解决Request header field XXX is not allowed by access

解决Request header field XXX is not allowed by access

问题

Access to XMLHttpRequest at ‘B/path/a’ from origin ‘A’ has been blocked by CORS policy: Request header field AC-User-Agent is not allowed by Access-Control-Allow-Headers in preflight response.

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产生原因

前后端分离项目，由于老版本项目没有接入网关和微服务，因此需要通过域名加接口地址的方式来直接访问，因此出现以下情况：

网站主域名是A，老接口服务的域名是B。 在调用老接口服务时，要求前端在header里必须加上AC-User-Agent字段，用于实现老接口业务 在这种情况下，前端在A网站上调用B，由此产生上述问题

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解决方法

由于是跨域调用B接口时，未允许使用请求头AC-User-Agent（Request header field AC-User-Agent is not allowed by Access-Control-Allow-Headers），因此需要在B的Java代码里面新建一个过滤器，在过滤器中设置AC-User-Agent为合法请求头

@WebFilter("/*") 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 resp = (HttpServletResponse) servletResponse; HttpServletRequest req = (HttpServletRequest) servletRequest; String origin = req.getHeader("Origin"); resp.setHeader("Access-Control-Allow-Origin", origin); resp.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS"); resp.setHeader("Access-Control-Allow-Headers", "AC-User-Agent, token, content-type"); resp.setHeader("Access-Control-Allow-Credentials", "true"); filterChain.doFilter(servletRequest, servletResponse); } @Override public void destroy() { } }