java中的过滤器：Filter

1. 创建： 实现Filter接口

   /**
    * @author yinfeng
    * @description 跨域解决
    * @since 2021/10/1 17:53
    */
   public class CrossFilter implements Filter {
   
       @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, HEAD");
           response.setHeader("Access-Control-Max-Age", "3600");
           response.setHeader("Access-Control-Allow-Headers", "access-control-allow-origin," +
                   " authority, content-type, version-info, X-Requested-With,token");
           response.setHeader("Content-Type", "application/json; charset=utf-8");
           response.setCharacterEncoding("utf-8");
           filterChain.doFilter(request, response);
       }
   
   }
   
   

2. 生命周期：

   1. 构建Filter对象
   2. 初始化：初始化init方法调用
   3. 开始过滤：doFilter
   4. 销毁：销毁方法destroy方法调用