一、HandlerMapping類圖
默認情況下，SpringMVC 將加載當前系統中所有實現了HandlerMapping 接口的bean。如果只期望SpringMVC加載指定的handlermapping 時，可以修改web.xml中的DispatcherServlet的初始參數，將detectAllHandlerMappings的值設置爲false:
<init-param>
<param-name>detectAllHandlerMappings</param-name>
<param-value> false</param-value>
</ init-param>
此時Spring MVC將查找名爲“ handlerMapping”的bean, 並作爲當前系統中唯一的handlermapping。如果沒有定義handlerMapping 的話，則SpringMVC將按照org. Springframework.web.servlet.,DispatcherServlet所在目錄下的DispatcherServlet.properties中所定義的org.Springframework.web.servlet.HandlerMapping的內容來加載默認的handlerMapping (用戶沒有自定義Strategies的情況下)。
二、初始化HandlerMethod
2.1 初始化HandlerMethod流程
(1) 獲取容器中所有的Bean，篩選出類上有@Controller或@RequestMapping註解的類，作爲候選Handler
(2) 遍歷候選Bean所有方法，如果方法上沒有@RequestMapping註解則忽略該方法，否則獲取方法和類上的@RequestMapping註解併合並，創建RequestMappingInfo實例
(3) 註冊RequestMappingInfo與HandlerMethod映射信息：
將Handler和Method封裝到HandlerMethod中，建立RequestMappingInfo --> HandlerMethod映射關係
建立directUrl --> List<RequestMappingInfo>映射關係，同一個URL處理的請求方法不同：Get、Post等
建立name --> List<RequestMappingInfo>映射關係
建立HandlerMethod --> CorsConfiguration映射關係
建立RequestMappingInfo --> MappingRegistration映射關係，MappingRegistration封裝了RequestMappingInfo、HandlerMethod、directUrls、name
2.2 RequestMappingHandlerMapping
2.2.1 afterPropertiesSet
從類圖中可知RequestMappingHandlerMapping實現InitializingBean接口，下面看afterPropertiesSet方法
public void afterPropertiesSet() {
// 用於請求映射目的配置選項的容器。 創建RequestMappingInfo實例需要這種配置，但是通常在所有RequestMappingInfo實例中使用。
this.config = new RequestMappingInfo.BuilderConfiguration();
this.config.setUrlPathHelper(getUrlPathHelper());
this.config.setPathMatcher(getPathMatcher());
this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
this.config.setContentNegotiationManager(getContentNegotiationManager());
super.afterPropertiesSet();
}
2.2.2 getMappingForMethod
// 獲取方法上的@RequestMapping註解，並創建RequestMappingInfo。調用者傳送門：2.3.5
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
info = typeInfo.combine(info);
}
String prefix = getPathPrefix(handlerType);
if (prefix != null) {
info = RequestMappingInfo.paths(prefix).options(this.config).build().combine(info);
}
}
return info;
}
2.2.3 根據@RequestMapping創建RequestMappingInfo createRequestMappingInfo
根據@RequestMapping註解創建RequestMappingInfo時，有getCustomTypeCondition、getCustomMethodCondition這兩個方法值得我們關注，可以擴展RequestMappingHandlerMapping實現@RequestMapping註解上的自定義RequestCondition。那麼RequestCondition在哪裏會用到呢？傳送門：4.1
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) {
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();
}
2.3 AbstractHandlerMethodMapping
2.3.1 afterPropertiesSet
public void afterPropertiesSet() {
initHandlerMethods();
}
2.3.2 initHandlerMethods
protected void initHandlerMethods() {
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
processCandidateBean(beanName);
}
}
// 輸出總計包括檢測到的映射+通過registerMapping的顯式註冊
handlerMethodsInitialized(getHandlerMethods());
}
2.3.3 獲取候選Bean名稱 getCandidateBeanNames
// 在應用程序上下文中確定候選bean的名稱
protected String[] getCandidateBeanNames() {
return (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
obtainApplicationContext().getBeanNamesForType(Object.class));
}
2.3.4 處理候選Bean processCandidateBean
// 確定指定的候選bean的類型，如果標識爲handler類型，則調用 {@link #detectHandlerMethods}
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);
}
}
// isHandler由子類實現，類上有@Controller或@RequestMapping註解
if (beanType != null && isHandler(beanType)) {
detectHandlerMethods(beanName);
}
}
2.3.5 查找Handler中處理請求方法 detectHandlerMethods
// 在指定的handler bean中查找處理程序方法。{@link #detectHandlerMethods}避免了bean的創建。
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 {
// 子類實現獲取方法或類上的@RequestMapping，封裝爲RequestMappingInfo。方法上有@RequestMapping時纔會獲取類上的@RequestMapping。傳送門：2.2.2
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));
}
methods.forEach((method, mapping) -> {
// 在目標類型上選擇一個可調用的方法：給定方法本身（如果實際在目標類型上公開），或者在目標類型的一個接口或目標類型本身上對應的方法。
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
2.3.6 註冊Handler中處理請求方法 registerHandlerMethod
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
this.mappingRegistry.register(mapping, handler, method);
}
2.4 HandlerMethod註冊容器 MappingRegistry
2.4.1 註冊HandlerMethod register
// RequestMappingInfo --> MappingRegistration<RequestMappingInfo>
private final Map<T, MappingRegistration<T>> registry = new HashMap<>();
// RequestMappingInfo --> HandlerMethod
private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<>();
// url(@RequestMapping註解上配置的) --> RequestMappingInfo
private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<>();
// name(HandlerMethodMappingNamingStrategy生成) --> List<HandlerMethod>
private final Map<String, List<HandlerMethod>> nameLookup = new ConcurrentHashMap<>();
// HandlerMethod --> CorsConfiguration
private final Map<HandlerMethod, CorsConfiguration> corsLookup = new ConcurrentHashMap<>();
public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
// 創建HandlerMethod實例，封裝了handler、method
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
assertUniqueMethodMapping(handlerMethod, mapping);
this.mappingLookup.put(mapping, handlerMethod);
// 獲取@RequestMapping註解上配置的非正則表達式路徑
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);
}
// 方法或類上的@CrossOrigin註解，封裝成CorsConfiguration，由子類實現
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();
}
}
2.4.2 校驗映射關係是否唯一 assertUniqueMethodMapping
private void assertUniqueMethodMapping(HandlerMethod newHandlerMethod, T mapping) {
HandlerMethod handlerMethod = this.mappingLookup.get(mapping);
if (handlerMethod != null && !handlerMethod.equals(newHandlerMethod)) {
throw new IllegalStateException(
"Ambiguous mapping. Cannot map '" + newHandlerMethod.getBean() + "' method \n" +
newHandlerMethod + "\nto " + mapping + ": There is already '" +
handlerMethod.getBean() + "' bean method\n" + handlerMethod + " mapped.");
}
}