在之前的文章说过，springmvc在要初始化spring容器时，会提前注册一个监听器，当spring容器完成刷新后，此监听器的回调方法会收到回调通知，会执行如下方法
public void onApplicationEvent(ContextRefreshedEvent event) {
FrameworkServlet.this.onApplicationEvent(event);
}
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
这个方法就是给DispatcherServlet的几个重要属性赋值，因为这个servlet是整个springmvc所有请求的入口，所以需要对其属性赋值，而这些属性值又是通过从spring容器中获取的。
本文就以HandlerMapping为例，来看下springmvc对其的赋值方式。HandlerMapping在springmvc中主要作用是根据http的请求，找到对应controller的某个执行方法
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
// We keep HandlerMappings in sorted order.
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerMapping later.
}
}
// Ensure we have at least one HandlerMapping, by registering
// a default HandlerMapping if no other mappings are found.
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
for (HandlerMapping mapping : this.handlerMappings) {
if (mapping.usesPathPatterns()) {
this.parseRequestPath = true;
break;
}
}
}
上面的这个方法，springmvc会先从容器找是否有handlerMapping，若有，直接从容器的找出来并赋值。若没有，则走自己的默认策略。
因此，先来看下如何在spring容器刷新时便加入HandlerMapping实例，springmvc提供了WebMvcConfigurationSupport这个类，里面定义了几个重要组件的bean方法，但是类本身不是component，因此程序可以手动继承这个类，并标注为Component，spring容器在初始化时，便会去生成这些bean实例，或者是通过springmvc提供的一个简便的注解@EnableWebMvc，本质上也是通过继承WebMvcConfigurationSupport这个类来实现的
public class WebMvcConfigurationSupport {
@Bean
@SuppressWarnings("deprecation")
public RequestMappingHandlerMapping requestMappingHandlerMapping(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
//省略
return mapping;
}
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcValidator") Validator validator) {
//省略
return adapter;
}
}
若是应用程序中，没有手动继承WebMvcConfigurationSupport及没用注解@EnableWebMvc，那么spring容器中便不会存在RequestMappingHandlerMapping 等几个重要组件，此时，springmvc是有补救方式的，如下
protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
if (defaultStrategies == null) {
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
}
String key = strategyInterface.getName();
String value = defaultStrategies.getProperty(key);
if (value != null) {
String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
List<T> strategies = new ArrayList<>(classNames.length);
for (String className : classNames) {
try {
Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
Object strategy = createDefaultStrategy(context, clazz);
strategies.add((T) strategy);
}
}
return strategies;
}
else {
return Collections.emptyList();
}
}
springmvc默认组件的配置是在DispatcherServlet同级路径下的一个DispatcherServlet.properties文件，这文件里面定了springmvc几个组件默认的实现类
org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
org.springframework.web.servlet.function.support.RouterFunctionMapping
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
org.springframework.web.servlet.function.support.HandlerFunctionAdapter
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver
org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager
springmvc会先将DispatcherServlet.properties文件内容都读取到DispatcherServlet的defaultStrategies成员变量中，然后再获取到对应组件的实现类列表，再通过spring容器去创建这些对象。
protected Object createDefaultStrategy(ApplicationContext context, Class<?> clazz) {
return context.getAutowireCapableBeanFactory().createBean(clazz);
}
当initStrategies这个方法执行完毕时，springmvc的几大重要组件便初始化完毕了，然后程序回到initWebApplicationContext方法，将spring容器添加到servletContext的属性之中。
初始化完组件后，springmvc容器便启动成功了，可以对外提供web服务
