前文我们有了IOC的源码基础以及SpringMVC的基础,我们便可以进一步深入理解SpringMVC主要实现原理,包含DispatcherServlet的初始化过程和DispatcherServlet处理请求的过程的源码解析。本文是第一篇:DispatcherServlet的初始化过程的源码解析。@anarkh
- Spring进阶 - SpringMVC实现原理之DispatcherServlet的初始化过程
- DispatcherServlet和ApplicationContext有何关系?
- DispatcherServlet是如何初始化的?
- init
- initWebApplicationContext
- refresh
- initHanlderxxx
DispatcherServlet和ApplicationContext有何关系?
DispatcherServlet 作为一个 Servlet,需要根据 Servlet 规范使用 Java 配置或 web.xml 声明和映射。反过来,DispatcherServlet 使用 Spring 配置来发现请求映射、视图解析、异常处理等等所需的委托组件。那它和ApplicationContext有和关系呢?如下内容可以参考官网-SpringMVC文档在新窗口打开
DispatcherServlet 需要 WebApplicationContext(继承自 ApplicationContext) 来配置。WebApplicationContext 可以链接到ServletContext 和 Servlet。因为绑定了 ServletContext,这样应用程序就可以在需要的时候使用 RequestContextUtils 的静态方法访问 WebApplicationContext。
大多数应用程序只有一个WebApplicationContext,除此之外也可以一个Root WebApplicationContext 被多个 Servlet实例,然后各自拥有自己的Servlet WebApplicationContext 配置。
Root WebApplicationContext 包含需要共享给多个 Servlet 实例的数据源和业务服务基础 Bean。这些 Bean 可以在 Servlet 特定的范围被继承或覆盖。
(PS:官网上的这张图可以可以帮助你构建DispatcherServlet和ApplicationContext在设计上的认知,这一点对于理解DispatcherServlet的设计和初始化过程非常重要)

DispatcherServlet是如何初始化的?
DispatcherServlet首先是Sevlet,Servlet有自己的生命周期的方法(init,destory等),那么我们在看DispatcherServlet初始化时首先需要看源码中DispatcherServlet的类结构设计。
首先我们看DispatcherServlet的类结构关系,在这个类依赖结构中找到init的方法

很容易找到init()的方法位于HttpServletBean中,然后跑Spring基础 - SpringMVC请求流程和案例中的代码,在init方法中打断点。

init
init()方法如下, 主要读取web.xml中servlet参数配置,并将交给子类方法initServletBean()继续初始化
@Override
public final void init() throws ServletException {
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;
}
}
initServletBean();
}读取配置可以从下图看出,正是初始化了我们web.xml中配置

再看下initServletBean()方法,位于FrameworkServlet类中
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
if (logger.isInfoEnabled()) {
logger.info("Initializing Servlet '" + getServletName() + "'");
}
long startTime = System.currentTimeMillis();
try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
if (logger.isDebugEnabled()) {
String value = this.enableLoggingRequestDetails ?
"shown which may lead to unsafe logging of potentially sensitive data" :
"masked to prevent unsafe logging of potentially sensitive data";
logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
"': request parameters and headers will be " + value);
}
if (logger.isInfoEnabled()) {
logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
}
}initWebApplicationContext
initWebApplicationContext用来初始化和刷新WebApplicationContext。
initWebApplicationContext() 方法如下
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
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) {
wac = findWebApplicationContext();
}
if (wac == null) {
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
}
}
if (this.publishContext) {
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}webApplicationContext只会初始化一次,依次尝试构造函数初始化,没有则通过contextAttribute初始化,仍没有则创建新的
创建的createWebApplicationContext方法如下
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
Class<?> contextClass = getContextClass();
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
wac.setParent(parent);
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
configureAndRefreshWebApplicationContext(wac);
return wac;
}configureAndRefreshWebApplicationContext方法初始化设置Spring环境
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
if (this.contextId != null) {
wac.setId(this.contextId);
}
else {
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
}
}
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
wac.refresh();
}refresh
有了webApplicationContext后,就开始刷新了(onRefresh()方法),这个方法是FrameworkServlet提供的模板方法,由子类DispatcherServlet来实现的。
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}刷新主要是调用initStrategies(context)方法对DispatcherServlet中的组件进行初始化,这些组件就是在SpringMVC请求流程中包的主要组件。
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}initHanlderxxx
我们主要看initHandlerXXX相关的方法,它们之间的关系可以看SpringMVC的请求流程:

- HandlerMapping是映射处理器
- HandlerAdpter是处理适配器 ,它用来找到你的Controller中的处理方法
- HandlerExceptionResolver是当遇到处理异常时的异常解析器
initHandlerMapping方法如下,无非就是获取按照优先级排序后的HanlderMappings, 将来匹配时按照优先级最高的HanderMapping进行处理。

initHandlerAdapters方法和initHandlerExceptionResolvers方法也是类似的,如果没有找到,那就构建默认的。
private void initHandlerAdapters(ApplicationContext context) {
this.handlerAdapters = null;
if (this.detectAllHandlerAdapters) {
Map<String, HandlerAdapter> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerAdapters = new ArrayList<>(matchingBeans.values());
AnnotationAwareOrderComparator.sort(this.handlerAdapters);
}
}
else {
try {
HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
this.handlerAdapters = Collections.singletonList(ha);
}
catch (NoSuchBeanDefinitionException ex) {
}
}
if (this.handlerAdapters == null) {
this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
private void initHandlerExceptionResolvers(ApplicationContext context) {
this.handlerExceptionResolvers = null;
if (this.detectAllHandlerExceptionResolvers) {
Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
}
}
else {
try {
HandlerExceptionResolver her =
context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
this.handlerExceptionResolvers = Collections.singletonList(her);
}
catch (NoSuchBeanDefinitionException ex) {
}
}
if (this.handlerExceptionResolvers == null) {
this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}最后我们看下初始化的日志:
21:30:33.163 [RMI TCP Connection(2)-127.0.0.1] INFO org.springframework.web.servlet.DispatcherServlet - Initializing Servlet 'springmvc-demo'
21:30:38.242 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.context.support.XmlWebApplicationContext - Refreshing WebApplicationContext for namespace 'springmvc-demo-servlet'
21:30:39.256 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [/Users/anarkh/anarkh/www/tech-anarkh-spring-demos/011-spring-framework-demo-springmvc/target/011-spring-framework-demo-springmvc-1.0-SNAPSHOT/WEB-INF/classes/tech/anarkh/springframework/springmvc/controller/UserController.class]
21:30:39.261 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [/Users/anarkh/anarkh/www/tech-anarkh-spring-demos/011-spring-framework-demo-springmvc/target/011-spring-framework-demo-springmvc-1.0-SNAPSHOT/WEB-INF/classes/tech/anarkh/springframework/springmvc/dao/UserDaoImpl.class]
21:30:39.274 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [/Users/anarkh/anarkh/www/tech-anarkh-spring-demos/011-spring-framework-demo-springmvc/target/011-spring-framework-demo-springmvc-1.0-SNAPSHOT/WEB-INF/classes/tech/anarkh/springframework/springmvc/service/UserServiceImpl.class]
21:30:39.546 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loaded 29 bean definitions from class path resource [springmvc.xml]
21:30:39.711 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
21:30:39.973 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
21:30:39.984 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
21:30:39.995 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
21:30:40.003 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
21:30:40.042 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.ui.context.support.UiApplicationContextUtils - Unable to locate ThemeSource with name 'themeSource': using default [org.springframework.ui.context.support.ResourceBundleThemeSource@791af912]
21:30:40.052 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userController'
21:30:40.136 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userServiceImpl'
21:30:40.140 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userDaoImpl'
21:30:40.147 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler#0'
21:30:40.153 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.handler.SimpleUrlHandlerMapping#0'
21:30:40.350 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.handler.MappedInterceptor#0'
21:30:40.356 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.format.support.FormattingConversionServiceFactoryBean#0'
21:30:40.741 [RMI TCP Connection(2)-127.0.0.1] DEBUG _org.springframework.web.servlet.HandlerMapping.Mappings - 'org.springframework.web.servlet.handler.SimpleUrlHandlerMapping#0' {/**=org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler@216c0f1f}
21:30:40.742 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'mvcCorsConfigurations'
21:30:40.742 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping'
21:30:40.792 [RMI TCP Connection(2)-127.0.0.1] DEBUG _org.springframework.web.servlet.HandlerMapping.Mappings - 'org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping' {}
21:30:40.792 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter'
21:30:40.793 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter'
21:30:40.794 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'localeResolver'
21:30:40.796 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'themeResolver'
21:30:40.798 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'viewNameTranslator'
21:30:40.799 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'flashMapManager'
21:30:40.805 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'mvcContentNegotiationManager'
21:30:40.887 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping'
21:30:41.150 [RMI TCP Connection(2)-127.0.0.1] DEBUG _org.springframework.web.servlet.HandlerMapping.Mappings -
t.p.s.s.c.UserController:
{ [/user]}: list(HttpServletRequest,HttpServletResponse)
21:30:41.202 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - 1 mappings in 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping'
21:30:41.202 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter'
21:30:41.626 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter - ControllerAdvice beans: none
21:30:41.738 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'mvcUriComponentsContributor'
21:30:41.786 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter - ControllerAdvice beans: none
21:30:41.806 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver#0'
21:30:41.919 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver - ControllerAdvice beans: none
21:30:41.920 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver#0'
21:30:41.949 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver#0'
21:30:41.967 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'jspViewResolver'
21:30:44.214 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected AcceptHeaderLocaleResolver
21:30:44.214 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected FixedThemeResolver
21:31:02.141 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator@d57bc91
21:31:03.483 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected org.springframework.web.servlet.support.SessionFlashMapManager@2b4e795e
21:44:08.180 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiTemplate - Looking up JNDI object with name [java:comp/env/spring.liveBeansView.mbeanDomain]
21:44:08.185 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiLocatorDelegate - Converted JNDI name [java:comp/env/spring.liveBeansView.mbeanDomain] not found - trying original name [spring.liveBeansView.mbeanDomain]. javax.naming.NameNotFoundException: 名称[spring.liveBeansView.mbeanDomain]未在此上下文中绑定。找不到[spring.liveBeansView.mbeanDomain]。
21:44:08.185 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiTemplate - Looking up JNDI object with name [spring.liveBeansView.mbeanDomain]
21:44:08.185 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiPropertySource - JNDI lookup for name [spring.liveBeansView.mbeanDomain] threw NamingException with message: 名称[spring.liveBeansView.mbeanDomain]未在此上下文中绑定。找不到[spring.liveBeansView.mbeanDomain]。. Returning null.
21:44:08.195 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - enableLoggingRequestDetails='false': request parameters and headers will be masked to prevent unsafe logging of potentially sensitive data
21:44:08.195 [RMI TCP Connection(2)-127.0.0.1] INFO org.springframework.web.servlet.DispatcherServlet - Completed initialization in 815032 ms