SpringMVC之源码分析--HandlerMapping（六）

yangxiaobo

2019-06-27

概述

上一节我们分析了RequestMappingHandlerMapping的初始化过程，即创建并注册HandlerMehtod，本章我们分析下RequestMappingHandlerMapping的请求处理过程，即查找HandlerMethod。

本系列文章是基于Spring5.0.5RELEASE。

总体流程

流程描述：

用户请求到达前端控制器DispatcherServlet.doDispatch方法
在doDispatch方法中调用本类的getHandler方法
getHandler方法调用HandlerMapping的getHandler方法
HandlerMapping.getHandler方法由抽象类AbstractHandlerMapping实现，故最终调用AbstracthandlerMapping.getHandler方法
在AbstractHandlerMapping的getHandler方法中调用钩子函数getHandlerInternal方法，该方法由子类AbstractHandlerMethodMapping实现
最终由AbstracthandlerMethodMapping.getHandlerInternal返回处理器方法即HandlerMethod
HandlerMethod代表查找到的处理请求Controller中的方法
返回给AbstractHandlerMapping，最终由其将处理器方法和拦截器组装成HandlerExectionChain对象返回

源码分析

DispatcherServlet

处理用户请求的方法到达doDispatch方法，源码如下：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    // ... ...
    
    //查找请求的处理器
    mappedHandler = getHandler(processedRequest);
    if (mappedHandler == null) {
        // 未找到处理器时跑异常
        noHandlerFound(processedRequest, response);
        return;
    }

    // ... ...
}

@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    if (this.handlerMappings != null) {
        // 迭代Spring支持的HandlerMapping，即我们配置或默认的HandlerMapping
        for (HandlerMapping hm : this.handlerMappings) {
            if (logger.isTraceEnabled()) {
                logger.trace(
                        "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
            }
            // 查找请求的处理器HandlerExecutionChain，包括请求需要的拦截器
            HandlerExecutionChain handler = hm.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
    }
    return null;
}

AbstractHandlerMethodMapping

提供查出处理器模板方法，具体实现由子类实现getHandlerInternal方法实现，代码如下：

@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    // 子类需实现getHandlerInternal方法，本例中由AbstractHandlerMethodMapping实现
    Object handler = getHandlerInternal(request);
    if (handler == null) {
        handler = getDefaultHandler();
    }
    if (handler == null) {
        return null;
    }
    // 如果handler是bean名字，则根据名字从上下文获取到处理类
    if (handler instanceof String) {
        String handlerName = (String) handler;
        handler = obtainApplicationContext().getBean(handlerName);
    }
    // 返回请求处理的HandlerExecutionChain对象
    HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
    // 对跨域的处理
    if (CorsUtils.isCorsRequest(request)) {
        CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
        CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
        CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
        executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
    }
    return executionChain;
}

AbstractHandlerMethodMapping

本类主要提供创建并注册HandlerMethod以及查找HandlerMethod功能，处理用户请求时，源码如下：

/**
 * 实现父类（AbstractHandlerMapping）的钩子函数
 */
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
    // 使用工具类UrlPathHelper，解析用户请求url
    String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
    if (logger.isDebugEnabled()) {
        logger.debug("Looking up handler method for path " + lookupPath);
    }
    this.mappingRegistry.acquireReadLock();
    try {
        // 查找HandlerMethod核心方法
        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 + "]");
            }
        }
        return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
    }
    finally {
        this.mappingRegistry.releaseReadLock();
    }
}

/**
 * 查找当前请求的处理器方法
 */
@Nullable
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
    // 定义匹配到的matches集合，其内存放匹配到的Match对象
    List<Match> matches = new ArrayList<>();
    // 根据请求url查找出RequestMappingInfo对象
    List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
    if (directPathMatches != null) {
        // 将查找到的RequestMappingInfo和处理器方法封装成Match对象存入到matches数组
        addMatchingMappings(directPathMatches, matches, request);
    }
    // 为查询到RequestMappingInfo时
    if (matches.isEmpty()) {
        // this.mappingRegistry.getMappings().keySet()--返回已注册所有的RequestMappingInfo
        // 查找到将RequestMappingInfo和处理器方法封装后存入matches数组
        addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
    }
    // 有匹配对象
    if (!matches.isEmpty()) {
        // 排序处理
        Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
        matches.sort(comparator);
        if (logger.isTraceEnabled()) {
            logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches);
        }
        // 取出Match，其封装了RequestMappingInfo和处理器方法
        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 + "}");
            }
        }
        // 主要是往Request的Attribute区放了些东西，具体啥用我也不懂
        handleMatch(bestMatch.mapping, lookupPath, request);
        // 返回处理器方法HandlerMethod
        return bestMatch.handlerMethod;
    }
    else {
        // 未找到处理
        return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
    }
}