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跨域问题报错：

Access to XMLHttpRequest at 'http://xx.xx.xx.xx/getUser' from origin 
'http://ergouzi.fun' has been blocked by CORS policy: 
The 'Access-Control-Allow-Origin' header contains multiple values 
'http://ergouzi.fun, *, http://ergouzi.fun', but only one is allowed.

1. 为了解决跨域问题，我在服务端代码中加了个过滤器：

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;/*** 解决跨域设置* （可把此设置放在 nginx 中，但只能设置一处）** @author silence* @date 2018/12/11 15:19*/@WebFilter(filterName = "requestFilter", urlPatterns = {"/*"})
public class RequestFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {HttpServletResponse response = (HttpServletResponse) servletResponse;HttpServletRequest request = (HttpServletRequest) servletRequest;// 此处 setHeader、addHeader 方法都可用。但 addHeader时写多个会报错：“...,but only one is allowed”// response.setHeader("Access-Control-Allow-Origin", "*");response.addHeader("Access-Control-Allow-Origin", request.getHeader("origin"));// 解决预请求（发送2次请求），此问题也可在 nginx 中作相似设置解决。response.setHeader("Access-Control-Allow-Headers", "x-requested-with,Cache-Control,Pragma,Content-Type,Token, Content-Type");response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");response.setHeader("Access-Control-Max-Age", "3600");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);}}@Overridepublic void destroy() {}}

2. 同时在 nginx 中也作了相关配置：

add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, DELETE';
add_header 'Access-Control-Allow-Headers' 'Content-Type';
...

3. 运行报错如题。

4. 解决：此错表示设置重复，只允许设置一种，去除多余设置，保留一种即可。选择第1点中方法，或者第2点中方法都可以。

 

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跨域相关知识点解说： https://blog.csdn.net/jiangyu1013/article/details/84315748

PS 跨域问题解决也见文章 ：解决跨域问题：No 'Access-Control-Allow-Origin' header is present on the requested resource.