Spring框架的引入配置：
web.xml文件：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="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"
version="2.5">
<!-- spring -->
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
classpath*:/applicationContext.xml
</param-value>
</context-param>
<context-param>
<param-name>spring.profiles.default</param-name>
<param-value>production</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
</web-app>web.xml中context-param,listener,filter和servlet的加载顺序：context-param -> listener -> filter -> servlet。
项目启动时，自动加载org.springframework.web.context.ContextLoaderListener
package org.springframework.web.context;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
public ContextLoaderListener() {
}
public ContextLoaderListener(WebApplicationContext context) {
super(context);
}
/**
* Initialize the root web application context.
*/
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
/**
* Close the root web application context.
*/
@Override
public void contextDestroyed(ServletContextEvent event) {
closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
}
由此可知，作为Listener，ContextLoaderListener在容器启动时，会执行contextInitialized方法，在该方法中会调用父类ContextLoader中的initWebApplicationContext(ServletContext servletContext)方法，该方法完成Spring context的初始化工作。
initWebApplicationContext的具体代码如下：
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
//核实是否重复初始化Spring application context
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!");
}
//记录spring context初始化日志
Log logger = LogFactory.getLog(ContextLoader.class);
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
//记录初始化启动开始时间
long startTime = System.currentTimeMillis();
try {
// 初始化并存储context到类成员变量中
if (this.context == null) {
this.context = createWebApplicationContext(servletContext);
}
// 判断是否为ConfigurableWebApplicationContext的实例，
// 这个必然是了，因为上一步返回的实例就是ConfigurableWebApplicationContext类型的了
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// 如果isActive()为fault，则代表该context的内容还没有进行初始化
// 则需要开始进行初始化，动作包括初始化parent context， 设置application context id等
if (cwac.getParent() == null) {
// 初始化parentContext， parentContext为多个web应用共享的applicationContext,在web.xml中默认的参数为parentContextKey
// 仅当parentContext为空的时候才进行parentContext的初始化,也就是说多个web应用配置了parentContextKey,只有第一个被加载的才会生效
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
// 初始化webApplicationContext,该处的cwac为org.springframework.web.context.support.XmlWebApplicationContext
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
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 ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
catch (Error err) {
logger.error("Context initialization failed", err);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
throw err;
}
}查看该方法的源码：
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
// 设置WebApplicationContext的ID
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
wac.setServletContext(sc);
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
//模板模式开始进行WebApplicationContext的初始化，具体实现类为org.springframework.context.support.AbstractApplicationContext
wac.refresh();
}在这个方法中的最后一行代码：wac.refresh();为核心代码，由 org.springframework.context.support. AbstractApplicationContext实现，源码为：
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 设置初始化标识，初始化部分参数
prepareRefresh();
// 销毁原有beanFactory，生成新的beanFactory
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 开始为新的beanFactory进行初始化，注册各种工具类
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
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();
}
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();
}
}
}到此为止，Spring的容器初始化就完成了。refresh()中的各个环节即是Spring在容器进行初始化时需要进行的动作，后面的博客内容中会一一学习讲解，有错误之处还请各位指正，谢谢。