No 'Access-Control-Allow-Origin' header is present on the requested resource 是跨域的问题吗？

Access to XMLHttpRequest at 'http://localhost:8031/employee/findEmployeeList' from origin 'http://localhost:8080' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

因为java代码中启用了验证；

放开Employee的，让前端访问就没问题了，可是前端请求：不能访问 和能访问都间隔一次，是为什么？这是个问题；