IOC容器介绍
Spring 通过一个配置文件描述 Bean 及 Bean 之间的依赖关系，利用 Java 语言的反射功能实例化 Bean 并建立 Bean 之间的依赖关系。 Spring 的 IoC 容器在完成这些底层工作的基础上，还提供了 Bean 实例缓存、生命周期管理、 Bean 实例代理、事件发布、资源装载等高级服务。
- BeanFactory 是 Spring 框架的基础设施，面向 Spring 本身；
- ApplicationContext 面向使用 Spring 框架的开发者，几乎所有的应用场合我们都直接使用 ApplicationContext 而非底层的 BeanFactory。
IOC容器的创建过程
查看Spring启动时IOC容器初始化源码
- 在resource目录下新建一个xml文件
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="a" class="com.zh.source.A"></bean>
<bean id="b" class="com.zh.source.B"></bean>
</beans>
- 在src的下面新建了两个类A,B
public class A {
}
public class B {
}
- 在src下面新建一个测试类
public class TestSpring {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("test.xml");
System.out.println(context.getBean("a"));
}
}
- debug启动查看源码
//ClassPathXmlApplicationContext类
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
// 由上面方法调用
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
// 1. 调用父类，资源路径匹配
super(parent);
// 2. 解析配置文件，configLocations就是读到的xml配置文件
setConfigLocations(configLocations);
if (refresh) {
//3.
refresh();
}
}
- setConfigLocations
//2 AbstractRefreshableConfigApplicationContext类
public void setConfigLocations(@Nullable String... locations) {
// 如果读取到的配置文件不为空，则进行下一步处理
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
// 将读取到了配置文件遍历赋值给configLocations
for (int i = 0; i < locations.length; i++) {
// 2.1
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
// 2.1
protected String resolvePath(String path) {
// 2.2 getEnvironment()：获取环境变量等
//resolveRequiredPlaceholders(path) 将配置文件中变量做一个替换
return getEnvironment().resolveRequiredPlaceholders(path);
}
2.2 getEnvironment
// 2.2 AbstractApplicationContext, 获取环境变量等
public ConfigurableEnvironment getEnvironment() {
if (this.environment == null) {
// 2.3
this.environment = createEnvironment();
}
return this.environment;
}
// 2.3 查询环境变量，
protected ConfigurableEnvironment createEnvironment() {
return new StandardEnvironment();
}
3 refresh
// 3 AbstractApplicationContext
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
// 3.1 为刷新准备这个上下文
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 3.2 创建Bean工厂
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 3.3 准备在此上下文中使用的bean工厂
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// BeanFactory的增强器扩展接口
postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
// 3.4 调用在上下文中注册的bean的工厂处理器（增强器）
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 注册Bean的处理器（增强器）
registerBeanPostProcessors(beanFactory);
beanPostProcess.end();
// Initialize message source for this context.
// 国际化配置
initMessageSource();
// Initialize event multicaster for this context.
// 初始化应用程序事件（广播器（观察者模式））
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 扩展方法：初始化特定上下文子类中的其他特殊bean
onRefresh();
// Check for listener beans and register them.
// 注册事件
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 实例化所有剩余的(非懒加载)单例
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 最后一步:发布相应的事件
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();
contextRefresh.end();
}
}
}
3.1 prepareRefresh
// 3.1 AbstractApplicationContext类，该方法主要是为刷新上下文做准备
protected void prepareRefresh() {
// Switch to active.
this.startupDate = System.currentTimeMillis(); // 获取当前时间
this.closed.set(false); // 设置默认值
this.active.set(true); // 设置默认值
// 日志的打印
if (logger.isDebugEnabled()) {
if (logger.isTraceEnabled()) {
logger.trace("Refreshing " + this);
}
else {
logger.debug("Refreshing " + getDisplayName());
}
}
// Initialize any placeholder property sources in the context environment.
// 扩展方法
initPropertySources();
// Validate that all properties marked as required are resolvable:
// see ConfigurablePropertyResolver#setRequiredProperties
// getEnvironment(): 如果有当前环境变量就直接使用，没有的话就创建一个StandardEnvironment()
// validateRequiredProperties(): 对属性做基本的验证
getEnvironment().validateRequiredProperties();
// Store pre-refresh ApplicationListeners...
// 创建存储监听器的集合
if (this.earlyApplicationListeners == null) {
this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
}
else {
// Reset local application listeners to pre-refresh state.
this.applicationListeners.clear();
this.applicationListeners.addAll(this.earlyApplicationListeners);
}
// Allow for the collection of early ApplicationEvents,
// to be published once the multicaster is available...
this.earlyApplicationEvents = new LinkedHashSet<>();
}
3.2 obtainFreshBeanFactory
// AbstractApplicationContext 类
// 3.2 创建Bean工厂
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
// 3.2.1 刷新BeanFactory
refreshBeanFactory();
// 获取beanFactory,这时候BeanFactory以及创建过了，这里只是判断非空返回
return getBeanFactory();
}
3.2.1 refreshBeanFactory
// AbstractRefreshableApplicationContext类
// 3.2.1 刷新BeanFactory
protected final void refreshBeanFactory() throws BeansException {
// 判断是否以及存在Bean工厂，true:已存在，false: 不存在
if (hasBeanFactory()) {
// 存在Bean工厂了，则销毁Bean工厂
destroyBeans();
closeBeanFactory();
}
try {
// createBeanFactory():创建BeanFactory
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
// 定制化BeanFactory
customizeBeanFactory(beanFactory);
// 3.2.1.1 加载Bean的定义信息
loadBeanDefinitions(beanFactory);
this.beanFactory = beanFactory;
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
// 创建一个DefaultListableBeanFactory，
protected DefaultListableBeanFactory createBeanFactory() {
return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}
注意：loadBeanDefinitions(beanFactory)是一个重点，表示加载bean的定义信息
3.2.1.1 loadBeanDefinitions
// AbstractXmlApplicationContext类，因为用的是xml配置文件，所有进入的是这个类
// 3.2.1.1
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
// 创建一个xmlBean定义信息读取类
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
// 设置环境
beanDefinitionReader.setEnvironment(this.getEnvironment());
// 设置当前处理类
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
// 初始化Bean定义类型
initBeanDefinitionReader(beanDefinitionReader);
// 加载bean定义信息
loadBeanDefinitions(beanDefinitionReader);
}
// 加载bean定义信息
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
// 将配置文件放入数组
Resource[] configResources = getConfigResources();
if (configResources != null) {
// 读取bean定义信息
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
3.3 准备在此上下文中使用的bean工厂
// AbstractApplicationContext类
// 3.3 准备在此上下文中使用的bean工厂
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
// 设置beanFactory的类加载器等参数
beanFactory.setBeanClassLoader(getClassLoader());
if (!shouldIgnoreSpel) {
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
}
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
// 向beanFactory 注入Bean增强器（BeanPostProcessor）
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
beanFactory.ignoreDependencyInterface(ApplicationStartupAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Register early post-processor for detecting inner beans as ApplicationListeners.
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (!NativeDetector.inNativeImage() && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {
beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
}
}
3.4 调用在上下文中注册为bean的工厂处理器（增强器）
// AbstractApplicationContext
// 3.4 调用在上下文中注册为bean的工厂处理器（增强器）
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// getBeanFactoryPostProcessors(): 获取beanFactory的增强器
// invokeBeanFactoryPostProcessors：执行beanFactory的增强器
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
if (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
