深入浅出Spring源码之IOC（一）
目录
深入浅出Spring源码之IOC
前置知识
AnnotationConfigApplicationContext
register()注册配置类
refresh()刷新IOC容器
前置知识
IOC是Spring最核心部分，IOC即Inversion of Control，意为控制反转，其为创建和提供bean的容器，让程序编写人员把这部分的创建和获取bean对象的工作交给了Spring。先看一个需要了解的概念：BeanDefinition，顾名思义，它是一个定义bean的类。如果把bean看成是一辆汽车，那BeanDefinition就是汽车设计图纸。Spring会根据BeanDefinition来创建bean。
then：
- BeanDefinitionRegistryPostProcessor：向容器注册BeanDefinition的接口。
- BeanFactoryPostProcessor：扩展BeanDefinition的接口。
- BeanPostProcessor：在创建bean的过程中调用的一系列接口。
AnnotationConfigApplicationContext是继承自BeanFactory，是基于注解的Spring的应用上下文。现在的我们已经逐渐抛弃了基于xml的开发方式。
AnnotationConfigApplicationContext
下面从AnnotationConfigApplicationContext的入口开始进入IOC的加载流程：
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
执行构造方法：
public AnnotationConfigApplicationContext() {
/**
* 创建一个读取注解的Bean定义读取器
*
* 完成了spring内部BeanDefinition的注册（主要是后置处理器）
*/
this.reader = new AnnotatedBeanDefinitionReader(this);
/**
* 创建BeanDefinition扫描器
* 可以用来扫描包或者类，继而转换为BeanDefinition
*
* spring默认的扫描包不是这个scanner对象
* 而是自己new的一个ClassPathBeanDefinitionScanner
* spring在执行工程后置处理器ConfigurationClassPostProcessor时，去扫描包时会new一个ClassPathBeanDefinitionScanner
*
* 这里的scanner仅仅是为了程序员可以手动调用AnnotationConfigApplicationContext对象的scan方法
*
*/
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
new AnnotatedBeanDefinitionReader(this)：
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;
//ConditionEvaluator用来处理条件配置 @Conditional
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
//这里注册一些内置的后置处理器
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry)：
public static void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
registerAnnotationConfigProcessors(registry, null);
}
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
//注册了实现Order接口的排序器
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
//设置@AutoWired的候选的解析器：ContextAnnotationAutowireCandidateResolver
// getLazyResolutionProxyIfNecessary方法，它也是唯一实现。
//如果字段上带有@Lazy注解，表示进行懒加载 Spring不会立即创建注入属性的实例，而是生成代理对象，来代替实例
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
/**
* 为我们容器中注册了解析我们配置类的后置处理器ConfigurationClassPostProcessor
* 名字叫:org.springframework.context.annotation.internalConfigurationAnnotationProcessor
*/
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));
}
/**
* 为我们容器中注册了处理@Autowired 注解的处理器AutowiredAnnotationBeanPostProcessor
* 名字叫:org.springframework.context.annotation.internalAutowiredAnnotationProcessor
*/
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));
}
/**
* 为我们容器中注册处理@Required属性的注解处理器RequiredAnnotationBeanPostProcessor
* 名字叫:org.springframework.context.annotation.internalRequiredAnnotationProcessor
*/
if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
/**
* 为我们容器注册处理JSR规范的注解处理器CommonAnnotationBeanPostProcessor
* org.springframework.context.annotation.internalCommonAnnotationProcessor
*/
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));
}
/**
* 处理jpa注解的处理器org.springframework.orm.jpa.support.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));
}
/**
* 处理监听方法的注解@EventListener解析器EventListenerMethodProcessor
*/
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));
}
/**
* 注册事件监听器工厂
*/
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;
}
register()注册配置类
接下来，注册配置类的beanDefinition，ctx.register(Class<?>... annotatedClasses)：
public void register(Class<?>... annotatedClasses) {
Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
this.reader.register(annotatedClasses);
}
public void register(Class<?>... annotatedClasses) {
for (Class<?> annotatedClass : annotatedClasses) {
registerBean(annotatedClass);
}
}
public void registerBean(Class<?> annotatedClass) {
doRegisterBean(annotatedClass, null, null, null);
}
这是一系列调用链，最后会进入doRegisterBean(annotatedClass, null, null, null)：
<T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
@Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
//存储@Configuration注解注释的类
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
//判断是否需要跳过注解，spring中有一个@Condition注解，当不满足条件，这个bean就不会被解析
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
abd.setInstanceSupplier(instanceSupplier);
//解析bean的作用域，如果没有设置的话，默认为单例
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
abd.setScope(scopeMetadata.getScopeName());
//获得beanName
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
//解析通用注解，填充到AnnotatedGenericBeanDefinition，解析的注解为Lazy，Primary，DependsOn，Role，Description
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));
}
}
}
for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
customizer.customize(abd);
}
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
//设置bean的代理模式，这里可指定cglib代理
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
//注册，最终会调用DefaultListableBeanFactory中的registerBeanDefinition方法去注册，
//DefaultListableBeanFactory维护着一系列信息，比如beanDefinitionNames，beanDefinitionMap
//beanDefinitionNames是一个List<String>,用来保存beanName
//beanDefinitionMap是一个Map,用来保存beanName和beanDefinition
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}
refresh()刷新IOC容器
接下来，刷新IOC容器，这里会创建一系列的bean并放入IOC容器ctx.refresh()：
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//准备刷新上下文环境
prepareRefresh();
//获取告诉子类初始化Bean工厂 不同工厂不同实现
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//对bean工厂进行填充属性
prepareBeanFactory(beanFactory);
try {
// 留个子类去实现该接口
postProcessBeanFactory(beanFactory);
// 调用我们的bean工厂的后置处理器，会在此将class扫描成beanDefinition 2.bean工厂的后置处理器调用
invokeBeanFactoryPostProcessors(beanFactory);
// 注册我们bean的后置处理器
registerBeanPostProcessors(beanFactory);
// 初始化国际化资源处理器.
initMessageSource();
// 创建事件多播器
initApplicationEventMulticaster();
// 这个方法同样也是留个子类实现的springboot也是从这个方法进行启动tomcat的.
onRefresh();
//把我们的事件监听器注册到多播器上
registerListeners();
// 实例化我们剩余的单实例bean.
finishBeanFactoryInitialization(beanFactory);
// 最后容器刷新 发布刷新事件(Spring cloud也是从这里启动的)
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
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