Javascript fetch调用后端两次[重复]

Question

我有后端应用程序写在java ee和泽西。当我使用JavaScript Fetch API将数据发送到restendpoint时，我看到过滤器被激发了两次。一旦它没有授权头，第二个它有。当我尝试从web浏览器打开我的网站时，这个过滤器只被调用一次。为什么会发生这种事。也许是因为CORS？

下面我的日志从单一的帖子，两个打印从同一个过滤器。

 http://localhost:8080/BlogRest/controller/endpoint/|#]
  Key=host, value=localhost:8080|#]
  Key=origin, value=http://localhost:3000|#]
  Key=access-control-request-method, value=POST|#]
  Key=content-length, value=0|#]
  Key=access-control-request-headers, value=authorization,content-type|#]
  Key=connection, value=keep-alive|#]
  Key=accept, value=*/*|#]
  Key=user-agent, value=user agent data|#]
  Key=referer, value=http://localhost:3000/|#]
  Key=accept-language, value=pl-pl|#]
  Key=accept-encoding, value=gzip, deflate|#]
  

第二次通话

  http://localhost:8080/BlogRest/controller/endpoint/|#]
  Key=host, value=localhost:8080|#]
  Key=origin, value=http://localhost:3000|#]
  Key=content-type, value=application/json|#]
  Key=accept-language, value=pl-pl|#]
  Key=accept-encoding, value=gzip, deflate|#]
  Key=connection, value=keep-alive|#]
  Key=accept, value=*/*|#]
  Key=user-agent, value=user agent data|#]
  Key=authorization, value=Bearer token|#]
  Key=referer, value=http://localhost:3000/origin|#]
  Key=content-length, value=15|#]

Answer 1

有两个请求是因为CORS。一个请求方法是OPTIONS，当它被预成形时，就会启动预期的POST请求。选项请求不调用endpoint，它只获取te服务器配置。因此，我使用HttpServletRequest getMethod（）按方法在Java过滤器请求中进行了过滤。

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest requ = (HttpServletRequest) request;

        if (requ.getMethod().toLowerCase().equals(HttpMethod.OPTIONS)) {
            chain.doFilter(request, response);
            return;
        }

        //do something on not options method.            

        chain.doFilter(request, response);

    }