1. SpringMVC重要組件
1. DispatcherServlet
SpringMVC的中央Servlet，所有請求的入口，重寫了doService()方法。核心方法：doService()、doDispatch()。
2. HandlerMapping
處理器映射，負責根據HttpServletRequest找到對應的Handler，這裏返回Handler的輔助類HandlerExecutionChain。
public interface HandlerMapping {
@Nullable
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}3. HandlerExecutionChain
Handler execution chain, consisting of handler object and any handler interceptors.
處理器執行鏈，Handler輔助類，由Handler對象和一些HandlerInterceptor組成，主要功能爲執行攔截器，核心屬性和方法：
private final Object handler;
private HandlerInterceptor[] interceptors;
// 一般情況下返回的是一個HandlerMethod對象
Object getHandler()
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response)
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv)4. HandlerMethod
Encapsulates information about a handler method consisting of a method and a bean. Provides convenient access to method parameters, the method return value, method annotations, etc.
保存了Controller Bean對象和對應的Method對象。
// 對應的Controller實例
private final Object bean;
// 處理請求的方法
private final Method method;
// 方法的參數
private final MethodParameter[] parameters;5. HandlerInterceptor
攔截器，自定義攔截器實現此接口。preHandle()和postHandle()方法分別在實際的請求處理之前和之後執行。
public interface HandlerInterceptor {
default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return true;
}
default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
@Nullable ModelAndView modelAndView) throws Exception {
}
default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
@Nullable Exception ex) throws Exception {
}
}6. HandlerAdapter
處理器適配器。handle()方法負責執行實際的請求處理並返回一個ModelAndView對象。
public interface HandlerAdapter {
boolean supports(Object handler);
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
long getLastModified(HttpServletRequest request, Object handler);
}2. SpringMVC請求處理流程
- DispatcherServlet作爲入口且重寫了doService()方法，所以請求會首先到doService()方法。下面步驟1、2、3在doService()方法完成，接着doService()方法調用doDispatch()方法，doDispatch()方法完成剩下的所有步驟。
- WebApplicationContext對象綁定到Request，key爲DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE。
- locale resolver綁定到Request。
- theme resolver綁定到Request。
- 如果是multipart request，包裝成MultipartHttpServletRequest。
- 調用HandlerMapping的getHandler()方法獲取對應的Handler，這裏是HandlerExecutionChain對象。
- 調用HandlerExecutionChain的getHandler()方法，這裏返回HandlerMethod對象，根據Handler獲取HandlerAdapter。
- 如果是GET或者HEAD方法執行HandlerAdapter的getLastModified()方法。
- 調用HandlerExecutionChain的applyPreHandle()方法執行HandlerInterceptor的preHandle()方法。
- 調用HandlerAdapter的handle()方法執行實際的請求處理，實際執行HandlerMethod的對應方法，返回ModelAndView對象，
- 根據ModelAndView視圖解析器找到對應的View。
- 渲染視圖返回用戶。
3. HandlerMethod收集
請求處理流程中的第5步中提到了HandlerMapping，這個核心第實現是RequestMappingHandlerMapping類，當使用SpringMVC時此類就會被注入到spring容器中，此類實現了InitializingBean接口，所以在實例化過程中會執行afterPropertiesSet()方法，此方法調用initHandlerMethods()，這個方法負責收集HandlerMethod，其相關源碼如下：
/**
* Detects handler methods at initialization.
* @see #initHandlerMethods
*/
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}
/**
* Scan beans in the ApplicationContext, detect and register handler methods.
* @see #getCandidateBeanNames()
* @see #processCandidateBean
* @see #handlerMethodsInitialized
*/
protected void initHandlerMethods() {
// 1. 遍歷所有beanName
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
processCandidateBean(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
/**
* 2. 判斷beanName對應的Class是否爲Controller
*/
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);
}
}
// 3. 判斷邏輯爲是否有@Controller或@RequestMapping註解
if (beanType != null && isHandler(beanType)) {
// 檢測Controller類中的HandlerMethod
detectHandlerMethods(beanName);
}
}
@Override
protected boolean isHandler(Class<?> beanType) {
// 判斷邏輯爲是否有@Controller或@RequestMapping註解
return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}
protected void detectHandlerMethods(Object handler) {
Class<?> handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
Class<?> userType = ClassUtils.getUserClass(handlerType);
// 4. 檢測到所有Method
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("Mapped " + methods.size() + " handler method(s) for " + userType + ": " + methods);
}
// 5. 對檢測到到Method進行註冊緩存。
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
// 這裏把解析出到HanderMethod對象進行組冊
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
// 6. 這裏組冊到MappingRegistry的對應的集合中緩存起來
this.mappingRegistry.register(mapping, handler, method);
}相關類圖：