容器概述
控制反转（IoC）也称为依赖注入（DI），它是一个过程。对象（Bean）通过构造方法、工厂方法、属性设置依赖项，然后容器在创建对象（Bean）时，注入这些依赖项。此过程从根本上说是通过设置的依赖项去查找对象（Bean）而不是我们主动去设置（因此称为控制翻转）。
IOC概述.png
IOC容器
BeanFactory
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org.springframework.beans中默认实现DefaultListableBeanFactory类图
DefaultListableBeanFactory类图.png
ApplicationContext
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类图
ApplicationContext类图.png
Environment
-
来看下servlet的环境StandardServletEnvironment类图
StandardServletEnvironment类图.png
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Environment是在初始化时AbstractEnvironment调用钩子方法customizePropertySources把对应环境加进去的，下面我们来看下相应的代码
- AbstractEnvironment
public abstract class AbstractEnvironment implements ConfigurableEnvironment {
......
/**
* Create a new {@code Environment} instance, calling back to
* {@link #customizePropertySources(MutablePropertySources)} during construction to
* allow subclasses to contribute or manipulate {@link PropertySource} instances as
* appropriate.
* @see #customizePropertySources(MutablePropertySources)
*/
public AbstractEnvironment() {
//初始化时，子类添加环境
customizePropertySources(this.propertySources);
}
protected void customizePropertySources(MutablePropertySources propertySources) {
//空方法，子类需要添加环境时覆盖
}
......
}
- StandardEnvironment
public class StandardEnvironment extends AbstractEnvironment {
/** System environment property source name: {@value}. */
public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";
/** JVM system properties property source name: {@value}. */
public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";
/**
* Customize the set of property sources with those appropriate for any standard
* Java environment:
* <ul>
* <li>{@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME}
* <li>{@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}
* </ul>
* <p>Properties present in {@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME} will
* take precedence over those in {@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}.
* @see AbstractEnvironment#customizePropertySources(MutablePropertySources)
* @see #getSystemProperties()
* @see #getSystemEnvironment()
*/
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
//添加JVM 环境变量，我们平时在idea和tomcat里面写的-D参数
propertySources.addLast(
new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
//电脑的环境变量
propertySources.addLast(
new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}
}
- StandardServletEnvironment
public class StandardServletEnvironment extends StandardEnvironment implements ConfigurableWebEnvironment {
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
......
// 添加servletConfigInitParams环境，web.xml里面写的init-param
propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
// 添加servletContextInitParams环境，web.xml里面写的context-param
propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
// 添加jndiProperties环境,配置数据库的，一般写在tomcat里面的resource
if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));
}
//调用父类，添加标准环境
super.customizePropertySources(propertySources);
}
......
}
统一资源加载策略
Resource
Java自带的java.net.URL类不足以满足所有对低级资源的访问，比如没有标准化的URL实现可用于访问需要从类路径或相对于ServletContext获得的资源。Spring的Resource接口旨在成为一种功能更强大的接口，用于抽象化对低级资源的访问。下面来看下几个常用resource的类图
resource类图.png
ResourceLoader
ResourceLoader类图.png
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返回多个资源的ResourcePatternResolver
ResourcePatternResolver类图.png
ApplicationContext分析
ClassPathXmlApplicationContext时序图
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加载BeanDefinition时序图
xml加载BeanDefinition.png
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实例化时序图
实例会.png
AbstractApplicationContext的refresh方法
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// 装备刷新方法，时间、环境、事件这些
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 告诉子类刷新BeanFactory,加载BeanDefinition，获取最新的BeanFactory
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 准备BeanFactory，类加载器、忽略接口、属性解析等
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 为某些子类预留的BeanFactory后置处理
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 执行BeanFactoryPostProcessor后置处理
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 注册扫描到的BeanPostProcessor到应用上下文
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();
// Instantiate all remaining (non-lazy-init) singletons.
// 初始化所有剩余的单例bean
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();
}
}
}
ApplicationContext扩展点
FactoryBean
FactoryBean是实现了org.springframework.beans.factory.FactoryBean<T>接口的Bean,从ApplicationContext的getBean()方法获取的对象不是该类的一个实例，而是该类的getObject()方法所返回的对象。
当我们需要获取FactoryBean实例本身而不是它所产生的bean，则要使用'&'符号。
当有复杂的初始化场景，比如返回propertySource、mybatis的代理类
BeanFactoryPostProcess
当BeanFactory加载完成BeanDefinition之后，对BeanDefinition的后置处理
BeanPostProcess
当对象new出来，在执行init方法之前和之后执行
public interface BeanPostProcessor {
// init方法之前
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
// init方式之后
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}
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