MVC三层架构

• Model 模型
• 业务处理：业务逻辑（Service）
• 数据持久层：CRUD(Dao)
• View 视图
• 展示数据
• 提供链接发起Servl请求
• Controller 控制器
• 接收用户的请求
• 交给业务层处理对应的代码
• 控制视图的转跳

Servlet专注于处理请求和控制视图跳转，JSP专注于显示数据

过滤器（重点）

用来过滤网站的数据

开发流程

• 导包
• 编写过滤器编写
• 修改web.xml

编码错误

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().write("你好呀，世界");
    }

添加过滤器

<filter>
    <filter-name>filter1</filter-name>
    <filter-class>top.huii.filter.Filter1</filter-class>
</filter>
<filter-mapping>
    <filter-name>filter1</filter-name>
    <url-pattern>/fi/*</url-pattern>
</filter-mapping>

package top.huii.filter;

import javax.servlet.*;
import java.io.IOException;

public class Filter1 implements Filter {
//    初始化
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        System.out.println("执行前");
        filterChain.doFilter(servletRequest, servletResponse);  //让请求继续走，交给下一个过滤器
        System.out.println("执行后");
    }

//    销毁
    @Override
    public void destroy() {

    }
}

可用作权限拦截等功能。

监听器

实现监听器的接口

web.xml配置

<listener>
    <listener-class>top.huii.listener.Listener</listener-class>
</listener>

package top.huii.listener;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class Listener implements HttpSessionListener {
    @Override
//    一旦创建session，就触发
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        HttpSession session = httpSessionEvent.getSession();
        Integer count = (Integer) session.getAttribute("count");
        if (count == null){
            count = new Integer(0);
        } else {
            int c = count.intValue();
            count = new Integer(c + 1);
        }
        System.out.println(count);
        session.setAttribute("count", count);
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {

    }
}