剖析Spring MVC,介绍Spring MVC中的HandlerMapping。
在前面文章中，DispatcherServlet接收到请求后通过HandlerMapping,HandlerAdapter来处理请求，这一章先来看HandlerMapping是如何工作的。
graph BT
AbstractHandlerMapping -.-> HandlerMapping
AbstractHandlerMethodMapping --> AbstractHandlerMapping
RequestMappingInfoHandlerMapping --> AbstractHandlerMethodMapping
RequestMappingHandlerMapping --> RequestMappingInfoHandlerMapping
AbstractUrlHandlerMapping --> AbstractHandlerMapping
AbstractDetectingUrlHandlerMapping --> AbstractUrlHandlerMapping
BeanNameUrlHandlerMapping --> AbstractDetectingUrlHandlerMapping
SimpleUrlHandlerMapping --> AbstractUrlHandlerMapping1. HandlerMapping
首先看HandlerMappings的初始化，在DispatcherServlet中initStrategies方法初始化了HandlerMappings。来看初始化的方法：
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
//默认为true
if (this.detectAllHandlerMappings) {
// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
// 从容器获取所有的HandlerMappings
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.
// 排序
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
//指定mapping
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.
// 没有获取到则穿件默认到handlerMappings
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
}
}
}2. AbstractHandlerMapping
再来看HandlerMapping是如何创建的，AbstractHandlerMapping实现了HandlerMapping,并继承了WebApplicationObjectSupport。在应用初始化时会调用WebApplicationObjectSupport抽象方法initApplicationContext,来看在AbstractHandlerMapping中的initApplicationContext方法：
/**
* Initializes the interceptors.
* @see #extendInterceptors(java.util.List)
* @see #initInterceptors()
*/
@Override
protected void initApplicationContext() throws BeansException {
// 并没有实现
extendInterceptors(this.interceptors);
// 把所有MappedInterceptor类型的bean添加到mappedInterceptors也就是adaptedInterceptors中
detectMappedInterceptors(this.adaptedInterceptors);
// 这里有版本变化
// 初始化interceptors,将interceptor转换成HandlerInterceptor或者WebRequestHandlerInterceptorAdapter到adaptedInterceptors中
//this.adaptedInterceptors.add(adaptInterceptor(interceptor))
//
//if (interceptor instanceof HandlerInterceptor) {
// return (HandlerInterceptor) interceptor;
//}
//else if (interceptor instanceof WebRequestInterceptor) {
// return new WebRequestHandlerInterceptorAdapter((WebRequestInterceptor) interceptor);
//}
initInterceptors();
}HandlerMapping是通过getHandler方法来获取Handler和Interceptor的，来看AbstractHandlerMapping中具体实现：
// final不可重写
@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 通过getHandlerInternal方法获取getHandlerInternal，getHandlerInternal是一个抽象模板方法
Object handler = getHandlerInternal(request);
if (handler == null) {
// 获取默认的handler，获取的handler为本类的一个属性，通过set方法设置的
handler = getDefaultHandler();
}
//都没有获取到handler则返回空，在DispacthServlet中会返回404
if (handler == null) {
return null;
}
// Bean name or resolved handler?
// 如果handler类型为String则通过名字获取bean
if (handler instanceof String) {
String handlerName = (String) handler;
//protected final ApplicationContext obtainApplicationContext() {
// ApplicationContext applicationContext = getApplicationContext();
// Assert.state(applicationContext != null, "No ApplicationContext");
// return applicationContext;
//}
handler = obtainApplicationContext().getBean(handlerName);
}
// 通过handler，request创建HandlerExecutionChain对象
//protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
// //通过handler创建HandlerExecutionChain
// HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
// (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
//
// String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
// for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
// if (interceptor instanceof MappedInterceptor) {
// MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
// if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
// //通过url设置MappedInterceptor
// chain.addInterceptor(mappedInterceptor.getInterceptor());
// }
// }
// else {
// //添加非MappedInterceptor的HandlerInterceptor
// chain.addInterceptor(interceptor);
// }
// }
// return chain;
//}
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
// 查看request里是否有跨域信息
if (CorsUtils.isCorsRequest(request)) {
// 获取配置信息
CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
//protected HandlerExecutionChain getCorsHandlerExecutionChain(HttpServletRequest request,
// HandlerExecutionChain chain, @Nullable CorsConfiguration config) {
// //如果请求为options
// if (CorsUtils.isPreFlightRequest(request)) {
// HandlerInterceptor[] interceptors = chain.getInterceptors();
// //使用PreFlightHandler
// chain = new HandlerExecutionChain(new PreFlightHandler(config), interceptors);
// }
// else {
// //非ptions添加CorsInterceptor
// chain.addInterceptor(new CorsInterceptor(config));
// }
// return chain;
//}
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}从上面的分析中看到获取handler的方法是getHandlerInternal,这是一个抽象模板方法，来看他的实现，在AbstractUrlHandlerMapping和AbstractHandlerMethodMapping中实现了getHandlerInternal。
3. AbstractUrlHandlerMapping
先看AbstractUrlHandlerMapping中的getHandlerInternal
/**
* Look up a handler for the URL path of the given request.
* @param request current HTTP request
* @return the handler instance, or {@code null} if none found
*/
@Override
@Nullable
protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
// 通过request获取查找路径
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
// 通过路径和request获取handler
Object handler = lookupHandler(lookupPath, request);
// 如果未获取到handler
if (handler == null) {
// We need to care for the default handler directly, since we need to
// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
Object rawHandler = null;
// rootHandler
if ("/".equals(lookupPath)) {
rawHandler = getRootHandler();
}
// 默认handler
if (rawHandler == null) {
rawHandler = getDefaultHandler();
}
// 如果String类型获取bean
if (rawHandler != null) {
// Bean name or resolved handler?
if (rawHandler instanceof String) {
String handlerName = (String) rawHandler;
rawHandler = obtainApplicationContext().getBean(handlerName);
}
// 抽象方法，校验
validateHandler(rawHandler, request);
// 设置PathExposingHandlerInterceptor，UriTemplateVariablesHandlerInterceptor
handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
}
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Mapping [" + lookupPath + "] to " + handler);
}
else if (handler == null && logger.isTraceEnabled()) {
logger.trace("No handler mapping found for [" + lookupPath + "]");
}
return handler;
}主要调用了三个方法：lookupHandler,validateHandler,buildPathExposingHandler,来看他们的代码
lookupHandler:通过url和request获取handlerrotected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception { // Direct match? // 从handlerMap获取handler，从上文中我们没有发现handlerMap是从哪里赋值 // 通过搜索发现handlerMap的put方法在registerHandler中调用 // registerHandler被SimpleUrlHandlerMapping中initApplicationContext调用 // registerHandler被AbstractDetectingUrlHandlerMapping中detectHandlers调用,detectHandlers又被initApplicationContext调用 // detectHandlers调用模板方法determineUrlsForHandler，该方法在子类BeanNameUrlHandlerMapping中实现 // 这些方法重写WebApplicationObjectSupport // 也就是说this.handlerMap在应用初始化的时候就会赋值 Object handler = this.handlerMap.get(urlPath); if (handler != null) { // Bean name or resolved handler? // 如果String从容器中获取handler if (handler instanceof String) { String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } //校验，设置Interceptor validateHandler(handler, request); return buildPathExposingHandler(handler, urlPath, urlPath, null); } // Pattern match? Pattern匹配 List<String> matchingPatterns = new ArrayList<>(); for (String registeredPattern : this.handlerMap.keySet()) { if (getPathMatcher().match(registeredPattern, urlPath)) { matchingPatterns.add(registeredPattern); } else if (useTrailingSlashMatch()) { if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) { matchingPatterns.add(registeredPattern +"/"); } } } String bestMatch = null; Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath); if (!matchingPatterns.isEmpty()) { matchingPatterns.sort(patternComparator); if (logger.isDebugEnabled()) { logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns); } bestMatch = matchingPatterns.get(0); } if (bestMatch != null) { handler = this.handlerMap.get(bestMatch); if (handler == null) { if (bestMatch.endsWith("/")) { handler = this.handlerMap.get(bestMatch.substring(0, bestMatch.length() - 1)); } if (handler == null) { throw new IllegalStateException( "Could not find handler for best pattern match [" + bestMatch + "]"); } } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } validateHandler(handler, request); String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath); // There might be multiple 'best patterns', let's make sure we have the correct URI template variables // for all of them Map<String, String> uriTemplateVariables = new LinkedHashMap<>(); for (String matchingPattern : matchingPatterns) { if (patternComparator.compare(bestMatch, matchingPattern) == 0) { Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath); Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars); uriTemplateVariables.putAll(decodedVars); } } if (logger.isDebugEnabled()) { logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables); } return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables); } // No handler found... // 没有找到handler返回空 return null; }validateHandler：空的方法buildPathExposingHandler：添加PathExposingHandlerInterceptor,UriTemplateVariablesHandlerInterceptor拦截器，主要作用是request添加一些属性，例如request.setAttribute(URI_TEMPLATE_VARIABLES_ATTRIBUTE, uriTemplateVariables)。
子类SimpleUrlHandlerMapping,AbstractDetectingUrlHandlerMapping,BeanNameUrlHandlerMapping在上面代码注释中介绍。
4. AbstractHandlerMethodMapping
首先看到AbstractHandlerMethodMapping实现了InitializingBean并重写了afterPropertiesSet（初始化bean的时候会执行该方法）,可以看到调用initHandlerMethods,来看这个方法：
protected void initHandlerMethods() {
if (logger.isDebugEnabled()) {
logger.debug("Looking for request mappings in application context: " + getApplicationContext());
}
String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
obtainApplicationContext().getBeanNamesForType(Object.class));
for (String beanName : beanNames) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
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.isDebugEnabled()) {
logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
}
}
// 检查是否含有Controller或者RequestMapping注释
// (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
// AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class))
if (beanType != null && isHandler(beanType)) {
detectHandlerMethods(beanName);
}
}
}
//handlerMethodsInitialized是空的
handlerMethodsInitialized(getHandlerMethods());
}可以看到关键调用了detectHandlerMethods方法，来看detectHandlerMethods:
// Look for handler methods in a handler.
protected void detectHandlerMethods(final Object handler) {
//获取handler类型
Class<?> handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
//获取真实类型
//if (clazz.getName().contains(CGLIB_CLASS_SEPARATOR)) {
// Class<?> superclass = clazz.getSuperclass();
// if (superclass != null && Object.class != superclass) {
// return superclass;
// }
// }
//return clazz;
final Class<?> userType = ClassUtils.getUserClass(handlerType);
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.isDebugEnabled()) {
logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
}
//遍历注册HandlerMethod
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}来看上面的方法selectMethods,getMappingForMethod,registerHandlerMethod，具体看这三个方法
selectMethods
可以看到回调了public static <T> Map<Method, T> selectMethods(Class<?> targetType, final MetadataLookup<T> metadataLookup) { final Map<Method, T> methodMap = new LinkedHashMap<>(); Set<Class<?>> handlerTypes = new LinkedHashSet<>(); Class<?> specificHandlerType = null; //把自身添加到handlerTypes if (!Proxy.isProxyClass(targetType)) { specificHandlerType = ClassUtils.getUserClass(targetType); handlerTypes.add(specificHandlerType); } handlerTypes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetType)); for (Class<?> currentHandlerType : handlerTypes) { final Class<?> targetClass = (specificHandlerType != null ? specificHandlerType : currentHandlerType); ReflectionUtils.doWithMethods(currentHandlerType, method -> { Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass); //回调inspect（）方法给个函数生成RequestMappingInfo T result = metadataLookup.inspect(specificMethod); if (result != null) { Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod); if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) { //将生成的RequestMappingInfo保存到methodMap中 methodMap.put(specificMethod, result); } } }, ReflectionUtils.USER_DECLARED_METHODS); } //返回保存函数映射信息后的methodMap return methodMap; }getMappingForMethod,来看getMappingForMethod是如何生成RequestMappingInfo。getMappingForMethod是一个模板方法在子类RequestMappingHandlerMapping实现。getMappingForMethodprotected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) { //构建RequestMappingInfo RequestMappingInfo info = createRequestMappingInfo(method); if (info != null) { RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType); if (typeInfo != null) { info = typeInfo.combine(info); } } return info; } private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) { RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class); RequestCondition<?> condition = (element instanceof Class ? getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element)); return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null); } protected RequestMappingInfo createRequestMappingInfo( RequestMapping requestMapping, @Nullable RequestCondition<?> customCondition) { //构建了RequestMappingInfo返回 RequestMappingInfo.Builder builder = RequestMappingInfo .paths(resolveEmbeddedValuesInPatterns(requestMapping.path())) .methods(requestMapping.method()) .params(requestMapping.params()) .headers(requestMapping.headers()) .consumes(requestMapping.consumes()) .produces(requestMapping.produces()) .mappingName(requestMapping.name()); if (customCondition != null) { builder.customCondition(customCondition); } return builder.options(this.config).build(); }registerHandlerMethod:把HandlerMethod放到map中
再来看如何获取
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
//获取url
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
if (logger.isDebugEnabled()) {
logger.debug("Looking up handler method for path " + lookupPath);
}
//锁
this.mappingRegistry.acquireReadLock();
try {
//获取构建HandlerMethod
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
if (logger.isDebugEnabled()) {
if (handlerMethod != null) {
logger.debug("Returning handler method [" + handlerMethod + "]");
}
else {
logger.debug("Did not find handler method for [" + lookupPath + "]");
}
}
//调用createWithResolvedBean返回
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
this.mappingRegistry.releaseReadLock();
}
}来看lookupHandlerMethod
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings...
addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
}
if (!matches.isEmpty()) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
matches.sort(comparator);
if (logger.isTraceEnabled()) {
logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches);
}
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
if (CorsUtils.isPreFlightRequest(request)) {
return PREFLIGHT_AMBIGUOUS_MATCH;
}
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0) {
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" +
request.getRequestURL() + "': {" + m1 + ", " + m2 + "}");
}
}
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.handlerMethod;
}
else {
return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
}
}总结：
在DispatcherServlet的doDispatch获取到了HandlerExecutionChain。
HandlerExecutionChain包含Handler,HandlerInterceptor:
HandlerInterceptor：在AbstractHandlerMapping中获取。Handler：由AbstractHandlerMapping的子类实现getHandlerInternal获取。
AbstractHandlerMapping有俩条分支：
AbstractUrlHandlerMapping：简单的说Handler就是Controller类，片面理解为一个Controller只能对应一个请求，可以实现AbstractController及子类。在实际中也就是BeanNameUrlHandlerMapping，SimpleUrlHandlerMapping的使用。AbstractHandlerMethodMapping：使用最多的HandlerMethod，也就是映射到方法。HandlerMethod类型的Handler。RequestMappingHandlerMapping的使用。