Spring启动原理和可扩展设计分析
简述
spring核心是一个容器，但是却能在它身上像插件一样集成很多功能，在设计上要做到封闭修改、扩展开放，这一点spring做的很优秀，对开发框架有很好的借鉴和指导意义。
本文通过分析spring的启动过程来分析spring扩展开放的设计实现，下面主要集中在两个点来分析：Aware和BeanPostProcessor。spring自身很多扩展功能也都是通过这两个机制来实现。
原则
spring在启动过程中会注册很多回调来实现各种扩展功能，回调的形式最重要的是Aware和BeanPostProcessor。
spring各种不同业务都是一个思路:
- 创建不同的ApplicationContext
- 不同的ApplicationContext写死一个Aware类型的BeanPostProcessor
- 由写死的Aware类型BeanPostProcessor来加载特殊业务的各种逻辑
Aware
每当spring容器完成某件事情(如ApplicationContext初始化完成)时都会通知Aware，Aware通常都具有一些setXXX()的方法，如BeanFactoryAware：
public interface BeanFactoryAware extends Aware { void setBeanFactory(BeanFactory beanFactory) throws BeansException;}BeanPostProcessor
可以对spring扫描到的bean做手脚，初始化前和后
public interface BeanPostProcessor { Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException; Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;}Spring 启动过程
spring容器启动的模板编排在org.springframework.context.support.AbstractApplicationContext#refresh
public void refresh() throws BeansException, IllegalStateException { prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. //子类通常在这里添加自己需要的BeanPostProcessor postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. //查找所有BeanPostProcessor并注册到容器中，bean初始化时会来调用bpp 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. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); }}其中AbstractApplicationContext#prepareBeanFactory里注册ApplicationContext的Aware处理器：
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this))ApplicationContextAwareProcessor里会触发各种aware
- ApplicationContextAware
- ApplicationEventPublisherAware
- ResourceLoaderAware
- EmbeddedValueResolverAware
- EnvironmentAware
实现Aware的各种bean接收到回调后就能获取各自想要的东西(ApplicationContext、ResourceLoader等)，有了这些东西他们就可以实现自己的个性化逻辑
spring web启动
下面以spring web为例看看Spring web是如何在spring的基础上实现扩展的。
spring web的ApplicationContext大多集成自AbstractRefreshableWebApplicationContext
首先，还是那个套路，创建特殊的ApplicationContext，然后写死一个BeanPostProcessor
AbstractRefreshableWebApplicationContext#postProcessBeanFactory
@Override protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) { beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig)); }ServletContextAwareProcessor处理两种类型的Aware
- ServletContextAware
- ServletConfigAware
这是上面说的典型的套路
实现了ServletContextAware的bean就这样获取到了web上下文，可以做自己的事情了
spring web初始化方式
web.xml + ContextLoaderListener
< listener > < listener-class > org.springframework.web.context.ContextLoaderListener listener-class > listener >contextConfigLocationclasspath:conf/spring/applicationContext.xmlContextLoaderListener 初始化WebApplicationContext 判断启动哪种WebApplicationContext
- web.xml 里的context-param找contextClass
- 没有的话就加载默认：spring jar里ContextLoader.properties写的XmlWebApplicationContext
web.mxl + DispatcherServlet
springMvcorg.springframework.web.servlet.DispatcherServletDispatcherServlet基于Servlet生命周期会在javax.servlet.GenericServlet.init()初始化spring容器
springboot
DispatcherServletAutoConfiguration
@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) public DispatcherServlet dispatcherServlet() { DispatcherServlet dispatcherServlet = new DispatcherServlet(); dispatcherServlet.setDispatchOptionsRequest( this.webMvcProperties.isDispatchOptionsRequest()); dispatcherServlet.setDispatchTraceRequest( this.webMvcProperties.isDispatchTraceRequest()); dispatcherServlet.setThrowExceptionIfNoHandlerFound( this.webMvcProperties.isThrowExceptionIfNoHandlerFound()); return dispatcherServlet; }Spring MVC原理
接着上面的web原理
Dispatcher
Dispatcher是一个Servlet，是spring web的入口，来看下spring的dispatcher如何处理请求
spring mvc
Spring MVC的入口是Controller，那么解析Controller的东西自然就是SpringMVC的入口了。
这个入口就是：
RequestMappingHandlerMapping
这个东西继承了3个Aware
- ApplicationAware(Spring web)
- ServletContextAware (Spring web)
- EmbeddedValueResolverAware (Spring context)
是不是很熟悉！
通过Aware，Spring mvc就这么起来了！并且能够自定义解析各种注解
RequestMappingHandlerMapping
内部维护一个Map handlerMethods，T就是Controller的类
public class RequestMappingHandlerMapping extends RequestMappingInfoHandlerMapping implements MatchableHandlerMapping, EmbeddedValueResolverAware { /** 1. 初始化 */ public void afterPropertiesSet() { initHandlerMethods(); } /** 2. 扫描所有Object的bean，扫描Controller、RequestMapping 3. 扫描每个controller的web请求方法，写入到handlerMethods里，以后处理请求时用来对应查找 */ protected void initHandlerMethods() { String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ? BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) : getApplicationContext().getBeanNamesForType(Object.class)); for (String beanName : beanNames) { if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX) && isHandler(getApplicationContext().getType(beanName))){ //查找web请求方法 detectHandlerMethods(beanName); } } handlerMethodsInitialized(getHandlerMethods()); } @Override protected boolean isHandler(Class> beanType) { return ((AnnotationUtils.findAnnotation(beanType, Controller.class) != null) || (AnnotationUtils.findAnnotation(beanType, RequestMapping.class) != null)); } /** 4. 处理web请求时负责找到对应的处理方法 */ @Override public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { Object handler = getHandlerInternal(request); if (handler == null) { handler = getDefaultHandler(); } if (handler == null) { return null; } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } /** 组装HandlerExecutionChain，里面主要包括处理列表： List interceptorList; */ return getHandlerExecutionChain(handler, request); }}
