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Spring容器启动(上)

Java光头强 • • Java • 阅读 179

导读：本篇文章讲解 Spring容器启动(上)，希望对大家有帮助，欢迎收藏，转发！站点地址：www.bmabk.com

在Bean的生命周期中，尤其是在初始化的过程中，会用到大量的BeanProcessor实现类的方法，对Bean实例进行一系列的操作，其中包括查找注入点、依赖注入、AOP等等，而这其中用到的BeanProcessor实现类的实例正是在Spring容器启动的过程中创建的，在启动的过程中不仅会创建BeanProcessor的实例，也会设置BeanFactory的类加载器、SpringEL表达式解析器、类型转化注册器，扫描类文件生成BeanDefinition以及初始化事件监听器，同时非懒加载单例Bean的实例化过程也是在Spring启动的过程中创建的

下面将简单介绍Spring启动过程中，都具体做了哪些工作？以AnnotationConfigApplicationContext容器为例

一、构造创建

通过AnnotationConfigApplicationContext并指定配置文件来创建Spring容器，而在有参构造方法内部，首先会去调用无参的构造方法，完成基本的初始化

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);

@ComponentScan("com.lizhi")
@EnableAsync
public class AppConfig {

   @Bean
   public UserService userService(){
      return new UserService();
   }
}

public AnnotationConfigApplicationContext(Class<?>... componentClasses) {
   // 构造DefaultListableBeanFactory、AnnotatedBeanDefinitionReader、ClassPathBeanDefinitionScanner
   this();
   register(componentClasses);
   refresh();
}

1.1 构造DefaultListableBeanFactory实例

AnnotationConfigApplicationContext继承自GenericApplicationContext，所以会去调用GenericApplicationContext的无参构造方法，而在该无参构造方法中，会实例化一个DefaultListableBeanFactory对象作为beanFactory的实例

// 构造DefaultListableBeanFactory、AnnotatedBeanDefinitionReader、ClassPathBeanDefinitionScanner
public AnnotationConfigApplicationContext() {
   StartupStep createAnnotatedBeanDefReader = this.getApplicationStartup().start("spring.context.annotated-bean-reader.create");
   // 额外会创建StandardEnvironment
   this.reader = new AnnotatedBeanDefinitionReader(this);
   createAnnotatedBeanDefReader.end();
   this.scanner = new ClassPathBeanDefinitionScanner(this);
}

public GenericApplicationContext() {
   this.beanFactory = new DefaultListableBeanFactory();
}

在DefaultListableBeanFactory的无参构造方法中，会调用父类AbstractAutowireCapableBeanFactory的无参构造方法，在该方法中会设置依赖注入时需要忽略的接口的方法，对于BeanNameAware这些回调接口，都提供了回调的set方法，如果某个实例实现了这些接口，同时又是通过ByType或ByName来进行属性注入的，那么在进行属性注入时，如果没有ignoreDependencyInterface缓存，这些set方法也会被用作解析依赖注入，但当这些接口被加入到ignoreDependencyInterface中，依赖注入时就可以跳过这些方法

同时设置实例化的策略，一般都是Cglib策略

public AbstractAutowireCapableBeanFactory() {
   super();
   ignoreDependencyInterface(BeanNameAware.class);
   ignoreDependencyInterface(BeanFactoryAware.class);
   ignoreDependencyInterface(BeanClassLoaderAware.class);
   if (NativeDetector.inNativeImage()) {
      this.instantiationStrategy = new SimpleInstantiationStrategy();
   }
   else {
      this.instantiationStrategy = new CglibSubclassingInstantiationStrategy();
   }
}

1.2 构造AnnotatedBeanDefinitionReader实例

AnnotatedBeanDefinitionReader实例中主要包含了BeanDefinitionRegistry(注册BeanDefinition)、beanNameGenerator(beanName生成器)以及ConditionEvaluator(解析@Conditional注解)

// 额外会创建StandardEnvironment
this.reader = new AnnotatedBeanDefinitionReader(this);

在调用AnnotatedBeanDefinitionReader的双参构造方法时，会去获取或创建Environment的缓存

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
   this(registry, getOrCreateEnvironment(registry));
}

  • 缓存环境变量

    如果ApplicationContext实现了EnvironmentCapable接口，则调用getEnvironment()方法得到Environment实例对象，否则生成一个StandardEnvironment实例对象

    如果EnvironmentCapable是第一次来Environment获取，那么会去调用createEnvironment()方法，也是实例化一个StandardEnvironment对象

    private static Environment getOrCreateEnvironment(BeanDefinitionRegistry registry) {
   Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
   if (registry instanceof EnvironmentCapable) {
      return ((EnvironmentCapable) registry).getEnvironment();
   }
   return new StandardEnvironment();
}

    StandardEnvironment实例化的时候，会去调用它父类AbstractEnvironment的无参构造方法

    在AbstractEnvironment的单参构造方法中，会去获取操作系统的环境变量和程序的环境变量

    public AbstractEnvironment() {
   this(new MutablePropertySources());
}

    protected AbstractEnvironment(MutablePropertySources propertySources) {
   this.propertySources = propertySources;
   this.propertyResolver = createPropertyResolver(propertySources);
   //获取并缓存操作系统的环境变量以及程序运行的环境变量
   customizePropertySources(propertySources);
}

  • 注册核心BeanDefinition

    AnnotatedBeanDefinitionReader的单参构造方法中调用了如下的构造方法，而在这个构造方法中，创建了用来解析@Conditional注解的的ConditionEvaluator实例对象，同时注册各种配置处理器的BeanDefinition

    public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
   Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
   Assert.notNull(environment, "Environment must not be null");
   this.registry = registry;
   // 用来解析@Conditional注解的
   this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
   // 注册
   AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

    设置当前beanFactory的依赖比较器(依赖注入时会用到)，设置候选Bean的解析器(用于判断某个Bean能不能用于依赖注入)

    同时生成ConfigurationClassPostProcessor、AutowiredAnnotationBeanPostProcessor、CommonAnnotationBeanPostProcessor、PersistenceAnnotationBeanPostProcessor、EventListenerMethodProcessor以及DefaultEventListenerFactory的BeanDefinition

    public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
      BeanDefinitionRegistry registry, @Nullable Object source) {

   DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
   if (beanFactory != null) {

      // 设置beanFactory的OrderComparator为AnnotationAwareOrderComparator
      // 它是一个Comparator，是一个比较器，可以用来进行排序，比如new ArrayList<>().sort(Comparator);
      if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
         beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
      }
      // 用来判断某个Bean能不能用来进行依赖注入
      if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
         beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
      }
   }

   Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);

   // 注册ConfigurationClassPostProcessor类型的BeanDefinition
   if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   // 注册AutowiredAnnotationBeanPostProcessor类型的BeanDefinition
   if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   // 注册CommonAnnotationBeanPostProcessor类型的BeanDefinition
   // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
   if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   // 注册PersistenceAnnotationBeanPostProcessor类型的BeanDefinition
   // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
   if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition();
      try {
         def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
               AnnotationConfigUtils.class.getClassLoader()));
      }
      catch (ClassNotFoundException ex) {
         throw new IllegalStateException(
               "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
      }
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   // 注册EventListenerMethodProcessor类型的BeanDefinition，用来处理@EventListener注解的
   if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
   }

   // 注册DefaultEventListenerFactory类型的BeanDefinition，用来处理@EventListener注解的
   if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
   }

   return beanDefs;
}

1.3 构造ClassPathBeanDefinitionScanner实例

在创建扫描器的时候，会调用它的多参构造方法

this.scanner = new ClassPathBeanDefinitionScanner(this);

Spring在启动的过程中，会使用默认的includeFilter，所以会通过registerDefaultFilters()来设置默认的includeFilter

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
      Environment environment, @Nullable ResourceLoader resourceLoader) {

   Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
   this.registry = registry;

   if (useDefaultFilters) {
      registerDefaultFilters();
   }
   setEnvironment(environment);
   setResourceLoader(resourceLoader);
}

includeFilters存放的是包含注解类型，也就是说一个Class类上的注解类型，在includeFilters中有，才会去把类解析成一个BeanDefinition，除了Spring提供的Component类型注解，还支持JDK自带的ManagedBean和Named注解

protected void registerDefaultFilters() {

   // 注册@Component对应的AnnotationTypeFilter
   this.includeFilters.add(new AnnotationTypeFilter(Component.class));

   ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();

   try {
      this.includeFilters.add(new AnnotationTypeFilter(
            ((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
      logger.trace("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
   }
   catch (ClassNotFoundException ex) {
      // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
   }

   try {
      this.includeFilters.add(new AnnotationTypeFilter(
            ((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
      logger.trace("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
   }
   catch (ClassNotFoundException ex) {
      // JSR-330 API not available - simply skip.
   }
}

二、注册配置类

完成构造方法的一些初始化工作之后，会将传入的配置类进行注册

会去调用BeanDefinitionReader的doRegisterBean()完成配置类的注册，解析配置类上的注解，生成一个BeanDefinition

private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
                                @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
                                @Nullable BeanDefinitionCustomizer[] customizers) {

    AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
    if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
        return;
    }

    abd.setInstanceSupplier(supplier);
    // 解析@Scope注解的结果为ScopeMetadata
    ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
    abd.setScope(scopeMetadata.getScopeName());
    String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));

    AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
    if (qualifiers != null) {
        for (Class<? extends Annotation> qualifier : qualifiers) {
            if (Primary.class == qualifier) {
                abd.setPrimary(true);
            }
            else if (Lazy.class == qualifier) {
                abd.setLazyInit(true);
            }
            else {
                abd.addQualifier(new AutowireCandidateQualifier(qualifier));
            }
        }
    }
    if (customizers != null) {
        for (BeanDefinitionCustomizer customizer : customizers) {
            customizer.customize(abd);
        }
    }

    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
    definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
    BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

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