext initializationContext, LogFile logFile) { // 获取slf4j内部的LoggerContext LoggerContext context = getLoggerContext(); stopAndReset(context); LogbackConfigurator configurator = new LogbackConfigurator(context); context.putProperty("LOG_LEVEL_PATTERN", initializationContext.getEnvironment().resolvePlaceholders( "${logging.pattern.level:${LOG_LEVEL_PATTERN:%5p}}")); // 构造默认的console Appender。如果logFile不为空，还会构造file Appender new DefaultLogbackConfiguration(initializationContext, logFile) .apply(configurator); context.setPackagingDataEnabled(true);}
// logback的清除工作@Overridepublic void cleanUp() { super.cleanUp(); getLoggerContext().getStatusManager().clear();}
// 动态设置logger的level@Overridepublic void setLogLevel(String loggerName, LogLevel level) { getLogger(loggerName).setLevel(LEVELS.get(level));}
// 清除后的一些工作// ShutdownHandler会调用LoggerContext的stop方法@Overridepublic Runnable getShutdownHandler() { return new ShutdownHandler();} 

// spring-boot-version.jar/META-INF/spring.factories# Application Listenersorg.springframework.context.ApplicationListener=\org.springframework.boot.builder.ParentContextCloserApplicationListener,\org.springframework.boot.context.FileEncodingApplicationListener,\org.springframework.boot.context.config.AnsiOutputApplicationListener,\org.springframework.boot.context.config.ConfigFileApplicationListener,\org.springframework.boot.context.config.DelegatingApplicationListener,\org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\org.springframework.boot.logging.ClasspathLoggingApplicationListener,\org.springframework.boot.logging.LoggingApplicationListener 

// SpringApplication.classprivate void initialize(Object[] sources) { if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); } this.webEnvironment = deduceWebEnvironment(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); // 使用工厂加载机制找到这些Listener setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass();}
// LoggingApplicationListener.class@Overridepublic void onApplicationEvent(ApplicationEvent event) { // SpringApplication的run方法执行的时候触发该事件 if (event instanceof ApplicationStartedEvent) { // onApplicationStartedEvent方法内部会先得到LoggingSystem，然后调用beforeInitialize方法 onApplicationStartedEvent((ApplicationStartedEvent) event); } // 环境信息准备好，ApplicationContext创建之前触发该事件 else if (event instanceof ApplicationEnvironmentPreparedEvent) { // onApplicationEnvironmentPreparedEvent方法内部会做一下几个事情 // 1. 读取配置文件中"logging."开头的配置，比如logging.pattern.level, logging.pattern.console等设置到系统属性中 // 2. 构造一个LogFile(LogFile是对日志对外输出文件的封装)，使用LogFile的静态方法get构造，会使用配置文件中logging.file和logging.path配置构造 // 3. 判断配置中是否配置了debug并为true，如果是，设置level的DEBUG，然后继续查看是否配置了trace并为true，如果是，设置level的TRACE // 4. 构造LoggingInitializationContext，查看是否配置了logging.config，如有配置，调用LoggingSystem的initialize方法并带上该参数，否则调用initialize方法并且configLocation为null // 5. 设置一些比如org.springframework.boot、org.springframework、org.apache.tomcat、org.apache.catalina、org.eclipse.jetty、org.hibernate.tool.hbm2ddl、org.hibernate.SQL这些包的log level，跟第3步的level一样 // 6. 查看是否配置了logging.register-shutdown-hook，如配置并设置为true，使用addShutdownHook的addShutdownHook方法加入LoggingSystem的getShutdownHandler onApplicationEnvironmentPreparedEvent( (ApplicationEnvironmentPreparedEvent) event); } // Spring容器创建好，并进行了部分操作之后触发该事件 else if (event instanceof ApplicationPreparedEvent) { // onApplicationPreparedEvent方法内部会把LoggingSystem注册到BeanFactory中(前期是BeanFactory中不存在name为springBootLoggingSystem的实例) onApplicationPreparedEvent((ApplicationPreparedEvent) event); } // Spring容器关闭的时候触发该事件 else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event) .getApplicationContext().getParent() == null) { // onContextClosedEvent方法内部调用LoggingSystem的cleanUp方法进行清除工作 onContextClosedEvent(); }}
private void onApplicationStartedEvent(ApplicationStartedEvent event) { // 一开始先使用LoggingSystem的静态方法get获取LoggingSystem // 静态方法get会从下面那段static代码块中得到的Map中进行遍历 // 如果对应的key(key是某个类的全名)在classloader中存在，那么会构造该key对应的value对应的LoggingSystem this.loggingSystem = LoggingSystem .get(event.getSpringApplication().getClassLoader()); this.loggingSystem.beforeInitialize();}
static { Map<String, String> systems = new LinkedHashMap<String, String>(); systems.put("ch.qos.logback.core.Appender", "org.springframework.boot.logging.logback.LogbackLoggingSystem"); systems.put("org.apache.logging.log4j.core.impl.Log4jContextFactory", "org.springframework.boot.logging.log4j2.Log4J2LoggingSystem"); systems.put("org.apache.log4j.PropertyConfigurator", "org.springframework.boot.logging.log4j.Log4JLoggingSystem"); systems.put("java.util.logging.LogManager", "org.springframework.boot.logging.java.JavaLoggingSystem"); SYSTEMS = Collections.unmodifiableMap(systems);}
private void onApplicationEnvironmentPreparedEvent( ApplicationEnvironmentPreparedEvent event) { if (this.loggingSystem == null) { this.loggingSystem = LoggingSystem .get(event.getSpringApplication().getClassLoader()); } initialize(event.getEnvironment(), event.getSpringApplication().getClassLoader());}
private void onApplicationPreparedEvent(ApplicationPreparedEvent event) { ConfigurableListableBeanFactory beanFactory = event.getApplicationContext() .getBeanFactory(); if (!beanFactory.containsBean(LOGGING_SYSTEM_BEAN_NAME)) { beanFactory.registerSingleton(LOGGING_SYSTEM_BEAN_NAME, this.loggingSystem); }}
private void onContextClosedEvent() { if (this.loggingSystem != null) { this.loggingSystem.cleanUp(); }} 

logging:  path: /tmp    

// LogFile.class@Overridepublic String toString() { // 如果配置了logging.file，直接使用该文件 if (StringUtils.hasLength(this.file)) { return this.file; } // 否则使用logging.path目录，在该目录下创建spring.log日志文件 String path = this.path; if (!path.endsWith("/")) { path = path + "/"; } return StringUtils.applyRelativePath(path, "spring.log");} 

<?xml version="1.0" encoding="UTF-8"?><configuration> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <encoder> <!--<pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger[%line] &#45;&#45; %msg%n</pattern>--> <pattern>%d{YYYY-MM-dd} [%thread] %-5level %logger[%line] -- %msg%n</pattern> </encoder> </appender>
 <root level="INFO"> <appender-ref ref="STDOUT"/> </root></configuration> 

logging:  config: classpath:my-logback.xml

public static LoggingSystem get(ClassLoader classLoader) { // SYSTEM_PROPERTY静态变量是LoggingSystem的类全名 String loggingSystem = System.getProperty(SYSTEM_PROPERTY); if (StringUtils.hasLength(loggingSystem)) { if (NONE.equals(loggingSystem)) { // None静态变量是值是none return new NoOpLoggingSystem(); } return get(classLoader, loggingSystem); } for (Map.Entry<String, String> entry : SYSTEMS.entrySet()) { if (ClassUtils.isPresent(entry.getKey(), classLoader)) { return get(classLoader, entry.getValue()); } } throw new IllegalStateException("No suitable logging system located");}