内容概览
- 初始化HandlerMapping
- 根据request获取对应的HandlerExecutionChain
- RequestMappingHandlerMapping体系实现获取HandlerExecutionChain
初始化HandlerMapping
前面注册RequestMapping和Handler的映射关系时声明的RequestMappingHandlerMapping就是HandlerMapping的一个实现。该接口中定义了一个方法getHandler就是返回当前请求的Handler或者拦截器。这个匹配的过程可能取决于请求的URL、session的状态或者其他的原因，由具体的实现决定。如果找到匹配结果就会返回一个HandlerExecutionChain对象，HandlerExecutionChain封装了Handler和拦截器。
/**
* Return a handler and any interceptors for this request.
*/
@Nullable
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
DispatcherServlet的initHandlerMappings
在DispatcherServlet类中的initHandlerMappings就是获取上下文中的HandlerMapping。这里做了简化没有对获取不到使用默认策略进行展示。
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
//Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
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.
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
根据request获取对应的HandlerExecutionChain
现在的DispatcherServlet已经匹配了所有的Http请求，并且交给方法doDispatch方法去处理，因此在该方法中首先就是获取当前请求的Handler。
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = getHandler(processedRequest);
if (null == mappedHandler) {
noHandlerFound(processedRequest, response);
return;
}
}
/**
* Return the HandlerExecutionChain for this request.
*/
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (null != this.handlerMappings) {
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (null != handler) {
return handler;
}
}
}
return null;
}
这两小块代码就是获取Handler的主干，具体详细的获取操作交给HandlerMapping的实现体系。
RequestMappingHandlerMapping体系实现获取HandlerExecutionChain
RequestMappingHandlerMapping类结构图
根据请求获取Handler的流程图
AbstractHandlerMapping的getHandler方法
@Override
public HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = getHandlerInternal(request);
return getHandlerExecutionChain(handler, request);
}
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
return handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler :
new HandlerExecutionChain(handler);
}
DispatcherServlet中会调用getHandler方法。AbstractHandlerMapping实现了HandlerMapping的getHandler方法，然后调用模版方法getHandlerInternal获取当前请求匹配的handler。最后将获取到的Handler包装成HandlerExecutionChain。
AbstractHandlerMethodMapping实现的getHandlerInternal
@Override
@Nullable
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
String lookupPath = initLookupPath(request);
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
return null != handlerMethod ? handlerMethod.createWithResolvedBean() : null;
}
- 首先调用父类方法initLookupPath获取当前请求的URL，实际上调用的是UrlPathHelper类中的方法。
- 然后调用lookupHandlerMethod根据请求URL获取最佳匹配的HandlerMethod
- 最后就是返回HandlerMethod或者null
AbstractHandlerMethodMapping的lookupHandlerMethod方法
/**
* Look up the best-matching handler method for the current request. If multiple
* matches are found, the best match is selected.
*/
@Nullable
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
//1.根据请求URL获取RequestMappingInfo
List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);
if (null != directPathMatches) {
//2.从RequestMappingInfo中构造Match放到matches中
addMatchingMapping(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
addMatchingMapping(this.mappingRegistry.getRegistration().keySet(), matches, request);
}
//3.获取最佳匹配的结果
if (!matches.isEmpty()) {
Match bestMatch = matches.get(0);
request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.getHandlerMethod());
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.getHandlerMethod();
} else {
//返回没有匹配的结果
return handleNoMatch(this.mappingRegistry.getRegistration().keySet(), lookupPath, request);
}
}
private void addMatchingMapping(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {
for (T mapping : mappings) {
T match = getMatchingMapping(mapping, request);
if (null != match) {
matches.add(new Match(match, this.mappingRegistry.getRegistration().get(mapping)));
}
}
}
- this.mappingRegistry是AbstractHandlerMethodMapping的内部类MappingRegistry，MappingRegistry维护了请求URL和RequestMappingInfo的关系。这个后面专门描述一下这个关系的创建及获取过程，这里只要知道是根据请求的URL从map中获取匹配的RequestMappingInfo即可。
- 遍历匹配的RequestMappingInfo并从中构造Match放到matches中，遍历的过程会调用模版方法getMatchingMapping
- 这里是获取最佳匹配的结果，这里简化了，实际上会进行compare获取最优的一个
- 如果没有匹配的则返回对应的标识
RequestMappingInfoHandlerMapping的getMatchingMapping
@Override
protected RequestMappingInfo getMatchingMapping(RequestMappingInfo info, HttpServletRequest request) {
return info.getMatchingCondition(request);
}
这里只能说RequestMappingInfo维护了获取的逻辑。也留到RequestMappingInfo里一起描述吧。
测试
调用example-easy-spring中的测试接口
DispatcherServlet中断点查看
在DispatcherServlet中getHandler方法调用后面断点，可以看到获取到了beanController中的beans方法
