解决axios跨域请求报错No 'Access-Control-Allow-Origin' header is present on the requested resource.（学习记录）

原因是请求头中缺少设置
一个有效的解决办法是在后台写一个过滤器，
不要忘了在web.xml中配置这个过滤器
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**

• @Author:jagger
  **/
  public class CorsFilter implements Filter {
  @Override
  public void init(FilterConfig filterConfig) throws ServletException {

  }

  @Override
  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
  HttpServletResponse response = (HttpServletResponse) servletResponse;
  HttpServletRequest request = (HttpServletRequest) servletRequest;

   String origin = request.getHeader("Origin");
   response.setHeader("Access-Control-Allow-Origin", origin);
   response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
   response.setHeader("Access-Control-Max-Age", "3600");
   response.setHeader("Access-Control-Allow-Headers", "x-requested-with,Authorization");
   response.setHeader("Access-Control-Allow-Credentials", "true");
   String method = request.getMethod();
   if (method.equalsIgnoreCase("OPTIONS")) {
       servletResponse.getOutputStream().write("Success".getBytes("utf-8"));
   } else {
       filterChain.doFilter(servletRequest, servletResponse);
   }
  

  }

  @Override
  public void destroy() {

  }
  }