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跨域問題報錯：

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. 為了解決跨域問題，我在服務端代碼中加了個過濾器：

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;/*** 解決跨域設置* （可把此設置放在 nginx 中，但只能設置一處）** @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;// 此處 setHeader、addHeader 方法都可用。但 addHeader時寫多個會報錯：“...,but only one is allowed”// response.setHeader("Access-Control-Allow-Origin", "*");response.addHeader("Access-Control-Allow-Origin", request.getHeader("origin"));// 解決預請求（發送2次請求），此問題也可在 nginx 中作相似設置解決。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. 同時在 nginx 中也作了相關配置：

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.?運行報錯如題。

4. 解決：此錯表示設置重復，只允許設置一種，去除多余設置，保留一種即可。選擇第1點中方法，或者第2點中方法都可以。

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跨域相關知識點解說：?https://blog.csdn.net/jiangyu1013/article/details/84315748

PS 跨域問題解決也見文章 ：解決跨域問題：No 'Access-Control-Allow-Origin' header is present on the requested resource.

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