案例

package com.zcc;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
/**
 * @author 23839
 */
@WebFilter(filterName = "HtmlFilter1",urlPatterns = "/*",servletNames = "elHtml")
public class HtmlFilter1 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("HtmlFilter1-------我被初始化了！！！");
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("HtmlFilter1-----我在开始过滤呢！！！");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=utf-8");
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        HttpSession httpSession = request.getSession();
        if (httpSession == null) {
            response.sendRedirect("/el.jsp");
        } else {
            filterChain.doFilter(servletRequest, servletResponse);
            System.out.println("-----------------------------------------");
            System.out.println("HtmlFilter过滤器已放行！");
        }
    }
    @Override
    public void destroy() {
        System.out.println("HtmlFilter1-----我被销毁了！");
    }
}