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SpringBoot 2.0.3 源码解析

代码星球阅读(16)2020-09-13 收藏0次评论

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 

 

   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()

 

    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 一个公共方法,它可以创建线程并将其注册 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();
    }

                                       

    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。

    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);
        }
    }

    这里就可以看出来,这里是创建bean的核心方法了,头铁着又向下跟了一段,最终了了的发现其底层是cglib和jdk的aop切面来实现的。差点迷失在Spring庞大的代码里出不来。到这里run方法的流程就差不多执行完毕了。还有最后一步。

 

结语

  最后再来总结一下,springboot大体的执行流程

  1. prepareRefresh:预处理,包括属性验证等。

  2. prepareBeanFactory:主要对beanFactory设置了相关属性,并注册了3个Bean:environment,systemProperties和systemEnvironment供程序中注入使用。

  3. invokeBeanFactoryPostProcessors:执行所以BeanFactoryPostProcessor的postProcessBeanFactory方法。

  4. registerBeanPostProcessors:注册BeanFactoryPostProcessors到BeanFactory。

  5. initMessageSource:初始化MessageSource。

  6. initApplicationEventMulticaster:初始化事件广播器ApplicationEventMulticaster。

  7. registerListeners:事件广播器添加监听器,并广播早期事件。

  8. finishBeanFactoryInitialization:结束BeanFactory的实例化,也就是在这真正去创建单例Bean。

  9. finishRefresh:刷新的收尾工作。清理缓存,初始化生命周期处理器等等。

  10. destroyBeans:销毁创建的bean。

  11. cancelRefresh:取消刷新。

  12. resetCommonCaches:清理缓存。

  参考: https://www.cnblogs.com/zhisheng/p/8982845.html#4299273 https://www.jianshu.com/p/78c97ca56913

以上就是SpringBoot 2.0.3 源码解析的全部内容。