Spring IOC基于注解启动分析

Spring 基于注解启动

主要有两个Class实现注解启动

• AnnotationConfigApplicationContext
• AnnotationConfigWebApplicationContext

我们以AnnotationConfigApplicationContext 为研究对象

AnnotationConfigApplicationContext.png

引入Spring 最小依赖

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>

编写器启动代码

 public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
        applicationContext.register(BeanConfig.class);
        applicationContext.refresh();
        Date date = applicationContext.getBean("date",Date.class);
        System.out.println(date);
    }

AnnotationConfigApplicationContext 构造函数

    public AnnotationConfigApplicationContext() {
                //负责注册Class ，读取器
        this.reader = new AnnotatedBeanDefinitionReader(this);
               //负责扫描指定类路径下的Class，注册bean
        this.scanner = new ClassPathBeanDefinitionScanner(this);
    }

AnnotatedBeanDefinitionReader 构造方法

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

    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;
               //初始化ConditionEvaluator
        this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
                 
        /** 在給定的注册表中註冊所有相关的post processors
         *  判断容器是否已经存在给定注册表的bean，如果没有注册bean，并将bean放入容器中
         *  把所有的处理处理器列出来
         * ConfigurationClassPostProcessor 內部管理的配置注解处理器
         * AutowiredAnnotationBeanPostProcessor  内部管理@Autowired 的处理器
         * RequiredAnnotationBeanPostProcessor  @Required的处理器
         * CommonAnnotationBeanPostProcessor  JSR-250注解处理器 ，先判断是否支持jsr，如果支持注册
         * PersistenceAnnotationBeanPostProcessor JPA管理 先使用类加载器查找是否存在，如果有这个包则注册
         * EventListenerMethodProcessor  @EventListener的处理器
         * DefaultEventListenerFactory 管理EventListenerFactory处理器
         */
        AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
    }

ConditionEvaluator 这个对象干什么,点击进去

    public ConditionEvaluator(@Nullable BeanDefinitionRegistry registry,
            @Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {

        this.context = new ConditionContextImpl(registry, environment, resourceLoader); 
    }
        //ConditionContextImpl 实现了ConditionContext接口，ConditionEvaluator静态内部类
        public ConditionContextImpl(@Nullable BeanDefinitionRegistry registry,
                @Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {

            this.registry = registry;
            this.beanFactory = deduceBeanFactory(registry);
            this.environment = (environment != null ? environment : deduceEnvironment(registry));
            this.resourceLoader = (resourceLoader != null ? resourceLoader : deduceResourceLoader(registry));
            this.classLoader = deduceClassLoader(resourceLoader, this.beanFactory);
        }

可以知道ConditionEvaluator使用外部传参的方法初始化了Spring容器顶级对象
BeanFactory,Environment,ResourceLoader,ClassLoader。在将这些传给ConditionContextImpl为接下来的解析@Conditional注解做好准备

ClassPathBeanDefinitionScanner构造函数

    public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) {
        this(registry, true);
    }

    public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {
        this(registry, useDefaultFilters, getOrCreateEnvironment(registry));
    }

    public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
            Environment environment) {
        this(registry, useDefaultFilters, environment,
                (registry instanceof ResourceLoader ? (ResourceLoader) registry : null));
    }

    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);
    }

    protected void registerDefaultFilters() {
        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.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
        }
        catch (ClassNotFoundException ex) {
        }
        try {
            this.includeFilters.add(new AnnotationTypeFilter(
                    ((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
            logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
        }
        catch (ClassNotFoundException ex) {
            // JSR-330 API not available - simply skip.
        }
    }

绕了地球几圈了，其实就是将Spring 顶级接口 Environment,ResourceLoader赋值，使用默认注解过滤器，首先将@Component加入List中，判断当前环境是否支持JSR-250，JSR-330，相应加入过滤器中。也就是这个扫描器默认只扫描@Component或者JSR-250，JSR-330的标记的Class。

applicationContext.register(BeanConfig.class)

    public void register(Class<?>... annotatedClasses) {
        Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
        this.reader.register(annotatedClasses); //调用 刚刚初始化读取器
    }
                                            |
============================AnnotatedBeanDefinitionReader 读取器代码======================================================================================================
       public void register(Class<?>... annotatedClasses) {
        for (Class<?> annotatedClass : annotatedClasses) {
            registerBean(annotatedClass);
        }
     }

    public void registerBean(Class<?> annotatedClass) {
        doRegisterBean(annotatedClass, null, null, null);
    }
        
    /**
    *从给定的bean解析Class给定的注解，执行相应的初始化，保存到Spring容器中
    */
    <T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
            @Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {

        //根据Class的Annotated 得出元数据 AnnotationMetadata
        AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
       /**
        *  判断注册的Class 是否包含@Conditional注解，如果有获取全部value，放入List中
        *  排序后，遍历所有的Conditiion的实现，使用反射获取对象，执行matches方法，
        * 如果发现有返回false，中断循环直接返回true，
        */
        if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) { //如果 @Conditional条件不满足，不进行注册
            return;
        }

        abd.setInstanceSupplier(instanceSupplier);
        //解析Class是否有@Scope,解析@Scope注解返回ScopeMetadata对象，没有直接返回空
        ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
        abd.setScope(scopeMetadata.getScopeName());
       //判断注解上Value是否有值，有就使用这个作为BeanName，没有则取类名 
        String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
        //继续解析AnnotationMetadata的@Lazy,@Primary，@DependsOn，@Role，@Description的注解，放入结果放入对象的属性中
        AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
        //这个类只是BeanDefinition 包装类
        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
        //是否需要代理类，如果是则修改内部属性，重新生成BeanDefinition 对象
        definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
      //调用DefaultListableBeanFactory.registerBeanDefinition的方法，做一些安全性校验再，将definitionHolder  放入register容器中
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
    }

这个方法就是将注册的Bean，解析Class上的注解，初始化注解数据，做相应处理，转化成BeanDefinition ,放入Spring 容器中保存起来。
我们看下BeanDefinition是怎么实现注册到Spring的容器中，主要由DefaultListableBeanFactory.registerBeanDefinition来实现

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                //对beanDefinition 进行校验判断MethodOverrides不能为空，必须拥有工厂方法
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition oldBeanDefinition;

        oldBeanDefinition = this.beanDefinitionMap.get(beanName); 
        if (oldBeanDefinition != null) {
             //这个方法是判断是否允许出现重名bean，并且是不同的定义bean，是否可以覆盖前者
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                        "': There is already [" + oldBeanDefinition + "] bound.");
            }
            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else if (!beanDefinition.equals(oldBeanDefinition)) {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName +
                            "' with a different definition: replacing [" + oldBeanDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Overriding bean definition for bean '" + beanName +
                            "' with an equivalent definition: replacing [" + oldBeanDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }
        else {
            //调用alreadyCreated.isEmpty()，alreadyCreated Set对象，保存已经创建beanName
           //文档中表示created，跟这里注册应该不是同一个行为，这个要看到后面才知道什么意思
            if (hasBeanCreationStarted()) {
                synchronized (this.beanDefinitionMap) {//更新数据
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    if (this.manualSingletonNames.contains(beanName)) {
                        Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
                        updatedSingletons.remove(beanName);
                        this.manualSingletonNames = updatedSingletons;
                    }
                }
            }
            else { 
                //Spring  beanDefinition 容器，一个Map转载
                this.beanDefinitionMap.put(beanName, beanDefinition);
              //保存beanName，主要用于记录每个bean注册顺序
                this.beanDefinitionNames.add(beanName);
              //删除单例，注册成一个普通bean
                this.manualSingletonNames.remove(beanName);
            }
            this.frozenBeanDefinitionNames = null;
        }

        if (oldBeanDefinition != null || containsSingleton(beanName)) { 
            //更新Spring容器里beanName
            resetBeanDefinition(beanName);
        }
    }

将beanDefinition注册到Spring容器中，并没有太多复杂的逻辑，只是做一些安全性的检查。

BeanDefinition

一个BeanDefinition描述了一个bean的实例，包括属性值，构造方法参数值和继承自它的类的更多信息。BeanDefinition仅仅是一个最简单的接口，主要功能是允许BeanFactoryPostProcessor 例如PropertyPlaceHolderConfigure 能够检索并修改属性值和别的bean的元数据（译注）
Spring 容器beanDefinition主要分为RootBeanDefinition,AnnotatedGenericBeanDefinition这两种

• RootBeanDefinition Spring Factory中的特定bean
• AnnotatedGenericBeanDefinition 用户自定义bean

Spring 启动流程总结

AnnotationConfigApplicationContext 初始化.png

这些BeanDefinition只是放入到Spirng 容器中，并没有进行任何初始化对象的操作，真正的IOC操作都在refresh(),这个方法有空再进行分析。