Spring及SpringMVC初始化源码分析

首先SpringServletContainerInitializer会执行onStartup()方法（SpringServletContainerInitializer是实现ServletContainerInitializer接口且实现了Servlet3.0的@HandlesTypes(WebApplicationInitializer.class)）。

执行onStartup时，会把实现WebApplicationInitializer的接口按Set集合传入方法中。方法中会把符合判断的类加入到集合中。如果集合不为空，会执行WebApplicationInitializer.onStartup()方法，这里执行的是WebApplicationInitializer的实现类AbstractDispatcherServletInitializer的onStartup()，AbstractDispatcherServletInitializer中执行父类onStartup()方法。代码如下:

SpringServletContainerInitializer类

[code]public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {

List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();

if (webAppInitializerClasses != null) {
for (Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says...
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
initializers.add((WebApplicationInitializer) waiClass.newInstance());
}
catch (Throwable ex) {
throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
}
}
}
}

if (initializers.isEmpty()) {
servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
return;
}

servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
for (WebApplicationInitializer initializer : initializers) {
//执行AbstractDispatcherServletInitializer的onStartup
initializer.onStartup(servletContext);
}
}

AbstractDispatcherServletInitializer类

[code]public void onStartup(ServletContext servletContext) throws ServletException {
//调用父类方法
super.onStartup(servletContext);
//初始化SpringMVC容器并封装到FrameworkServlet中。
registerDispatcherServlet(servletContext);
}
protected void registerDispatcherServlet(ServletContext servletContext) {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return empty or null");

WebApplicationContext servletAppContext = createServletApplicationContext();
Assert.notNull(servletAppContext,
"createServletApplicationContext() did not return an application " +
"context for servlet [" + servletName + "]");
//封装到WebApplicationContext
FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());

ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
Assert.notNull(registration,
"Failed to register servlet with name '" + servletName + "'." +
"Check if there is another servlet registered under the same name.");

registration.setLoadOnStartup(1);
registration.addMapping(getServletMappings());
registration.setAsyncSupported(isAsyncSupported());

Filter[] filters = getServletFilters();
if (!ObjectUtils.isEmpty(filters)) {
for (Filter filter : filters) {
registerServletFilter(servletContext, filter);
}
}

customizeRegistration(registration);
}

AbstractContextLoaderInitializer类

[code]public void onStartup(ServletContext servletContext) throws ServletException {
//初始化Spring容器
registerContextLoaderListener(servletContext);
}

在AbstractContextLoaderInitializer中，方法registerContextLoaderListener(ServletContext servletContext)会创建Spring的容器WebApplicationContext并封装到ContextLoader中。然后在ServletContext中注册监听器ContextLoaderListener。

AbstractContextLoaderInitializer类

[code]protected void registerContextLoaderListener(ServletContext servletContext) {
//初始化Spring的容器
WebApplicationContext rootAppContext = createRootApplicationContext();
if (rootAppContext != null) {
//把Spring的容器封装到ContextLoader中。
ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
listener.setContextInitializers(getRootApplicationContextInitializers());
在ServletContext中注册ContextLoaderListener监听器
servletContext.addListener(listener);
}
else {
logger.debug("No ContextLoaderListener registered, as " +
"createRootApplicationContext() did not return an application context");
}
}

然后继续执行AbstractDispatcherServletInitializer中的registerDispatcherServlet(ServletContext servletContext)方法。代码如下：

AbstractDispatcherServletInitializer类

[code]public void onStartup(ServletContext servletContext) throws ServletException {
super.onStartup(servletContext);
//初始化SpringMVC容器并封装到FrameworkServlet中。
registerDispatcherServlet(servletContext);
}
protected void registerDispatcherServlet(ServletContext servletContext) {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return empty or null");
//初始化SpringMVC容器并
WebApplicationContext servletAppContext = createServletApplicationContext();
Assert.notNull(servletAppContext,
"createServletApplicationContext() did not return an application " +
"context for servlet [" + servletName + "]");
//封装WebApplicationContext到FrameworkServlet中。
FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());

ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
Assert.notNull(registration,
"Failed to register servlet with name '" + servletName + "'." +
"Check if there is another servlet registered under the same name.");

registration.setLoadOnStartup(1);
registration.addMapping(getServletMappings());
registration.setAsyncSupported(isAsyncSupported());

Filter[] filters = getServletFilters();
if (!ObjectUtils.isEmpty(filters)) {
for (Filter filter : filters) {
registerServletFilter(servletContext, filter);
}
}

customizeRegistration(registration);
}

在registerDispatcherServlet(ServletContext servletContext)方法中创建SpringMVC的容器servletAppContext并把些容器封装到FrameworkServlet类中。方便后继在SpringMVC中使用。

Servlet容器启动时，会初始化ContextLoaderListener监听器的contextInitialized()方法。contextInitialized()方法中会取得ServletContextEvent事件并调用父类ContextLoader中的initWebApplicationContext()方法。在类中configureAndRefreshWebApplicationContext()方法会刷新容器。最后把Spring的容器WebApplicationContext保存到ServletContext及本地缓存中（currentContextPerThread）。代码如下:

ContextLoaderListener类

[code]public void contextInitialized(ServletContextEvent event) {
//执行父类中的initWebApplicationContext
initWebApplicationContext(event.getServletContext());
}

ContextLoader类

[code]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 {
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
if (this.context == null) {
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
//刷新容器，初始化Spring中的所有的Bean
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
//ServletContext保存Spring容器WebApplicationContext.
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) {
//保存到本地缓存
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;
}
}

初始化SpringMVC
Servlet容器会执行HttpServletBean(DispatcherServlet的父类，HttpServlet的子类)的初始化init()方法。在init()方法中会调用initServletBean()（在HttpServletBean子类FrameworkServlet类中实现）方法。在initServletBean()方法中有一个重要的方法initWebApplicationContext(),此方法是设置Spring容器和SpringMVC容器父子关系的重要方法。在此方法中，会在ServletContext中取出Spring容器把它设置为SpringMVC的父容器。最后刷新SpringMVC容器。代码如下:

HttpServletBean类

[code]public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}

// Set bean properties from init parameters.
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;
}
}

// Let subclasses do whatever initialization they like.
//调用子类FrameworkServlet中的initServletBean()方法
initServletBean();

if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}

FrameworkServlet类

[code]protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();

try {
//设置Spring容器为SpringMVC的父容器
this.webAp
1b5d8
plicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
catch (RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}

if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}

protected WebApplicationContext initWebApplicationContext() {
//在ServletContext中取出Spring容器
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;

if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
//SpringMVC容器，
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
//设置Spring容器为SpringMVC容器的父容器
cwac.setParent(rootContext);
}
//刷新SpringMVC容器，初始化SpringMVC容器的Bean
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}

if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
//初始化DispatcherServlet中的各种Bean，设置各种配置，为后继的请求所用。
onRefresh(wac);
}

if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}

return wac;
}

DispatcherServlet类

[code]protected void onRefresh(ApplicationContext context) {
//初始化DispatcherServlet中的各种Bean，设置各种配置，为后继的请求所用。
initStrategies(context);
}

protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}

以上为Spring,SpringMVC初始化的流程及相关代码。