过滤器

• Filter：用来过滤网站的数据
  • 登录验证、处理中文乱码等

开发步骤

• 导包，实现javax.servlet.Filter接口

• 重写init、doFilter、destroy三个方法

  • public class CharacterEncodingFilter implements Filter {
        public void init(FilterConfig filterConfig) throws ServletException {
            //服务器启动时初始化
            System.out.println("CharacterEncodingFilter初始化!");
        }
    
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            request.setCharacterEncoding("utf-8");
            response.setCharacterEncoding("utf-8");
            response.setContentType("text/html;charset=UTF-8");
            System.out.println("CharacterEncodingFilter执行前...");
            //让请求继续走，如果不写，程序到这里就被拦截停止了
            chain.doFilter(request, response);
            System.out.println("CharacterEncodingFilter执行后...");
        }
    
        public void destroy() {
            //服务器关闭时销毁
            System.out.println("CharacterEncodingFilter销毁!");
        }
    }
    

• 在web.xml中配置

  • <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.yhr.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <!--过滤/servlet/下的任何请求-->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>
    

登陆验证

• Servlet：

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //获取前端请求的参数
    String username = req.getParameter("username");
    if(username.equals("admin")){
        req.getSession().setAttribute(Constant.USER_SESSION, req.getSession().getId());
        resp.sendRedirect("/sys/success.jsp");
    } else{
        resp.sendRedirect("/error.jsp");
    }
}

• Filter：

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletResponse httpResponse = (HttpServletResponse) response;
    if(httpRequest.getSession().getAttribute(Constant.USER_SESSION) == null){
        httpResponse.sendRedirect("/error.jsp");
    }

    chain.doFilter(request,response);
}

过滤器

原文：https://www.cnblogs.com/xiafrog/p/14344350.html