spring MVC cors跨域实现源码解析

<filter>
 <filter-name>cors</filter-name>
 <filter-class>org.springframework.web.filter.CorsFilter</filter-class>
</filter>
<filter-mapping>
 <filter-name>cors</filter-name>
 <url-pattern>/*</url-pattern>
</filter-mapping>

// 简单配置，未配置的均使用默认值，就是全面放开
<mvc:cors> 
 <mvc:mapping path="/**" /> 
</mvc:cors> 
// 这是一个全量配置
<mvc:cors> 
 <mvc:mapping path="/api/**" 
  allowed-origins="http://domain1.com, http://domain2.com" 
  allowed-methods="GET, PUT" 
  allowed-headers="header1, header2, header3" 
  exposed-headers="header1, header2" allow-credentials="false" 
  max-age="123" /> 
  <mvc:mapping path="/resources/**" 
  allowed-origins="http://domain1.com" /> 
</mvc:cors> 

@CrossOrigin(maxAge = 3600) 
@RestController 
@RequestMapping("/account") 
public class AccountController { 
 @CrossOrigin("http://domain2.com") 
 @RequestMapping("/{id}") 
 public Account retrieve(@PathVariable Long id) { 
  // ... 
 } 
} 

 // CorsConfiguration
 public static final String ALL = "*";
 // 允许的请求源
 private List<String> allowedOrigins;
 // 允许的http方法
 private List<String> allowedMethods;
 // 允许的请求头
 private List<String> allowedHeaders;
 // 返回的响应头
 private List<String> exposedHeaders;
 // 是否允许携带cookies
 private Boolean allowCredentials;
 // 预请求的存活有效期
 private Long maxAge;

// CorsBeanDefinitionParser
if (mappings.isEmpty()) {
 // 最简配置时的默认设置
 CorsConfiguration config = new CorsConfiguration();
 config.setAllowedOrigins(DEFAULT_ALLOWED_ORIGINS);
 config.setAllowedMethods(DEFAULT_ALLOWED_METHODS);
 config.setAllowedHeaders(DEFAULT_ALLOWED_HEADERS);
 config.setAllowCredentials(DEFAULT_ALLOW_CREDENTIALS);
 config.setMaxAge(DEFAULT_MAX_AGE);
 corsConfigurations.put("/**", config);
}else {
 // 单个mapping的处理
 for (Element mapping : mappings) {
  CorsConfiguration config = new CorsConfiguration();
  if (mapping.hasAttribute("allowed-origins")) {
   String[] allowedOrigins = StringUtils.tokenizeToStringArray(mapping.getAttribute("allowed-origins"), ",");
   config.setAllowedOrigins(Arrays.asList(allowedOrigins));
  }
  // ...
 }

// MvcNamespaceUtils
 public static RuntimeBeanReference registerCorsConfigurations(Map<String, CorsConfiguration> corsConfigurations, ParserContext parserContext, Object source) {
  if (!parserContext.getRegistry().containsBeanDefinition(CORS_CONFIGURATION_BEAN_NAME)) {
   RootBeanDefinition corsConfigurationsDef = new RootBeanDefinition(LinkedHashMap.class);
   corsConfigurationsDef.setSource(source);
   corsConfigurationsDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
   if (corsConfigurations != null) {
    corsConfigurationsDef.getConstructorArgumentValues().addIndexedArgumentValue(0, corsConfigurations);
   }
   parserContext.getReaderContext().getRegistry().registerBeanDefinition(CORS_CONFIGURATION_BEAN_NAME, corsConfigurationsDef);
   parserContext.registerComponent(new BeanComponentDefinition(corsConfigurationsDef, CORS_CONFIGURATION_BEAN_NAME));
  }
  else if (corsConfigurations != null) {
   BeanDefinition corsConfigurationsDef = parserContext.getRegistry().getBeanDefinition(CORS_CONFIGURATION_BEAN_NAME);   corsConfigurationsDef.getConstructorArgumentValues().addIndexedArgumentValue(0, corsConfigurations);
  }
  return new RuntimeBeanReference(CORS_CONFIGURATION_BEAN_NAME);
 }

// RequestMappingHandlerMapping
 @Override
 protected CorsConfiguration initCorsConfiguration(Object handler, Method method, RequestMappingInfo mappingInfo) {
  HandlerMethod handlerMethod = createHandlerMethod(handler, method);
  CrossOrigin typeAnnotation = AnnotatedElementUtils.findMergedAnnotation(handlerMethod.getBeanType(), CrossOrigin.class);
  CrossOrigin methodAnnotation = AnnotatedElementUtils.findMergedAnnotation(method, CrossOrigin.class);
  if (typeAnnotation == null && methodAnnotation == null) {
   return null;
  }
  CorsConfiguration config = new CorsConfiguration();
  updateCorsConfig(config, typeAnnotation);
  updateCorsConfig(config, methodAnnotation);
  // ... 设置默认值
  return config;
 } 

 // UrlBasedCorsConfigurationSource
 public CorsConfiguration getCorsConfiguration(HttpServletRequest request) {
  String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
  for(Map.Entry<String, CorsConfiguration> entry : this.corsConfigurations.entrySet()) {
   if (this.pathMatcher.match(entry.getKey(), lookupPath)) {
    return entry.getValue();
   }
  }
  return null;
 }
 // AbstractHandlerMapping
 public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
  Object handler = getHandlerInternal(request);
  // ...
  HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
  if (CorsUtils.isCorsRequest(request)) {
   CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
   CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
   CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
   executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
  }
  return executionChain;
 }
 // HttpHeaders
 public static final String ORIGIN = "Origin";
 // CorsUtils
 public static boolean isCorsRequest(HttpServletRequest request) {
  return (request.getHeader(HttpHeaders.ORIGIN) != null);
 }

 // AbstractHandlerMapping
 protected HandlerExecutionChain getCorsHandlerExecutionChain(HttpServletRequest request,
   HandlerExecutionChain chain, CorsConfiguration config) {
  if (CorsUtils.isPreFlightRequest(request)) {
   HandlerInterceptor[] interceptors = chain.getInterceptors();
   chain = new HandlerExecutionChain(new PreFlightHandler(config), interceptors);
  }
  else {
   chain.addInterceptor(new CorsInterceptor(config));
  }
  return chain;
 }
 private class PreFlightHandler implements HttpRequestHandler {
  private final CorsConfiguration config;
  public PreFlightHandler(CorsConfiguration config) {
   this.config = config;
  }
  @Override
  public void handleRequest(HttpServletRequest request, HttpServletResponse response)
    throws IOException {

   corsProcessor.processRequest(this.config, request, response);
  }
 }
 private class CorsInterceptor extends HandlerInterceptorAdapter {
  private final CorsConfiguration config;
  public CorsInterceptor(CorsConfiguration config) {
   this.config = config;
  }
  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
    Object handler) throws Exception {

   return corsProcessor.processRequest(this.config, request, response);
  }
 }
 // CorsUtils
 public static boolean isPreFlightRequest(HttpServletRequest request) {
  return (isCorsRequest(request) && request.getMethod().equals(HttpMethod.OPTIONS.name()) &&
    request.getHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD) != null);
 }