SpringBoot 2.0.3 源码解析

时间：2019-07-16 16:43:44 阅读：148 评论：0 收藏：0 [点我收藏+]

标签：factory 关机 rds rtu argument orm env ict ctf

前言

用SpringBoot也有很长一段时间了，一直是底层使用者，没有研究过其到底是怎么运行的，借此机会今天试着将源码读一下，在此记录。。。我这里使用的SpringBoot 版本是 2.0.3.RELEASE

源码解析

　　SpringApplication 的初始化

　　1.首先一个完整的SpringBoot项目一定会有个启动类，这里就是我们整个程序的入口；

@SpringBootApplication
public class TeachercommunitystudioApplication extends SpringBootServletInitializer{

    public static void main(String[] args) {
        SpringApplication.run(TeachercommunitystudioApplication.class, args);
    }
}

　　2.只有一行代码，调用了 SpringApplication的静态 run()方法，

//调用重载run方法
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
    return run(new Class[]{primarySource}, args);
}

//参数为Class<?>数组 1.+版本这里是Object
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
    return (new SpringApplication(primarySources)).run(args);
}

　　3.在run()方法中调用构造函数创建SrpingApplicatin的对象，入参其实就是启动类的class对象，并调用该对象的run方法。

   //resourceLoader这里传入的是null, primarySources就是有启动类的class对象
   public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
 　　　　//为成员变量sources复制，sources是set<String> 类型
　　　　 this.sources = new LinkedHashSet();
        this.bannerMode = Mode.CONSOLE;
        this.logStartupInfo = true;
        this.addCommandLineProperties = true;
        this.headless = true;
        this.registerShutdownHook = true;
        this.additionalProfiles = new HashSet();
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
　　　　　//primarySources就是启动类class对象
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
　　　　  /*① 程序类型 通过一个枚举类判断web程序类型，WebApplicationType枚举类中的字段
　　　　　     包括 响应式程序，none, servlet程序*/
        this.webApplicationType = this.deduceWebApplicationType();
　　　　  //② 初始化classPath下的所有可用的应用初始化器 ApplicationContextInitalizer
        this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
　　　　　//④ 初始化监听器 
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        //⑤ 获取main方法的类名
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

　　　　① SpringBoot 2.0以后引入WebApplicationType新特性，该类是个枚举类，deduceWebApplicationType()方法推断使用哪中web程序，默认servlet程序

    private WebApplicationType deduceWebApplicationType() {
        if (ClassUtils.isPresent("org.springframework.web.reactive.DispatcherHandler", (ClassLoader)null) && !ClassUtils.isPresent("org.springframework.web.servlet.DispatcherServlet", (ClassLoader)null)) {
            return WebApplicationType.REACTIVE;
        } else {
            String[] var1 = WEB_ENVIRONMENT_CLASSES;
            int var2 = var1.length;

            for(int var3 = 0; var3 < var2; ++var3) {
                String className = var1[var3];
                if (!ClassUtils.isPresent(className, (ClassLoader)null)) {
                    return WebApplicationType.NONE;
                }
            }
　　　　　　　　//默认servlet
            return WebApplicationType.SERVLET;
        }
    }

//枚举类，web应用程序种类
public enum WebApplicationType {
    NONE,
    SERVLET,  //servlet程序
    REACTIVE; //响应式程序

    private WebApplicationType() {
    }
}

　　　　② 给SpringApplication的成员变量 List<ApplicationContextInitializer<?>> initializers 赋值， initializers--初始化器集合

　　　　　　调用 setInitializers(Collection<? extends ApplicationContextInitializer<?>> initializers){ ...}方法。代码如下

    public void setInitializers(Collection<? extends ApplicationContextInitializer<?>> initializers) {
        this.initializers = new ArrayList();
        this.initializers.addAll(initializers);
    }

　　　　　在构造方法中调用 setInitializers(Collection<? extends ApplicationContextInitializer<?>>) 入参为方法 getSpringFactoriesInstances(Class<T> type) 获取Srping工厂初始化器的返回值

　　private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
        return this.getSpringFactoriesInstances(type, new Class[0]);
    }

    private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        //获取所有BeanFactory的名字 
　　　　 ③ Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
　　　　 //创建工厂实例
        List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
        AnnotationAwareOrderComparator.sort(instances);//排序
        return instances;
    }

　　private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) {
        List<T> instances = new ArrayList(names.size());
        Iterator var7 = names.iterator();
        while(var7.hasNext()) {
            String name = (String)var7.next();

            try {
　　　　　　　　　 //实例数容器中的BeanFactory（这里指ApplicationContextInitializer）
                Class<?> instanceClass = ClassUtils.forName(name, classLoader);
                Assert.isAssignable(type, instanceClass);
　　　　　　　　　　//反射机制获取到构造方法对象，执行实例化
                Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
                T instance = BeanUtils.instantiateClass(constructor, args);
                instances.add(instance);
            } catch (Throwable var12) {
                throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, var12);
            }
        }

        return instances;
    }

　　　　③ SpringFactoriesLoader.loadFactoryNames(type, classLoader) 方法，从META/Spring.factories的资源文件中，读取key为ApplicationContextInitialiner对应的值　　

　　　　　从下面的代码我们可以看到，根据从构造方法中 ApplicationContextInitializer.class对象获取到ApplicationContextInitializer的类名路径，然后根据该类名路径

　　　　　从 META/Spring.factoryes 文件中获取对应的值，如下图

    public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
　　　　 //获取到类的全路径名称
        String factoryClassName = factoryClass.getName();
　　　　　return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
    }

    private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            try {
                Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                LinkedMultiValueMap result = new LinkedMultiValueMap();

                while(urls.hasMoreElements()) {
　　　　　　　　　 　　...
　　　　　　　　　 }
　　　　　　　　　　...
　　　　　　  }
　　　　　　　　...
　　　　  }
　　}

　　META-INF/spring.factories文件的内容，及ApplicationContextInitializer所对应的值　

　技术图片

　　可以看到，这里得到的值有四个类 ConfigurationWarningsApplicationContextInitializer、ContextIdApplicationContextInitializer、DelegatingApplicationContextInitializer、ServerPortInfoApplicationContextInitializer

　　所以 List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);这一步得到的List<T>的值就是他们四个的实例

    public void setInitializers(Collection<? extends ApplicationContextInitializer<?>> initializers) {
        this.initializers = new ArrayList();
        this.initializers.addAll(initializers);
    }

　　所以成员变量 initializers 的初始化变量值其实就是以上四个类的对象组成的List

　　　　④ 初始化监听器方法 this.setListeners()

　　　　　this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));

　　　　　整体流程和初始化应用初始化器类似，只不过从 META-INF/spring.factories 中获取的key为 ApplicationListener 的值，然后实例化几个对象后，封装为集合赋值给 this.setListeners()

技术图片

　　　　⑤ this.mainApplicationClass = this.deduceMainApplicationClass(); 获取main方法的类名

　　private Class<?> deduceMainApplicationClass() {
        try {
            StackTraceElement[] stackTrace = (new RuntimeException()).getStackTrace();
            StackTraceElement[] var2 = stackTrace;
            int var3 = stackTrace.length;
　　　　　　　
　　　　　　　//遍历堆栈跟踪元素，获取到调用当前类的方法判断是否为（"main"），是的话返回main所在的类名
            for(int var4 = 0; var4 < var3; ++var4) {

　　　　　　　　　StackTraceElement stackTraceElement = var2[var4];

if ("main".equals(stackTraceElement.getMethodName())) {
                    return Class.forName(stackTraceElement.getClassName());
                }
            }
        } catch (ClassNotFoundException var6) {
        }

        return null;
    }

　　2.run方法的执行流程

　　上面的流程执行完毕后，SpringApplication类就初始化完毕了，我们得到一个SpringApplication对象，然后掉用该对象的run()方法。run方法返回值为ConfigurableApplicationContext ---继承自---> ApplicationContext

　　run()方法内都做了什么事情呢，简单来说就是：

　　　　1）准备Spring的环境，

　　　　2）打印banner

　　　　3）通过spring环境准备上下文 ApplicationContext

　　　　4）刷新上下文，即真正去准备项目的Spring环境

　　下面我们根据代码来分析一下。

    public ConfigurableApplicationContext run(String... args) {
        // 声明一个秒表。计算并打印出程序耗时
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        // 程序异常报告
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        // ①设置系统为Headless模式
        this.configureHeadlessProperty();
        // ② 初始化SrpingApplicationRunListeners监听器
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        Collection exceptionReporters;
        try {
　　　　　　  // 初始化应用参数，参数为main方法中传入的args
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

　　　　　　  // ③ 根据listeners和 applicationArguments 应用参数 来配置SpringBoot的应用环境
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);

　　　　　　  // 根据环境配置去除要忽略的 bean信息
   　　　　  this.configureIgnoreBeanInfo(environment);
　　　　　　　// Banner打印，这里就不再多说了
            Banner printedBanner = this.printBanner(environment);

            /* ④ 根据 webApplicationType 应用类型来确定该 SpringBoot 项目应该创建什么类型的应用上下文 ApplicationContext
　　　　　　　　　如果没有明确的设置应用程序上下文会返回合适的默认值， */
            context = this.createApplicationContext();

            /* 和上面说的getSpringFactoriesInstances是一个套路，从META-INF/springfactories中获取键为SpringBootExceptionReporter的value
　　　　　　     然后将这些值使用反射，进行实例化返回一个集合 */
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);

　　　　     // ⑤ 完成整个容器的创建于启动以及 bean的注入功能
　　　　     this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
　　　　     // ⑥ 刷新上下文 
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }

　　　　① 设置系统为Headless模式

　　　　　Headess模式是系统的一种配置模式，在系统缺少显示设备，鼠标键盘等外设时可以使用该模式。一般是在程序开始激活headless模式，告诉程序，现在你要工作在Headless mode下，就不要指望硬件帮忙了，你得自力更生，依靠系统的计算能力模拟出这些特性来。

   private boolean headless;
   
　　//构造函数中
   this.headless = true;

　　private void configureHeadlessProperty() {
        System.setProperty("java.awt.headless", System.getProperty("java.awt.headless", Boolean.toString(this.headless)));
    }

　　　　② 初始化SrpingApplicationRunListeners监听器

　　　　这里依然调用 getSpringFactoriesInstances（）方法，和上面基本是一样的套路，从 META-INF/spring.factories 中获取键 SpringApplicationRunListener 的 value.　

        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            context = this.createApplicationContext();
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } 

　　　　 try {

　　    　　listeners.running(context);
   　　 　　return context;
　　　　}

　　// getSpringFactoriesInstances()方法和构造函数中的应用程序初始化类的初始化过程是同一个方法，基本流程就是从META-INF/spring.factories 配置文件里根据键取值
　　private SpringApplicationRunListeners getRunListeners(String[] args) {
        Class<?>[] types = new Class[]{SpringApplication.class, String[].class};
        return new SpringApplicationRunListeners(logger, this.getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
    }

　　　　③ 根据listeners和 applicationArguments 应用参数来配置SpringBoot的应用环境

　　// environment成员变量， 在构造函数中未赋值
　　private ConfigurableEnvironment environment;
　　private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
        ConfigurableEnvironment environment = this.getOrCreateEnvironment();
　　     // 配置环境
        this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
        listeners.environmentPrepared((ConfigurableEnvironment)environment);
        this.bindToSpringApplication((ConfigurableEnvironment)environment);
        if (this.webApplicationType == WebApplicationType.NONE) {
            environment = (new EnvironmentConverter(this.getClassLoader())).convertToStandardEnvironmentIfNecessary((ConfigurableEnvironment)environment);
        }

        ConfigurationPropertySources.attach((Environment)environment);
        return (ConfigurableEnvironment)environment;
    }
    // environment不为null直接返回，为null则新建
    private ConfigurableEnvironment getOrCreateEnvironment() {
        if (this.environment != null) {
            return this.environment;
        } else {
            return (ConfigurableEnvironment)(this.webApplicationType == WebApplicationType.SERVLET ? new StandardServletEnvironment() : new StandardEnvironment());
        }
    }

　　 // 配置环境
    protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
        this.configurePropertySources(environment, args);  //配置要使用的属性源 PropertySources
        this.configureProfiles(environment, args);　　//配置要使用的Profiles
    }

    // 将环境绑定到 SpringApplication
    protected void bindToSpringApplication(ConfigurableEnvironment environment) {
        try {
            Binder.get(environment).bind("spring.main", Bindable.ofInstance(this));
        } catch (Exception var3) {
            throw new IllegalStateException("Cannot bind to SpringApplication", var3);
        }
    }

　　　　④ 根据 webApplicationType 应用类型创建不同类型的ApplicationContext，未指定的话返回默认的ApplicationContext

    protected ConfigurableApplicationContext createApplicationContext() {
        Class<?> contextClass = this.applicationContextClass;
        if (contextClass == null) {
            try {
                switch(this.webApplicationType) {
                case SERVLET:
                    contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
                    break;
                case REACTIVE:
                    contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
                    break;
                default:
                    contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
                }
            } catch (ClassNotFoundException var3) {
                throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
            }
        }

        return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
    }

　　　　⑤ 完成整个容器的创建、启动以及 bean 的注入功能

    private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
        // 将上面获取到的 environment(配置环境类) 设置给创建好的Application
        context.setEnvironment(environment);

　　     // a. 该方法对 context 进行了预设置，设置了 ResourceLoader 和 ClassLoader，并向 bean 工厂中添加了一个beanNameGenerator 
        this.postProcessApplicationContext(context);

　　     // b. 在刷新前将 ApplicationContextInitializer 应用于上下文
        this.applyInitializers(context);
        listeners.contextPrepared(context);
        if (this.logStartupInfo) {// 启动日志
            this.logStartupInfo(context.getParent() == null);
            this.logStartupProfileInfo(context);
        }

        context.getBeanFactory().registerSingleton("springApplicationArguments", applicationArguments);
        if (printedBanner != null) {
            context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
        }

        Set<Object> sources = this.getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
        this.load(context, sources.toArray(new Object[0]));
        listeners.contextLoaded(context);
    }

　　　　　　a. postProcessApplicationContext(context); 对context 进行了预设值，设置了 ResourceLoader 和 ClassLoader, 并向bean工厂中添加了一个BeanNameGenerator。

    protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
　　     // 给ApplicationContext设置BeanNameGenerator;
        if (this.beanNameGenerator != null) {
            context.getBeanFactory().registerSingleton("org.springframework.context.annotation.internalConfigurationBeanNameGenerator", this.beanNameGenerator);
        }

        if (this.resourceLoader != null) {
　　　　      // 设置ResourceLoader 设置资源加载器 
            if (context instanceof GenericApplicationContext) {
                ((GenericApplicationContext)context).setResourceLoader(this.resourceLoader);
            }
　　　　     // 给ApplicationContext 设置 ClassLoader类加载器
            if (context instanceof DefaultResourceLoader) {
                ((DefaultResourceLoader)context).setClassLoader(this.resourceLoader.getClassLoader());
            }
        }

    }

　　　　　　b. 刷新前将所有ApplicationContextInitializer 应用于上下文

    protected void applyInitializers(ConfigurableApplicationContext context) {
        Iterator var2 = this.getInitializers().iterator();

        while(var2.hasNext()) {
            ApplicationContextInitializer initializer = (ApplicationContextInitializer)var2.next();
            Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(), ApplicationContextInitializer.class);
            Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
            initializer.initialize(context);
        }

    }

　　　　　　c. 主要是加载各种beans 到Application对象中，sources和primarySources，primarySources就是构造函数的入参，启动类的class对象

   // 获取所有资源列表
　　public Set<Object> getAllSources() {
        Set<Object> allSources = new LinkedHashSet();
        if (!CollectionUtils.isEmpty(this.primarySources)) {
            allSources.addAll(this.primarySources);
        }

        if (!CollectionUtils.isEmpty(this.sources)) {
            allSources.addAll(this.sources);
        }

        return Collections.unmodifiableSet(allSources);
    }

　　 // 加载各种bean到ApplicationContext对象中
    protected void load(ApplicationContext context, Object[] sources) {
        if (logger.isDebugEnabled()) {
            logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
        }

        BeanDefinitionLoader loader = this.createBeanDefinitionLoader(   // (2)
　　　　　　　　　　　　　this.getBeanDefinitionRegistry(context), sources); // (1)
        if (this.beanNameGenerator != null) {
            loader.setBeanNameGenerator(this.beanNameGenerator);
        }

        if (this.resourceLoader != null) {
            loader.setResourceLoader(this.resourceLoader);
        }

        if (this.environment != null) {
            loader.setEnvironment(this.environment);
        }

        loader.load(); // (3)
    }

　　　　　　　　(1) getBeanDefinitionRegistry(ApplicationContext context) 获取bean定义注册表

    private BeanDefinitionRegistry getBeanDefinitionRegistry(ApplicationContext context) {
        if (context instanceof BeanDefinitionRegistry) {
            return (BeanDefinitionRegistry)context;
        } else if (context instanceof AbstractApplicationContext) {
            return (BeanDefinitionRegistry)((AbstractApplicationContext)context).getBeanFactory();
        } else {
            throw new IllegalStateException("Could not locate BeanDefinitionRegistry");
        }
    }

　　　　　　　 (2) createBeanDefinitionLoader(BeanDefinitionRegistry registry, Object[] sources)

　　　　　　　　　通过BeanDefinitionLoader的构造方法把参数（注册表、资源）传进去，然后创建BeanDefinitionLoader。

    protected BeanDefinitionLoader createBeanDefinitionLoader(BeanDefinitionRegistry registry, Object[] sources) {
        return new BeanDefinitionLoader(registry, sources);
    }

　　　　　　　 (3) load() 调用BeanDefinitionLoader 对象的方法 load();把资源全部加载

    // 遍历所有资源
    public int load() {
        int count = 0;
        Object[] var2 = this.sources;
        int var3 = var2.length;

        for(int var4 = 0; var4 < var3; ++var4) {
            Object source = var2[var4];
            count += this.load(source);
        }

        return count;
    }

    // 根据资源的类型，调用不同的重载方法进行加载
    private int load(Object source) {
        Assert.notNull(source, "Source must not be null");
        if (source instanceof Class) {
            return this.load((Class)source);
        } else if (source instanceof Resource) {
            return this.load((Resource)source);
        } else if (source instanceof Package) {
            return this.load((Package)source);
        } else if (source instanceof CharSequence) {
            return this.load((CharSequence)source);
        } else {
            throw new IllegalArgumentException("Invalid source type " + source.getClass());
        }
    }

　　　　⑥ 刷新上下文

    private void refreshContext(ConfigurableApplicationContext context) {
        this.refresh(context); // a. 刷新底层的 ApplicationContext
        if (this.registerShutdownHook) {
            try {
　　　　　　　　   /* registerShutdownHook 是一个公共方法，它可以创建线程并将其注册到 Java 虚拟机，
　　                以便在关机时运行，以关闭 ApplicationContext  */
                context.registerShutdownHook();
            } catch (AccessControlException var3) {
            }
        }
    }

　　　　　　a. refresh ( ApplicationContext context ) 刷新底层的ApplicationContext

　　　　　　refresh()调用了 ApplicationContext 的一个子接口的实现类AvstractApplicationContext (抽象类) 中的 refresh() 方法

    protected void refresh(ApplicationContext applicationContext) {
        Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
        ((AbstractApplicationContext)applicationContext).refresh();
    }

技术图片

    public void refresh() throws BeansException, IllegalStateException {
        synchronized(this.startupShutdownMonitor) {
　　　　　　  // 准备刷新上下文
            this.prepareRefresh();
　　　　　　  // 通知子类刷新内部Bean工厂
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
　　　　　　  // 准备Bean工厂， 在上下文中使用
            this.prepareBeanFactory(beanFactory);

            try {
　　　　　　      // 允许在上下文子类中对Bean工厂进行后处理
                this.postProcessBeanFactory(beanFactory);
　　　　         // 调用上下文中注册为Bean 的工厂处理器
                this.invokeBeanFactoryPostProcessors(beanFactory);
　　　　　　      // 注册拦截Bean创建的bean处理器
                this.registerBeanPostProcessors(beanFactory);
　　　　　　      // 注册上下文中的消息源
                this.initMessageSource();
　　　　　　      // 初始化事件广播机制
                this.initApplicationEventMulticaster();
　　　　　　      // 在特定上下文子类中初始化其他特殊Bean
                this.onRefresh();
　　　　　　      // 检查注册监听器Bean
                this.registerListeners();
　　　　　　      // 实例化所有剩余单例（非惰性）完成BeanFactory的初始化
                this.finishBeanFactoryInitialization(beanFactory);
　　　　　　      // 发布相应的事件
                this.finishRefresh();
            } catch (BeansException var9) {
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
                }
　　　　　　      // 销毁已创建的单例，避免资源的浪费
                this.destroyBeans();
　　　　　　      // 重置活动的标志
                this.cancelRefresh(var9);
                throw var9;
            } finally {
　　　　　　      // 重置Spring中的常见内省缓存
                this.resetCommonCaches();
            }

        }
    }

　　　　　通过以上代码可以看到，这里在做各种初始化工作，后面有个 finishBeanFactoryInitialization() 方法完成BeanFactory的初始化，我们重点看下这个；该方法进行了非懒加载beans的初始化工作。进去看一下。

技术图片

　　　　我们看到，最后调用了 beanFactory的 preInstantiateSingletons()；再进去看一下，beanFactory - -ConfigurableListableBeanFactory 只有一个实现类 DefaultListableBeanFactory 实现了该方法，进去看看具体如何实现的。

    public void preInstantiateSingletons() throws BeansException {
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Pre-instantiating singletons in " + this);
        }

        List<String> beanNames = new ArrayList(this.beanDefinitionNames);
        Iterator var2 = beanNames.iterator();

        while(true) {
            String beanName;
            Object bean;
            do {
                while(true) {
                    RootBeanDefinition bd;
                    do {
                        do {
                            do {
                                if (!var2.hasNext()) {
                                    var2 = beanNames.iterator();

                                    while(var2.hasNext()) {
                                        beanName = (String)var2.next();
                                        Object singletonInstance = this.getSingleton(beanName);
                                        if (singletonInstance instanceof SmartInitializingSingleton) {
                                            SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton)singletonInstance;
                                            if (System.getSecurityManager() != null) {
                                                AccessController.doPrivileged(() -> {
                                                    smartSingleton.afterSingletonsInstantiated();
                                                    return null;
                                                }, this.getAccessControlContext());
                                            } else {
                                                smartSingleton.afterSingletonsInstantiated();
                                            }
                                        }
                                    }

                                    return;
                                }

                                beanName = (String)var2.next();
                                bd = this.getMergedLocalBeanDefinition(beanName);
                            } while(bd.isAbstract());
                        } while(!bd.isSingleton());
                    } while(bd.isLazyInit());

                    if (this.isFactoryBean(beanName)) {
                        bean = this.getBean("&" + beanName);
                        break;
                    }

                    this.getBean(beanName);
                }
            } while(!(bean instanceof FactoryBean));

            FactoryBean<?> factory = (FactoryBean)bean;
            boolean isEagerInit;
            if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                SmartFactoryBean var10000 = (SmartFactoryBean)factory;
                ((SmartFactoryBean)factory).getClass();
                isEagerInit = (Boolean)AccessController.doPrivileged(var10000::isEagerInit, this.getAccessControlContext());
            } else {
                isEagerInit = factory instanceof SmartFactoryBean && ((SmartFactoryBean)factory).isEagerInit();
            }

            if (isEagerInit) {
                this.getBean(beanName);
            }
        }
    }

　　　　猛地一看有点多顿时不知从何下手，但仔细看看，好像整段代码都围绕着 getBean()来写的，由此推测getBean才是重头戏，找到重点那就跟踪看一下，发现进入了AbstractBeanFactory类，(好像有点熟悉,先不管继续向下看)，在getBean中最终调用了AbstractBeanFactory中的doGetBean()方法()。

    protected <T> T doGetBean(String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly) throws BeansException {
        String beanName = this.transformedBeanName(name);
        Object sharedInstance = this.getSingleton(beanName);
        Object bean;
        if (sharedInstance != null && args == null) {
            if (this.logger.isDebugEnabled()) {
                if (this.isSingletonCurrentlyInCreation(beanName)) {
                    this.logger.debug("Returning eagerly cached instance of singleton bean ‘" + beanName + "‘ that is not fully initialized yet - a consequence of a circular reference");
                } else {
                    this.logger.debug("Returning cached instance of singleton bean ‘" + beanName + "‘");
                }
            }

            bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
        } else {
            if (this.isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            BeanFactory parentBeanFactory = this.getParentBeanFactory();
            if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
                String nameToLookup = this.originalBeanName(name);
                if (parentBeanFactory instanceof AbstractBeanFactory) {
                    return ((AbstractBeanFactory)parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);
                }

                if (args != null) {
                    return parentBeanFactory.getBean(nameToLookup, args);
                }

                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }

            if (!typeCheckOnly) {
                this.markBeanAsCreated(beanName);
            }

            try {
                RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
                this.checkMergedBeanDefinition(mbd, beanName, args);
                String[] dependsOn = mbd.getDependsOn();
                String[] var11;
                if (dependsOn != null) {
                    var11 = dependsOn;
                    int var12 = dependsOn.length;

                    for(int var13 = 0; var13 < var12; ++var13) {
                        String dep = var11[var13];
                        if (this.isDependent(beanName, dep)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between ‘" + beanName + "‘ and ‘" + dep + "‘");
                        }

                        this.registerDependentBean(dep, beanName);

                        try {
                            this.getBean(dep);
                        } catch (NoSuchBeanDefinitionException var24) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "‘" + beanName + "‘ depends on missing bean ‘" + dep + "‘", var24);
                        }
                    }
                }

                if (mbd.isSingleton()) {
                    sharedInstance = this.getSingleton(beanName, () -> {
                        try {
                            return this.createBean(beanName, mbd, args);
                        } catch (BeansException var5) {
                            this.destroySingleton(beanName);
                            throw var5;
                        }
                    });
                    bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                } else if (mbd.isPrototype()) {
                    var11 = null;

                    Object prototypeInstance;
                    try {
                        this.beforePrototypeCreation(beanName);
                        prototypeInstance = this.createBean(beanName, mbd, args);
                    } finally {
                        this.afterPrototypeCreation(beanName);
                    }

                    bean = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                } else {
                    String scopeName = mbd.getScope();
                    Scope scope = (Scope)this.scopes.get(scopeName);
                    if (scope == null) {
                        throw new IllegalStateException("No Scope registered for scope name ‘" + scopeName + "‘");
                    }

                    try {
                        Object scopedInstance = scope.get(beanName, () -> {
                            this.beforePrototypeCreation(beanName);

                            Object var4;
                            try {
                                var4 = this.createBean(beanName, mbd, args);
                            } finally {
                                this.afterPrototypeCreation(beanName);
                            }

                            return var4;
                        });
                        bean = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                    } catch (IllegalStateException var23) {
                        throw new BeanCreationException(beanName, "Scope ‘" + scopeName + "‘ is not active for the current thread; consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", var23);
                    }
                }
            } catch (BeansException var26) {
                this.cleanupAfterBeanCreationFailure(beanName);
                throw var26;
            }
        }

        if (requiredType != null && !requiredType.isInstance(bean)) {
            try {
                T convertedBean = this.getTypeConverter().convertIfNecessary(bean, requiredType);
                if (convertedBean == null) {
                    throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
                } else {
                    return convertedBean;
                }
            } catch (TypeMismatchException var25) {
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Failed to convert bean ‘" + name + "‘ to required type ‘" + ClassUtils.getQualifiedName(requiredType) + "‘", var25);
                }

                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        } else {
            return bean;
        }
    }

　　　　在doGetBean()方法中看到createBean(); 该方法在这里并没有实现；由AbstractBeanFactory的实现类 AbstractAutowireCapableBeanFactory 实现了该方法；该类时一个抽象类。

    public Object createBean(Class<?> beanClass, int autowireMode, boolean dependencyCheck) throws BeansException {
        RootBeanDefinition bd = new RootBeanDefinition(beanClass, autowireMode, dependencyCheck);
        bd.setScope("prototype");
        return this.createBean(beanClass.getName(), bd, (Object[])null);
    }

    protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Creating instance of bean ‘" + beanName + "‘");
        }

        RootBeanDefinition mbdToUse = mbd;
        Class<?> resolvedClass = this.resolveBeanClass(mbd, beanName, new Class[0]);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        try {
            mbdToUse.prepareMethodOverrides();
        } catch (BeanDefinitionValidationException var9) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(), beanName, "Validation of method overrides failed", var9);
        }

        Object beanInstance;
        try {
            beanInstance = this.resolveBeforeInstantiation(beanName, mbdToUse);
            if (beanInstance != null) {
                return beanInstance;
            }
        } catch (Throwable var10) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", var10);
        }

        try {
            beanInstance = this.doCreateBean(beanName, mbdToUse, args);
            if (this.logger.isDebugEnabled()) {
                this.logger.debug("Finished creating instance of bean ‘" + beanName + "‘");
            }

            return beanInstance;
        } catch (ImplicitlyAppearedSingletonException | BeanCreationException var7) {
            throw var7;
        } catch (Throwable var8) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", var8);
        }
    }