Spring容器启动源码解析

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:web="http://java.sun.com/xml/ns/javaee" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<display-name>dmpserver</display-name>
<welcome-file-list>
<welcome-file>login.jsp</welcome-file>
</welcome-file-list>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring.xml</param-value>
</context-param>
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>classpath:log4jConfig.xml</param-value>
</context-param> <filter>
<filter-name>encodingFilter</filter-name>
<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<listener>
<listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener>
<servlet>
<description>spring mvc servlet</description>
<servlet-name>rest</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>
classpath:spring-mvc.xml
</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet></web-app>

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
public ContextLoaderListener() {
} public ContextLoaderListener(WebApplicationContext context) {
super(context);
} public void contextInitialized(ServletContextEvent event) {
this.initWebApplicationContext(event.getServletContext());
} public void contextDestroyed(ServletContextEvent event) {
this.closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
}

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
/*
首先通过WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
这个String类型的静态变量获取一个根IoC容器，根IoC容器作为全局变量
存储在application对象中，如果存在则有且只能有一个
如果在初始化根WebApplicationContext即根IoC容器时发现已经存在
则直接抛出异常，因此web.xml中只允许存在一个ContextLoader类或其子类的对象
*/
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
throw new IllegalStateException("Cannot initialize context because there is already a root application context present - check whether you have multiple ContextLoader* definitions in your web.xml!");
} else {
Log logger = LogFactory.getLog(ContextLoader.class);
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
} long startTime = System.currentTimeMillis(); try {
if (this.context == null) {
// 创建一个根IOC容器
this.context = this.createWebApplicationContext(servletContext);
} if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)this.context;
if (!cwac.isActive()) {
if (cwac.getParent() == null) {
// 为根IOC容器设置一个父容器
ApplicationContext parent = this.loadParentContext(servletContext);
cwac.setParent(parent);
} this.configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
//将创建好的IoC容器放入到application对象中，并设置key为WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = this.context;
} else if (ccl != null) {
currentContextPerThread.put(ccl, this.context);
} if (logger.isDebugEnabled()) {
logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
} if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
} return this.context;
} catch (RuntimeException var8) {
logger.error("Context initialization failed", var8);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var8);
throw var8;
} catch (Error var9) {
logger.error("Context initialization failed", var9);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var9);
throw var9;
}
}
}

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
String configLocationParam;
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
configLocationParam = sc.getInitParameter("contextId");
if (configLocationParam != null) {
wac.setId(configLocationParam);
} else {
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath()));
}
} wac.setServletContext(sc);
/*
在容器启动时，会把<context-param>中的内容放入servlet上下文的全局变量中，
此时获取key为contextConfigLocation的变量，及Spring.xml配置文件
将其放入到webApplicationContext中
*/
configLocationParam = sc.getInitParameter("contextConfigLocation");
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
} ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment)env).initPropertySources(sc, (ServletConfig)null);
} this.customizeContext(sc, wac);
wac.refresh();
}

public void refresh() throws BeansException, IllegalStateException {
Object var1 = this.startupShutdownMonitor;
synchronized(this.startupShutdownMonitor) {
this.prepareRefresh();
ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
this.prepareBeanFactory(beanFactory); try {
this.postProcessBeanFactory(beanFactory);
this.invokeBeanFactoryPostProcessors(beanFactory);
this.registerBeanPostProcessors(beanFactory);
this.initMessageSource();
this.initApplicationEventMulticaster();
this.onRefresh();
this.registerListeners();
this.finishBeanFactoryInitialization(beanFactory);
this.finishRefresh();
} catch (BeansException var9) {
if (this.logger.isWarnEnabled()) {
this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
} this.destroyBeans();
this.cancelRefresh(var9);
throw var9;
} finally {
this.resetCommonCaches();
} }
}