关于springboot:SpringBoot源码mvc工作流程中

DispatcherServlet 解决流程

上一节讲了Spring容器启动，会把url与类办法的映射关系保存起来，这一节，就能看到它的作用啦。

DispatcherServlet是整个SpringMVC的外围，负责申请解决以及返回响应的工作。直奔主题，找到DispatcherServlet类，再找到该类下的doService()办法，要害代码：

try {
    doDispatch(request, response);
}

点击这个孤单的办法，进去，上外围马：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    // 定义handler执行链，重要
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;

    ModelAndView mv = null;
    // 查看是否是文件申请
    processedRequest = checkMultipart(request);
    multipartRequestParsed = (processedRequest != request);

    // 获取以后申请的handler
    mappedHandler = getHandler(processedRequest);
    if (mappedHandler == null) {
        noHandlerFound(processedRequest, response);
        return;
    }

    // 获取以后申请的适配器
    HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

    // 判断get办法是否有批改，没有间接返回
    String method = request.getMethod();
    boolean isGet = HttpMethod.GET.matches(method);
    if (isGet || HttpMethod.HEAD.matches(method)) {
        long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
        if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
         return;
        }
    }
    // 前置解决
    if (!mappedHandler.applyPreHandle(processedRequest, response)) {
        return;
    }

    // hander理论执行
    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

    applyDefaultViewName(processedRequest, mv);
    // handler后置解决
    mappedHandler.applyPostHandle(processedRequest, response, mv);
    // 解决散发后的后果
    processDispatchResult(processedRequest, response, mappedHandler, mv,     
                          dispatchException);

}

看到那个闪亮的办法没 – getHandler(processedRequest)，点击进去，下马：

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    if (this.handlerMappings != null) {
        for (HandlerMapping mapping : this.handlerMappings) {
            // 从handlerMappings 获取并构建申请的执行链
            HandlerExecutionChain handler = mapping.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
    }
    return null;
}

打个debug，看下handlerMappings外面是啥

看到没，这不就是上一节讲到的东东咩？

再点击 mapping.getHandler(request)办法进去，看看有啥：

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    // 获取handler
    Object handler = getHandlerInternal(request);
    ……
        
    // 是beanName获取对应的bean
    if (handler instanceof String) {
        String handlerName = (String) handler;
        handler = obtainApplicationContext().getBean(handlerName);
    }
    ……
        
    // 构建handler的执行链
    HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);    
    ……

    return executionChain;
}

getHandlerInternal(request) 是重点，点进去：

protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
    // 获取拜访门路，如 /test/hello
    String lookupPath = initLookupPath(request);
    this.mappingRegistry.acquireReadLock();
    try {
        // 查找拜访门路对应的解决办法
        HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
        return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
    }
    finally {
        this.mappingRegistry.releaseReadLock();
    }
}

快到了！持续点击 lookupHandlerMethod(lookupPath, request)，进入：

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
    List<Match> matches = new ArrayList<>();
    // 依据拜访门路匹配申请办法
    List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);
    if (directPathMatches != null) {
        // 依据找到的信息，封装 matches
        addMatchingMappings(directPathMatches, matches, request);
    }
    if (matches.isEmpty()) {
        addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);
    }
    
    // 省略查找最近匹配内容
    ……
    
    // 返回 handlerMethod
    request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.getHandlerMethod());
    handleMatch(bestMatch.mapping, lookupPath, request);
    return bestMatch.getHandlerMethod();
}

点击this.mappingRegistry.getMappingsByDirectPath(lookupPath)，进入：

public List<T> getMappingsByDirectPath(String urlPath) {
    return this.pathLookup.get(urlPath);
}

看到了没，pathLookup退场了，T 类型是 RequestMappingInfo。

这一步，就能找到 handlerMethod了，也就是拜访门路对应的解决办法。所以下面的getHandler() 办法就能返回对应的 HandlerExecutionChain。

回到 doDispatch()办法中，既然拿到了 handlerMethod，前面就是做了一些精益求精的事，最初调用该办法了。

不讲了，口渴，饮杯开水去~~