HandlerMapping机制

HandlerMapping是SpringMVC请求分发的核心组件，负责建立请求与处理器之间的映射关系。

核心接口定义

public interface HandlerMapping {
    @Nullable
    HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}

主要实现类

工作流程

1. 初始化阶段

// RequestMappingHandlerMapping 初始化
public void afterPropertiesSet() {
    // 扫描所有带@Controller和@RequestMapping注解的Bean
    initHandlerMethods();
}

protected void initHandlerMethods() {
    // 获取所有候选Bean
    String[] beanNames = obtainApplicationContext()
        .getBeanNamesForType(Object.class);
    for (String beanName : beanNames) {
        // 检测并注册HandlerMethod
        detectHandlerMethods(beanName);
    }
}

2. 请求映射注册

protected void registerHandlerMethod(Object handler, Method method,
                                      RequestMappingInfo mapping) {
    // 创建HandlerMethod并注册到MappingRegistry
    HandlerMethod handlerMethod = createHandlerMethod(handler, method);
    mappingRegistry.register(mapping, handlerMethod, method);
}

3. 请求处理阶段

public HandlerExecutionChain getHandler(HttpServletRequest request) {
    // 遍历所有HandlerMapping
    for (HandlerMapping mapping : this.handlerMappings) {
        HandlerExecutionChain handler = mapping.getHandler(request);
        if (handler != null) {
            return handler;
        }
    }
    return null;
}

MappingRegistry核心结构

class MappingRegistry {
    // URL路径 -> MappingRegistration
    private final MultiValueMap<String, RequestMappingInfo> urlLookup =
        new LinkedMultiValueMap<>();

    // RequestMappingInfo -> HandlerMethod
    private final Map<RequestMappingInfo, HandlerMethod> mappingLookup =
        new LinkedHashMap<>();

    // 方法名 -> RequestMappingInfo
    private final Map<String, List<RequestMappingInfo>> nameLookup =
        new ConcurrentHashMap<>();
}

RequestMappingInfo构建

// 从@RequestMapping注解构建映射信息
private RequestMappingInfo createRequestMappingInfo(
        RequestMapping requestMapping) {
    return RequestMappingInfo
        .paths(resolveEmbeddedValuesInPatterns(requestMapping.path()))
        .methods(requestMapping.method())
        .params(requestMapping.params())
        .headers(requestMapping.headers())
        .consumes(requestMapping.consumes())
        .produces(requestMapping.produces())
        .build();
}

拦截器集成

public HandlerExecutionChain getHandler(HttpServletRequest request) {
    // 获取HandlerMethod
    HandlerMethod handler = getHandlerInternal(request);
    if (handler == null) {
        return null;
    }
    // 创建执行链，添加拦截器
    HandlerExecutionChain chain = new HandlerExecutionChain(handler);
    chain.addInterceptors(getAdaptedInterceptors());
    return chain;
}

HandlerMapping通过MappingRegistry维护URL到Handler的映射关系，支持ant风格路径匹配和精确匹配。

要点总结

1. HandlerMapping负责URL到Handler的映射解析
2. RequestMappingHandlerMapping是主要实现，处理@RequestMapping注解
3. MappingRegistry是核心数据结构，存储映射关系
4. 支持多条件匹配：路径、方法、参数、请求头等
5. 返回HandlerExecutionChain包含Handler和拦截器链

jwdev/articles/SPRINGMVC/专家/MVC核心源码执行流程/MVC核心源码执行流程/HandlerMapping机制.md