SpringMVC--@RequestMapping注解标注方法解析

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SpringMVC--@RequestMapping注解标注方法解析

本文是基于springboot进行源码追踪分析

问题

• @RequestMapping注释的类及方法，Spring是何时，何种方式解析成url与方法的映射关系的？

背景

• @RequestMapping注解的解析识别工作是由RequestMappingHandlerMapping类去完成的，会生成对应的RequestMappingInfo实例
• RequestMappingHandlerMapping类的位置是在org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration通过@Bean注解声明的
• org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors方法解析通过@Bean标记的方法，将对应对象转换为org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.ConfigurationClassBeanDefinition注册到org.springframework.beans.factory.support.DefaultListableBeanFactory
• org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons方法中实例化对象，并在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeInitMethods方法中调用org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#afterPropertiesSet方法实现@RequestMapping注解类及方法的解析与注册

org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration中定义了WEB MVC相关的自动配置类，就比如org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping、org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter等等的实例化，

解析

类继承图

过程

在初始化RequestMappingHandlerMapping对象的时候，因为实现了org.springframework.beans.factory.InitializingBean#afterPropertiesSet方法，所以会调用org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeInitMethods方法时，会调用RequestMappingHandlerMapping#afterPropertiesSet方法。

// RequestMappingHandlerMapping类中相关代码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());
}
// 调用父类的方法进行具体的解析
super.afterPropertiesSet();
}


在自身类的重写方法中进行了一系列的配置，同时调用了父类(org.springframework.web.servlet.handler.AbstractHandlerMethodMapping)的afterPropertiesSet方法，而具体的解析方法就在父类中。

// AbstractHandlerMethodMapping中相关代码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)) {
//处理每个可能的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，如果有则说明是一个待解析的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);
//获取该handler内所有的Method与RquestMappingInfo映射关系
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将RequestMappingInfo进行注册
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}


在AbstractHandlerMethodMapping#detectHandlerMethods方法中，获取当前bean的所有method与RequestMapping映射关系，并进行注册。

现在继续看AbstractHandlerMethodMapping#getMappingForMethod，根据方法名即可猜测，这里就是通过method获取RequestMappingInfo，具体的实现方法在RequestMappingHandlerMapping#createRequestMappingInfo

// org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#getMappingForMethod实现代码/**
* 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) {
// 根据method创建对应的RquestMappingInfo
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
// 如果方法所在类上也标注了@RequestMapping，则创建类对应的RequestMappingInfo
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
// 将类与方法的requestMappingInfo进行合并，可以理解为获取完整的url路径
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对象
return info;
}


获取到对应的RequestMappingInfo之后，就需要进行注册了，下面看注册逻辑org.springframework.web.servlet.handler.AbstractHandlerMethodMapping#registerHandlerMethod

public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
// 根据方法生成对应的HandlerMethod，包含了method对应的bean实例，对应的method
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
// 校验url路径是否有重复，如果重复会抛出异常
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();
}
}


总结

• 契机：给需要暴漏接口的方法、类上添加@RequestMapping注解

• 时机：由于org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping间接实现了org.springframework.beans.factory.InitializingBean#afterPropertiesSet方法，所以在RequestMappingHandlerMapping对象初始化的时候，会调用自身的org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#afterPropertiesSet方法，自身进行一系列配置之后，就会调用父类org.springframework.web.servlet.handler.AbstractHandlerMethodMapping#afterPropertiesSet的方法进行@RequestMapping标注方法的解析

• 解析：主体流程都是在AbstractHandlerMethodMapping类中的方法，具体的实现通过抽象方法的形式让子类RequestMappingHandlerMapping进行实现。具体根据method生成对应的RequestMappingInfo是在RequestMappingHandlerMapping类中的方法org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#getMappingForMethod。过程中会先解析标注了@RequestMapping的方法，生成方法对应的RequestMappingInfo实例；如果方法所在的类上也有@RequestMapping标注的注解，生成类对应的RequestMappingInfo实例，然后将两者进行合并，也就是生成完整的url映射对象

• 注册：在解析完所有的方法之后，将RequestMappingInfo进行注册，注册容器位于AbstractHandlerMethodMapping类中，容器为 MappingRegistry mappingRegistry = new MappingRegistry()，而MappingRegistry 中实际存储的容器为Map<T, MappingRegistration<T>> registry = new HashMap<>()。其中key为对应的RequestMappingInfo，value为MappingRegistration，其中MappingRegistration包含了RequestMappingInfo、HandlerMethod