SpringMVC--@RequestMapping註解標註方法解析
SpringMVC--@RequestMapping註解標註方法解析
本文是基於springboot進行原始碼追蹤分析
問題
@RequestMapping註釋的類及方法，Spring是何時，何種方式解析成url與方法的對映關係的？
背景
@RequestMapping註解的解析識別工作是由RequestMappingHandlerMapping類去完成的，會生成對應的RequestMappingInfo例項RequestMappingHandlerMapping類的位置是在org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration通過@Bean註解宣告的org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors方法解析通過@Bean標記的方法，將對應物件轉換為org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.ConfigurationClassBeanDefinition註冊到org.springframework.beans.factory.support.DefaultListableBeanFactoryorg.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons方法中例項化物件，並在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeInitMethods方法中呼叫org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#afterPropertiesSet方法實現@RequestMapping註解類及方法的解析與註冊
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration中定義了WEB MVC相關的自動配置類，就比如org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping、org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter等等的例項化，
解析
類繼承圖
過程
在初始化RequestMappingHandlerMapping物件的時候，因為實現了org.springframework.beans.factory.InitializingBean#afterPropertiesSet方法，所以會呼叫org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeInitMethods方法時，會呼叫RequestMappingHandlerMapping#afterPropertiesSet方法。
// RequestMappingHandlerMapping類中相關程式碼
public void afterPropertiesSet() {
this.config = new RequestMappingInfo.BuilderConfiguration();
this.config.setTrailingSlashMatch(useTrailingSlashMatch());
this.config.setContentNegotiationManager(getContentNegotiationManager());
if (getPatternParser() != null) {
this.config.setPatternParser(getPatternParser());
Assert.isTrue(!this.useSuffixPatternMatch && !this.useRegisteredSuffixPatternMatch,
"Suffix pattern matching not supported with PathPatternParser.");
}
else {
this.config.setSuffixPatternMatch(useSuffixPatternMatch());
this.config.setRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch());
this.config.setPathMatcher(getPathMatcher());
}
// 呼叫父類的方法進行具體的解析
super.afterPropertiesSet();
}
在自身類的重寫方法中進行了一系列的配置，同時呼叫了父類(org.springframework.web.servlet.handler.AbstractHandlerMethodMapping)的afterPropertiesSet方法，而具體的解析方法就在父類中。
// AbstractHandlerMethodMapping中相關程式碼
public void afterPropertiesSet() {
initHandlerMethods();
}
/**
* Scan beans in the ApplicationContext, detect and register handler methods.
* @see #getCandidateBeanNames()
* @see #processCandidateBean
* @see #handlerMethodsInitialized
*/
protected void initHandlerMethods() {
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
//處理每個可能的bean
processCandidateBean(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
protected void processCandidateBean(String beanName) {
Class<?> beanType = null;
try {
beanType = obtainApplicationContext().getType(beanName);
}
catch (Throwable ex) {
// An unresolvable bean type, probably from a lazy bean - let's ignore it.
if (logger.isTraceEnabled()) {
logger.trace("Could not resolve type for bean '" + beanName + "'", ex);
}
}
// beanType上是否由@Controller或者@RequestMapping，如果有則說明是一個待解析的RequestMappingInfo
if (beanType != null && isHandler(beanType)) {
detectHandlerMethods(beanName);
}
}
protected void detectHandlerMethods(Object handler) {
Class<?> handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
Class<?> userType = ClassUtils.getUserClass(handlerType);
//獲取該handler內所有的Method與RquestMappingInfo對映關係
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
(MethodIntrospector.MetadataLookup<T>) method -> {
try {
return getMappingForMethod(method, userType);
}
catch (Throwable ex) {
throw new IllegalStateException("Invalid mapping on handler class [" +
userType.getName() + "]: " + method, ex);
}
});
if (logger.isTraceEnabled()) {
logger.trace(formatMappings(userType, methods));
}
else if (mappingsLogger.isDebugEnabled()) {
mappingsLogger.debug(formatMappings(userType, methods));
}
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
//按method將RequestMappingInfo進行註冊
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
在AbstractHandlerMethodMapping#detectHandlerMethods方法中，獲取當前bean的所有method與RequestMapping對映關係，並進行註冊。
現在繼續看AbstractHandlerMethodMapping#getMappingForMethod，根據方法名即可猜測，這裡就是通過method獲取RequestMappingInfo，具體的實現方法在RequestMappingHandlerMapping#createRequestMappingInfo
// org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#getMappingForMethod實現程式碼
/**
* Uses method and type-level @{@link RequestMapping} annotations to create
* the RequestMappingInfo.
* @return the created RequestMappingInfo, or {@code null} if the method
* does not have a {@code @RequestMapping} annotation.
* @see #getCustomMethodCondition(Method)
* @see #getCustomTypeCondition(Class)
*/
@Override
@Nullable
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
// 根據method建立對應的RquestMappingInfo
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
// 如果方法所在類上也標註了@RequestMapping，則建立類對應的RequestMappingInfo
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
// 將類與方法的requestMappingInfo進行合併，可以理解為獲取完整的url路徑
info = typeInfo.combine(info);
}
String prefix = getPathPrefix(handlerType);
if (prefix != null) {
info = RequestMappingInfo.paths(prefix).options(this.config).build().combine(info);
}
}
// 返回完整url的RequestMappingInfo物件
return info;
}
獲取到對應的RequestMappingInfo之後，就需要進行註冊了，下面看註冊邏輯org.springframework.web.servlet.handler.AbstractHandlerMethodMapping#registerHandlerMethod
public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
// 根據方法生成對應的HandlerMethod，包含了method對應的bean例項，對應的method
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
// 校驗url路徑是否有重複，如果重複會丟擲異常
validateMethodMapping(handlerMethod, mapping);
Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);
for (String path : directPaths) {
this.pathLookup.add(path, mapping);
}
String name = null;
if (getNamingStrategy() != null) {
name = getNamingStrategy().getName(handlerMethod, mapping);
addMappingName(name, handlerMethod);
}
CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
if (corsConfig != null) {
corsConfig.validateAllowCredentials();
this.corsLookup.put(handlerMethod, corsConfig);
}
//MappingRegistration包含RequestMappingInfo、HandlerMethod等
//Map<T, MappingRegistration<T>> registry = new HashMap<>();
this.registry.put(mapping,
new MappingRegistration<>(mapping, handlerMethod, directPaths, name, corsConfig != null));
}
finally {
this.readWriteLock.writeLock().unlock();
}
}
總結
-
契機：給需要暴漏介面的方法、類上新增
@RequestMapping註解 -
時機：由於
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping間接實現了org.springframework.beans.factory.InitializingBean#afterPropertiesSet方法，所以在RequestMappingHandlerMapping物件初始化的時候，會呼叫自身的org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#afterPropertiesSet方法，自身進行一系列配置之後，就會呼叫父類org.springframework.web.servlet.handler.AbstractHandlerMethodMapping#afterPropertiesSet的方法進行@RequestMapping標註方法的解析 -
解析：主體流程都是在
AbstractHandlerMethodMapping類中的方法，具體的實現通過抽象方法的形式讓子類RequestMappingHandlerMapping進行實現。具體根據method生成對應的RequestMappingInfo是在RequestMappingHandlerMapping類中的方法org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#getMappingForMethod。過程中會先解析標註了@RequestMapping的方法，生成方法對應的RequestMappingInfo例項；如果方法所在的類上也有@RequestMapping標註的註解，生成類對應的RequestMappingInfo例項，然後將兩者進行合併，也就是生成完整的url對映物件 -
註冊：在解析完所有的方法之後，將
RequestMappingInfo進行註冊，註冊容器位於AbstractHandlerMethodMapping類中，容器為MappingRegistry mappingRegistry = new MappingRegistry()，而MappingRegistry中實際儲存的容器為Map<T, MappingRegistration<T>> registry = new HashMap<>()。其中key為對應的RequestMappingInfo，value為MappingRegistration，其中MappingRegistration包含了RequestMappingInfo、HandlerMethod