如何解決跨域問題，以及跨域預檢未通過問題

has been blocked by CORS policy: Response to preflight request doesn’t pass access control check: It does not have HTTP ok status.

最近在前后端聯調時，當我通過axios在前端進行POST請求時，瀏覽器報如下錯誤：

has been blocked by CORS policy: Response to preflight request doesn’t pass access control check: It does not have HTTP ok status.

乍一看是跨域問題，但其實並不是跨域問題。由於瀏覽器將CORS請求分為兩類：簡單請求（simple request）和非簡單請求（not-simple-request）。非簡單請求 會在正式通信之前，增加一次HTTP請求，稱之為預檢請求。瀏覽器會先發起OPTIONS方法到服務器，以獲知服務器是否允許該實際請求。

這是在第一次預請求時候沒有請求成功，預請求不成功。

先聊一下在SpringBoot項目中如何處理跨域問題：添加如下代碼：

@Component
public class SimpleCORSFilter implements Filter {

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) res;
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE, HEAD,PUT");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Headers", "access-control-allow-origin, authority, content-type, version-info, X-Requested-With");
        chain.doFilter(req, res);
    }

    @Override
    public void init(FilterConfig filterConfig) {}

    @Override
    public void destroy() {}

}

其次如何解決has been blocked by CORS policy: Response to preflight request doesn’t pass access control check: It does not have HTTP ok status.這個錯誤

@Component
public class SimpleCORSFilter implements Filter {

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) res;
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE, HEAD,PUT");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Headers", "access-control-allow-origin, authority, content-type, version-info, X-Requested-With");
        HttpServletRequest request = (HttpServletRequest)req;
        if ("OPTIONS".equals(request.getMethod())) {
            response.setStatus(HttpServletResponse.SC_OK);
            return;
        }

        chain.doFilter(req, res);
    }

    @Override
    public void init(FilterConfig filterConfig) {}

    @Override
    public void destroy() {}

}