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我的解决方法是后端加一个过滤器：

package gentle.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * 改写所有请求头
 * @author silence
 * @date 2018/12/11 15:19
 */

@WebFilter(filterName = "requestFilter",urlPatterns = {"/*"})
public class RequestFilter 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;

        response.setHeader("Access-Control-Allow-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-Headers", "Content-Type,XFILENAME,XFILECATEGORY,XFILESIZE,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() {

    }

}

重点是这行代码：

 response.setHeader("Access-Control-Allow-Origin", "*");

 方法二：前端也加头信息解决。

方法参见：https://www.cnblogs.com/Tohold/p/9173137.html