uni-app中使用 uni.downloadfile下载文件报跨域错误和Refused to get unsafe header "content-disposition" 错-马育民老师

# 解决方式一

编写过滤器，对下载文件进行过滤，增加 **跨域 响应头**：

```
package top.malaoshi.netdisk.filter;

import top.malaoshi.util.StringUtil;

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

/**
 * 解决 使用 uni.download() 下载图片跨域的过滤器
 */
@WebFilter("/upload/*")
public class F0UploadFilter implements Filter {

@Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;
        String servletPath = req.getServletPath();
        String fileName = StringUtil.lastSlice(servletPath, "/", false);
        resp.setHeader("Access-Control-Allow-Origin","*");
        resp.setHeader("Access-Control-Allow-Methods","GET");
        /*
        设置Access-Control-Expose-Headers暴露Content-Disposition响应头
        否则uniapp下载时要获取Content-Disposition，导致出现Refused to get unsafe header错误
         */
        resp.setHeader("Access-Control-Expose-Headers", "Content-Disposition");
        // 对文件名进行编码，对于标准英文名来说，没有任何变化
        String fileNameEncode = URLEncoder.encode(fileName, "UTF-8");
        resp.addHeader("Content-Disposition", "attachment;filename=" + fileNameEncode);

filterChain.doFilter(servletRequest, servletResponse);
    }

@Override
    public void init(FilterConfig filterConfig) throws ServletException {

}

@Override
    public void destroy() {

}
}

```

参考：
https://wenku.csdn.net/answer/3a2y795u05

# 解决方式二

如果部署到 Nginx ，图片通过 nginx 跨域，在 Nginx 增加响应头

在网站的cofig文件配置如下：
```
location ~ ..(gif|jpg|jpeg|png|bmp|swf)$
{
    add_header Access-Control-Allow-Origin ;
    add_header Access-Control-Allow-Headers X-Requested-With;
    add_header Access-Control-Allow-Methods GET,POST,OPTIONS;

expires      30d;  
    error_log off;  
    access_log /dev/null;  
}
```

参考：
https://ask.dcloud.net.cn/article/38944

原文出处：http://malaoshi.top/show_1IX7BJTgCx9o.html