Spring启动流程
spring启动是建立在servlet容器上的，web工程的初始都是在web.xml
<!-- Spring资源上下文定义，在指定地址找到Spring的xml配置文件 -->
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath*:/spring-context*.xml</param-value>
</context-param>
<!-- 1.Spring的上下文监听器 -->
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- 2.SpringMVC的前端控制器 -->
<servlet>
<servlet-name>springServlet</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>
<servlet-mapping>
<servlet-name>springServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
1.Spring的上下文监听器
进入 ContextLoaderListener 可以看到他会去调用 initWebApplicationContext：
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
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!");
}
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 {
// 1.创建WebApplicationContext
if (this.context == null) {
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
if (cwac.getParent() == null) {
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
// 2.加载spring配置文件中的Bean，这里会去扫描配置中contextConfigLocation的路径文件加载
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
// 3.把WebApplicationContext放入ServletContext（Java Web的全局变量）中
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;
}
}
2.SpringMVC的前端控制器
加载 DispatcherServlet 时，根据父类 FrameworkServlet->HttpServletBean->HttpServlet->GenericServlet 的关系，web容器启动会去调用 HttpServletBean 的 init 方法，这个方法覆盖了 GenericServlet 中的 init 方法。
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// 1.如下代码的作用是将Servlet初始化参数设置到该组件上
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
// 2.提供给子类初始化的扩展点，该方法由FrameworkServlet覆盖
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
FrameworkServlet 的 initServletBean内调用 initWebApplicationContext 初始化web上下文，其中核心方法是 onRefresh()
protected WebApplicationContext initWebApplicationContext() {
//ROOT上下文（ContextLoaderListener加载的）
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// 1、在创建该Servlet注入的上下文
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
if (cwac.getParent() == null) {
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
//2、查找已经绑定的上下文
wac = findWebApplicationContext();
}
if (wac == null) {
//3、如果没有找到相应的上下文，并指定父亲为ContextLoaderListener
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
//4、刷新上下文（执行一些初始化）
onRefresh(wac);
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
//省略部分代码
}
return wac;
}
onRefresh() 提供一些前端控制器相关的配置
public class DispatcherServlet extends FrameworkServlet {
//实现子类的onRefresh()方法，该方法委托为initStrategies()方法。
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
//初始化默认的Spring Web MVC框架使用的策略（如HandlerMapping）
protected viod initStrategies(ApplicationContext context){
initMultipartResolver(context);//初始化上传文件解析器
initLocaleResolver(context);//初始化本地解析器
initThemeResolver(context);//初始化主题解析器
initHandlerMapping(context);
//初始化处理器映射器,将请求映射到处理器
initHandlerAdapters(context);//初始化处理器适配器
initHandlerExceptionResolver(context);
//初始化处理器异常解析器,如果执行过程中遇到异常将交给HandlerExceptionResolver来解析
initRequestToViewNameTranslator(context);
//初始化请求到具体视图名称解析器
initViewResolvers(context);
//初始化视图解析器,通过ViewResolver解析逻辑视图名到具体视图实现
initFlshMapManager(context);//初始化flash映射管理
}
}
