1、相关组件

2、cors注册

CorsRegistry：作为cors注册者，管理跨域配置。

CorsRegistration：作为Cors的注册项，包含路径模式及对应的跨域配置

CorsConfigurationSource：作为cors配置的提供者接口

UrlBaseCorsConfigurationSource：是CorsConfigurationSource的一个具体实现

3、Cors处理

4、spring mvc中cors的初始化及运行

4.1 初始化

通过WebMvcConfigurer.addCorsMappings添加自定义跨域配置。因为在DelegatingWebMvcConfiguration配置中初始化时会添加自定义的WebMvcConfigurer放入到WebMvcConfigurerComposite中。

//DelegatingWebMvcConfiguration
private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();@Autowired(required = false)public void setConfigurers(List<WebMvcConfigurer> configurers) {if (!CollectionUtils.isEmpty(configurers)) {this.configurers.addWebMvcConfigurers(configurers);}}protected void addCorsMappings(CorsRegistry registry) {this.configurers.addCorsMappings(registry);}

在WebMvcConfigurationSupport中的requestMappingHandlerMapping中获取cors配置，并且设置到RequestMappingHandlerMapping中

public RequestMappingHandlerMapping requestMappingHandlerMapping(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();mapping.setOrder(0);mapping.setInterceptors(getInterceptors(conversionService, resourceUrlProvider));mapping.setContentNegotiationManager(contentNegotiationManager);mapping.setCorsConfigurations(getCorsConfigurations());PathMatchConfigurer pathConfig = getPathMatchConfigurer();if (pathConfig.getPatternParser() != null) {mapping.setPatternParser(pathConfig.getPatternParser());}else {mapping.setUrlPathHelper(pathConfig.getUrlPathHelperOrDefault());mapping.setPathMatcher(pathConfig.getPathMatcherOrDefault());Boolean useSuffixPatternMatch = pathConfig.isUseSuffixPatternMatch();if (useSuffixPatternMatch != null) {mapping.setUseSuffixPatternMatch(useSuffixPatternMatch);}Boolean useRegisteredSuffixPatternMatch = pathConfig.isUseRegisteredSuffixPatternMatch();if (useRegisteredSuffixPatternMatch != null) {mapping.setUseRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch);}}Boolean useTrailingSlashMatch = pathConfig.isUseTrailingSlashMatch();if (useTrailingSlashMatch != null) {mapping.setUseTrailingSlashMatch(useTrailingSlashMatch);}if (pathConfig.getPathPrefixes() != null) {mapping.setPathPrefixes(pathConfig.getPathPrefixes());}return mapping;}protected final Map<String, CorsConfiguration> getCorsConfigurations() {if (this.corsConfigurations == null) {CorsRegistry registry = new CorsRegistry();addCorsMappings(registry);this.corsConfigurations = registry.getCorsConfigurations();}return this.corsConfigurations;}

4.2 运行时

在运行时，在获取HandlerExecutionChain时，会判断是否有跨域配置源，如果有，判断请求是否是preflight请求，则创建包含PreFlightHandler的执行链，否则就在执行链中添加跨域请求拦截器，拦截器通过CrosProcessor处理请求。

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {Object handler = getHandlerInternal(request);if (handler == null) {handler = getDefaultHandler();}if (handler == null) {return null;}// Bean name or resolved handler?if (handler instanceof String) {String handlerName = (String) handler;handler = obtainApplicationContext().getBean(handlerName);}HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);if (logger.isTraceEnabled()) {logger.trace("Mapped to " + handler);}else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {logger.debug("Mapped to " + executionChain.getHandler());}if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) {CorsConfiguration config = getCorsConfiguration(handler, request);if (getCorsConfigurationSource() != null) {CorsConfiguration globalConfig = getCorsConfigurationSource().getCorsConfiguration(request);config = (globalConfig != null ? globalConfig.combine(config) : config);}if (config != null) {config.validateAllowCredentials();}executionChain = getCorsHandlerExecutionChain(request, executionChain, config);}return executionChain;}protected HandlerExecutionChain getCorsHandlerExecutionChain(HttpServletRequest request,HandlerExecutionChain chain, @Nullable CorsConfiguration config) {if (CorsUtils.isPreFlightRequest(request)) {HandlerInterceptor[] interceptors = chain.getInterceptors();return new HandlerExecutionChain(new PreFlightHandler(config), interceptors);}else {chain.addInterceptor(0, new CorsInterceptor(config));return chain;}}private class PreFlightHandler implements HttpRequestHandler, CorsConfigurationSource {@Nullableprivate final CorsConfiguration config;public PreFlightHandler(@Nullable CorsConfiguration config) {this.config = config;}@Overridepublic void handleRequest(HttpServletRequest request, HttpServletResponse response) throws IOException {corsProcessor.processRequest(this.config, request, response);}@Override@Nullablepublic CorsConfiguration getCorsConfiguration(HttpServletRequest request) {return this.config;}}private class CorsInterceptor implements HandlerInterceptor, CorsConfigurationSource {@Nullableprivate final CorsConfiguration config;public CorsInterceptor(@Nullable CorsConfiguration config) {this.config = config;}@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {// Consistent with CorsFilter, ignore ASYNC dispatchesWebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);if (asyncManager.hasConcurrentResult()) {return true;}return corsProcessor.processRequest(this.config, request, response);}@Override@Nullablepublic CorsConfiguration getCorsConfiguration(HttpServletRequest request) {return this.config;}}

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