后端如何处理跨域

1. 使用@CrossOrigin注解：
   可以为Controller中的方法添加@CrossOrigin注解来允许来自特定源(或所有源)的跨域请求。例如：

   @RestController
   public class MyController {
   
     @RequestMapping("/hello")
     @CrossOrigin(origins = "http://localhost:8080")
     public String hello() {
        return "Hello World!";
     }
   }

2. 配置WebMvcConfigurer：
   在WebMvcConfigurer中配置addCorsMappings()方法，它会将跨域配置应用于整个应用程序。例如：

   @Configuration
   public class WebConfig implements WebMvcConfigurer {
   
      @Override
      public void addCorsMappings(CorsRegistry registry) {
         registry.addMapping("/**")
            .allowedOrigins("http://localhost:8080")
            .allowedMethods("GET", "POST", "PUT", "DELETE");
      }
   }

3. 使用Filter过滤器：
   实现一个CorsFilter类并继承OncePerRequestFilter类。然后在doFilterInternal方法中设置跨域头。例如：

   public class CorsFilter extends OncePerRequestFilter {
   
      @Override
      protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
   
         response.setHeader("Access-Control-Allow-Origin", "http://localhost:8080");
         response.setHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE");
         response.setHeader("Access-Control-Allow-Headers", "Content-Type");
         response.setHeader("Access-Control-Max-Age", "1800");
   
         filterChain.doFilter(request, response);
      }
   }