从本文开始，来分析下springmvc几个重要组件是如何工作的。
首选，来看下HandlerMapping
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
这个接口主要有这个方法，通过request获取一个HandlerExecutionChain对象，这个对象就是包含了两个成员变量
//handler就是应用程序中定义的controller
private final Object handler;
//拦截器，在controller方法的执行前后加入自己的逻辑，类似于切面
private final List<HandlerInterceptor> interceptorList = new ArrayList<>();
简单的说，HandlerMapping就是通过http请求查询到对应controller和interceptor。
springmvc默认提供的实现类有三个，分别为RequestMappingHandlerMapping、BeanNameUrlHandlerMapping、RouterFunctionMapping。
日常开发中用的最多的便是RequestMappingHandlerMapping，因此本文主要来看下这个这个bean对象的初始化流程
初始化流程便是定义在WebMvcConfigurationSupport类中
@Bean
@SuppressWarnings("deprecation")
public RequestMappingHandlerMapping requestMappingHandlerMapping(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();
mapping.setOrder(0);
mapping.setInterceptors(getInterceptors(conversionService, resourceUrlProvider));
mapping.setContentNegotiationManager(contentNegotiationManager);
mapping.setCorsConfigurations(getCorsConfigurations());
PathMatchConfigurer pathConfig = getPathMatchConfigurer();
if (pathConfig.getPatternParser() != null) {
mapping.setPatternParser(pathConfig.getPatternParser());
}
else {
mapping.setUrlPathHelper(pathConfig.getUrlPathHelperOrDefault());
mapping.setPathMatcher(pathConfig.getPathMatcherOrDefault());
Boolean useSuffixPatternMatch = pathConfig.isUseSuffixPatternMatch();
if (useSuffixPatternMatch != null) {
mapping.setUseSuffixPatternMatch(useSuffixPatternMatch);
}
Boolean useRegisteredSuffixPatternMatch = pathConfig.isUseRegisteredSuffixPatternMatch();
if (useRegisteredSuffixPatternMatch != null) {
mapping.setUseRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch);
}
}
Boolean useTrailingSlashMatch = pathConfig.isUseTrailingSlashMatch();
if (useTrailingSlashMatch != null) {
mapping.setUseTrailingSlashMatch(useTrailingSlashMatch);
}
if (pathConfig.getPathPrefixes() != null) {
mapping.setPathPrefixes(pathConfig.getPathPrefixes());
}
return mapping;
}
首先就是设置order，值越小，越先执行。程序中可能存在多个HandlerMapping实现类，因此执行的先后顺序是可以指定的。
然后就是可以添加拦截器interceptor
protected final Object[] getInterceptors(
FormattingConversionService mvcConversionService,
ResourceUrlProvider mvcResourceUrlProvider) {
if (this.interceptors == null) {
InterceptorRegistry registry = new InterceptorRegistry();
addInterceptors(registry);
registry.addInterceptor(new ConversionServiceExposingInterceptor(mvcConversionService));
registry.addInterceptor(new ResourceUrlProviderExposingInterceptor(mvcResourceUrlProvider));
this.interceptors = registry.getInterceptors();
}
return this.interceptors.toArray();
}
springmvc默认会添加两个拦截器ConversionServiceExposingInterceptor和ResourceUrlProviderExposingInterceptor，这里有一个很重要的方法addInterceptors，这方法就是给子类继承重写，让应用程序可以手动添加interceptor
每个拦截器是一个InterceptorRegistration对象，包含了三个成员变量
//拦截器对象
private final HandlerInterceptor interceptor;
//符合拦截器执行的路径模式
private final List<String> includePatterns = new ArrayList<>();
//符合拦截器执行的路径模式
private final List<String> excludePatterns = new ArrayList<>();
//路径匹配器
@Nullable
private PathMatcher pathMatcher;
//拦截器的执行顺序
private int order = 0;
HandlerMapping除了添加拦截器外，还有一个比较重要的方法，是添加跨域信息相关的，同样有个方法addCorsMappings可以让子类重写，由应用程序添加跨域相关的配置。
HandlerMapping其他属性由于应用程序一般不需要去修改，因此这里不再讲述了，当生成RequestMappingHandlerMapping对象后，由于这个类还实现了InitializingBean接口，因此还会执行初始化方法afterPropertiesSet
public void afterPropertiesSet() {
this.config = new RequestMappingInfo.BuilderConfiguration();
this.config.setUrlPathHelper(getUrlPathHelper());
this.config.setPathMatcher(getPathMatcher());
this.config.setSuffixPatternMatch(useSuffixPatternMatch());
this.config.setTrailingSlashMatch(useTrailingSlashMatch());
this.config.setRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch());
this.config.setContentNegotiationManager(getContentNegotiationManager());
super.afterPropertiesSet();
}
可以看到这个方法主要是将HandlerMapping的相关属性值赋值给内部成员RequestMappingInfo.BuilderConfiguration的属性，然后再调用initHandlerMethods方法
protected void initHandlerMethods() {
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
processCandidateBean(beanName);
}
}
}
这个方法中，循环处理容器的beanName列表，然后取出beanName对应的Class对象，判断该class对象是否为Handler，判断标准就是看类是否有注解了Controller或者RequestMapping，若是Handler，则执行detectHandlerMethods
protected void detectHandlerMethods(Object handler) {
Class<?> handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
Class<?> userType = ClassUtils.getUserClass(handlerType);
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
(MethodIntrospector.MetadataLookup<T>) method -> {
try {
//根据Method对象，获取对应的RequestMappingInfo对象
return getMappingForMethod(method, userType);
}
catch (Throwable ex) {
throw new IllegalStateException("Invalid mapping on handler class [" +
userType.getName() + "]: " + method, ex);
}
});
//....中间日志省略
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
这个方法主要分为两个步骤
- MethodIntrospector.selectMethods 获取handler（controller）下Method对象及其对应的RequestMappingInfo对象，其中RequestMappingInfo对象就是对方法注解@RequestMapping相关属性值的封装（也会结合注解在类上面的@RequestMapping）
- 将Method对象，RequestMappingInfo对象维护到HandlerMapping中，当然还有包含url相关的，这样后续请求到来，就可根据url映射出对应的handler。
上述步骤1涉及到的细节很多，这里不展开了，主要来看下步骤2，registerHandlerMethod的处理
public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
validateMethodMapping(handlerMethod, mapping);
this.mappingLookup.put(mapping, handlerMethod);
List<String> directUrls = getDirectUrls(mapping);
for (String url : directUrls) {
this.urlLookup.add(url, mapping);
}
String name = null;
if (getNamingStrategy() != null) {
name = getNamingStrategy().getName(handlerMethod, mapping);
addMappingName(name, handlerMethod);
}
CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
if (corsConfig != null) {
this.corsLookup.put(handlerMethod, corsConfig);
}
this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod, directUrls, name));
}
finally {
this.readWriteLock.writeLock().unlock();
}
}
这方法主要是对HandlerMapping内部一些map的维护
//RequestMappingInfo，MappingRegistration
private final Map<T, MappingRegistration<T>> registry = new HashMap<>();
//RequestMappingInfo， HandlerMethod
private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<>();
//url， RequestMappingInfo列表
private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<>();
//name, HandlerMethod
private final Map<String, List<HandlerMethod>> nameLookup = new ConcurrentHashMap<>();
//cors
private final Map<HandlerMethod, CorsConfiguration> corsLookup = new ConcurrentHashMap<>();
通过这些map，程序可以快速的根据请求url定位到具体的handler，再执行对应的方法。这个请求的流程后续再讲述。
总结，RequestMapping实例化主要是对内部重要的属性进行赋值，方便应用程序可根据http请求的相关信息，比如url，header头等等，找到对应的Controller，并执行相应的方法。
