- Spring设计理念
Spring这个一站式轻量级开源框架之所以流行,因为该框架把对象之间的依赖关系转而用配置文件管理,也就是 DI依
赖注入机制;而这个注入关系在IoC的容器中被管理,所谓IoC,被称为Inversion of Control,控制反转。指将对象的创建
权反转(交给)给Spring管理来实现程序的解耦。在Spring中核心组件有三个:Core、Context、Bean:
在一场演出中,Bean好比是一个个的演员;Context就是其中的舞台背景;而Core就是演出需要的道具;只有这些拼
凑在一起才能使一场演出顺利进行。
Context就是多个Bean关系的集合,也被称之为IoC容器,Core便作为用来 发现、建立、维护工具每个Bean之间的关
系所需要的一系列工具。
- Bean组件
Bean组件位于 org.springframework.beans包下,该包下的所有类主要涉及 Bean的定义、Bean的创建、Bean的解
析。
Bean的创建是典型的工厂模式,BeanFactory作为顶级接口,有3个子类:ListableBeanFactory接口(表示这些
Bean是可列表的)、HierarchicalBeanFactory接口(表示这些Bean存在继承关系,有父Bean)、以及定义Bean的自
动装配规则的AutowireCapableBeanFactory接口;而最终的默认实现类为DefaultListableBeanFactory。
Bean的定义由BeanDefinition描述,当Spring成功解析定义的<bean />节点后,在Spring内部将转化为
BeanDefinition,此后的操作都将针对该对象进行。
Bean的解析主要是对Spring中配置文件的解析。
- Context组件
Context组件位于 org.springframework.context包下,ApplicationContext作为顶级接口,分别继承了BeanFactory的
子类及 ResourceLoader的子类,使其能够以Bean为运行主体,同时可访问到任何外部资源:
ApplicationContext子类主要包含:ConfigurableApplicationContext及WebApplicationContext,前者用来动态添加
或修改已有配置信息,后者是为Web而准备的Context:
- Core组件
该组件一个重要的组成部分就是利用Resource接口定义了资源的访问方式,如下:
Resource继承了InputStreamSource接口,在该接口中有个getInputStream方法,返回InputStream类,屏蔽了资源
的提供者; ResourceLoader接口屏蔽了资源加载者所带来的差异。
- IoC 控制反转
IoC容器实际上就是Context组件结合其他两个组件共同构建的一个Bean关系网,而构建的入口就是
AbstractApplicationContext中的refresh方法:
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// 1.刷新所有BeanFactory子容器.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 创建BeanFactory后,添加一些Spring本身需要的工具类
prepareBeanFactory(beanFactory);
try {
// 功能扩展性-对已经构建的BeanFactory配置做一些修改
postProcessBeanFactory(beanFactory);
invokeBeanFactoryPostProcessors(beanFactory);
// 功能扩展性-可再创建的Bean实例对象时添加一些自定义操作
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// 2.在BeanFactory进行Bean的实例化及Bean关系网的构建
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
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();
}
}
}
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
/**
* Finish the initialization of this context's bean factory,
* initializing all remaining singleton beans.
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
... ...
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
1. 根据可更新子类AbstractRefreshableApplicationContext中的refreshBeanFactory方法刷新所有BeanFactory子容
器,已存在BeanFactory则更新,否则新创建:
/**
* This implementation performs an actual refresh of this context's underlying
* bean factory, shutting down the previous bean factory (if any) and
* initializing a fresh bean factory for the next phase of the context's lifecycle.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
//将加载、解析Bean的定义
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
2. 利用FactoryBean来进行Bean实例化:
@Override
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
smartSingleton.afterSingletonsInstantiated();
return null;
}
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
接口FactoryBean,是个工厂Bean,可以产生Bean实例的Bean,如果一个类继承或实现FactoryBean,则可以通过实
现getObject方法来自定义扩展Bean实例对象;Spring获取FactoryBean本身的对象可以通过在前面加上&来完成。
详情可以参考:BeanFactory与FactoryBean的比较
- IoC容器的扩展点
1. org.springframework.beans.factory.config.BeanFactoryPostProcessor接口:构建BeanFactory时调用
2. org.springframework.beans.factory.config.BeanPostProcessor接口:构建Bean对象时调用
3. org.springframework.beans.factory.InitializingBean接口:Bean实例被创建时调用
4. org.springframework.beans.factory.DisposableBean接口:Bean实例被销毁时调用
5. org.springframework.beans.factory.FactoryBean接口:可以产生自定义Bean实例的Bean
举例说明:若将IoC容器比作是一个箱子,箱子里有若干球模子,依据模子可造不同的球;还有一个可生产球模子的机
器,以及一个不是预先定型并且形状任意确定的神奇球模;关系如下:
- Spring AOP
未完待续。。。。