Spring boot源码分析-log日志系统（6）

说到日志系统的启动，我们首先看LoggingApplicationListener，这个类就是springboot日志系统加载的入口,可以看出实现了ApplicationListener，在上一节我们分析过ApplicationListener的运行方式

• 先看onApplicationEvent方法，从方法中我们可以看到，在springboot在几个阶段都会调用onApplicationEvent方法

        @Override    public void onApplicationEvent(ApplicationEvent event) {        //在springboot启动的时候        if (event instanceof ApplicationStartedEvent) {            onApplicationStartedEvent((ApplicationStartedEvent) event);        }        //springboot的Environment环境准备完成的时候        else if (event instanceof ApplicationEnvironmentPreparedEvent) {            onApplicationEnvironmentPreparedEvent(                    (ApplicationEnvironmentPreparedEvent) event);        }        //在springboot容器的环境设置完成以后        else if (event instanceof ApplicationPreparedEvent) {            onApplicationPreparedEvent((ApplicationPreparedEvent) event);        }        //容器关闭的时候        else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event)                .getApplicationContext().getParent() == null) {            onContextClosedEvent();        }        //容器启动失败的时候        else if (event instanceof ApplicationFailedEvent) {            onApplicationFailedEvent();        }    }

• onApplicationStartedEvent方法，在springboot开始启动时调用，主要工作为获取LoggingSystem然后调用beforeInitialize进行初始化LoggingSystem前的设置

    private void onApplicationStartedEvent(ApplicationStartedEvent event) {        this.loggingSystem = LoggingSystem                .get(event.getSpringApplication().getClassLoader());        this.loggingSystem.beforeInitialize();    }

首先设置LoggingSystem，当运行参数配置
-Dorg.springframework.boot.logging.LoggingSystem的时候，会根据配置的参数加载
默认支持的LoggingSystem有3个，当没有配置时默认加载LogbackLoggingSystem

    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("java.util.logging.LogManager",                "org.springframework.boot.logging.java.JavaLoggingSystem");        SYSTEMS = Collections.unmodifiableMap(systems);    }

• onApplicationEnvironmentPreparedEvent方法，在springboot完成环境初始化以后进行调用
*

    private void onApplicationEnvironmentPreparedEvent(            ApplicationEnvironmentPreparedEvent event) {        if (this.loggingSystem == null) {            this.loggingSystem = LoggingSystem                    .get(event.getSpringApplication().getClassLoader());        }        initialize(event.getEnvironment(), event.getSpringApplication().getClassLoader());    }

主要是设置相关的参数，进行初始化，

    protected void initialize(ConfigurableEnvironment environment,            ClassLoader classLoader) {        //设置相关的环境参数SystemProperty        new LoggingSystemProperties(environment).apply();        LogFile logFile = LogFile.get(environment);        if (logFile != null) {            logFile.applyToSystemProperties();        }        //environment参数debug   trace  设置日志级别        initializeEarlyLoggingLevel(environment);        //environment参数logging.config，初始化loggingSystem        initializeSystem(environment, this.loggingSystem, logFile);        //设置springboot默认的一些日志级别        initializeFinalLoggingLevels(environment, this.loggingSystem);        //注册ShutdownHook        registerShutdownHookIfNecessary(environment, this.loggingSystem);    }

new LoggingSystemProperties(environment).apply();的主要作用是设置logging.
exception-conversion-word
pattern.console
pattern.file
pattern.level到System环境中

    public void apply(LogFile logFile) {        RelaxedPropertyResolver propertyResolver = RelaxedPropertyResolver                .ignoringUnresolvableNestedPlaceholders(this.environment, "logging.");        setSystemProperty(propertyResolver, EXCEPTION_CONVERSION_WORD,                "exception-conversion-word");        setSystemProperty(propertyResolver, CONSOLE_LOG_PATTERN, "pattern.console");        setSystemProperty(propertyResolver, FILE_LOG_PATTERN, "pattern.file");        setSystemProperty(propertyResolver, LOG_LEVEL_PATTERN, "pattern.level");        setSystemProperty(PID_KEY, new ApplicationPid().toString());        if (logFile != null) {            logFile.applyToSystemProperties();        }    }

initializeEarlyLoggingLevel(environment);的主要作用是根据environment环境中的debug或者trace属性设置日志级别springBootLogging（后面代码会使用到）

    private void initializeEarlyLoggingLevel(ConfigurableEnvironment environment) {        if (this.parseArgs && this.springBootLogging == null) {            if (isSet(environment, "debug")) {                this.springBootLogging = LogLevel.DEBUG;            }            if (isSet(environment, "trace")) {                this.springBootLogging = LogLevel.TRACE;            }        }    }

initializeFinalLoggingLevels(environment, this.loggingSystem);做了两件事
1设置springboot内置的log日志级别 debug或者trace
通过logging.level.* 设置第三方的包的日志

    static {        LOG_LEVEL_LOGGERS = new LinkedMultiValueMap<LogLevel, String>();        LOG_LEVEL_LOGGERS.add(LogLevel.DEBUG, "org.springframework.boot");        LOG_LEVEL_LOGGERS.add(LogLevel.TRACE, "org.springframework");        LOG_LEVEL_LOGGERS.add(LogLevel.TRACE, "org.apache.tomcat");        LOG_LEVEL_LOGGERS.add(LogLevel.TRACE, "org.apache.catalina");        LOG_LEVEL_LOGGERS.add(LogLevel.TRACE, "org.eclipse.jetty");        LOG_LEVEL_LOGGERS.add(LogLevel.TRACE, "org.hibernate.tool.hbm2ddl");        LOG_LEVEL_LOGGERS.add(LogLevel.DEBUG, "org.hibernate.SQL");    }