MVC三层架构

1，MVC三层架构

什么是MVC：Model view Controller 模型 视图 控制器

用户直接访问控制层，控制层就可以直接操作数据库；程序臃肿，不利于维护。

架构：加一层

1.1 MVC三层架构

Model

*业务处理：业务逻辑（service）

*数据持久层：CRUD（Dao）

View

*展示数据

*提供链接发起service请求（a,form,img...）

Controller（servlet）

*接受用户的请求：（req：请求参数，session信息）

*交给业务层处理对应的代码

*控制视图的跳转

2，Filter过滤器

filter：过滤器，用来过滤网站的数据

*处理中文乱码

*登录验证

2.1 filter开发步骤

1.导包

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.fan</groupId>
    <artifactId>javaweb-filter</artifactId>
    <version>1.0-SNAPSHOT</version>
<dependencies>

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>jsp-api</artifactId>
        <version>2.0</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet.jsp.jstl</groupId>
        <artifactId>jstl-api</artifactId>
        <version>1.2</version>
    </dependency>

    <dependency>
        <groupId>taglibs</groupId>
        <artifactId>standard</artifactId>
        <version>1.1.2</version>
    </dependency>
<!--连接数据库-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.32</version>
    </dependency>
</dependencies>

</project>

2，编写过滤器

实现filter接口，重写对应的方法即可。

package com.fan.filter;

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

public class CharacterEncodingFilter implements Filter {
    //初始化，web服务器开始时，就随之初始化。
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化");
    }
    //chain 链
    //1，过滤器中的所有代码，在过滤特定请求的时候都会执行。2，必须要让过滤器继续同行
    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。。。。");
        chain.doFilter(request,response);//让我们的请求继续走，如果不写，程序到这里就被拦截停止了。
        System.out.println("CharacterEncodingFilter执行后。。。。");

    }
    //销毁，web服务器关闭的时候，过滤会销毁。
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁");
    }
}

在web.xml中配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.fan.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/s</url-pattern>
    </filter-mapping>



</web-app>

2.2 监听器

<listener>
    <listener-class>co m.fan.listener</listener-class>
</listener>

package com.fan.util;

public class Constant {
    public static String USER_SESSION="USER_SESSION";
}

package com.fan.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class loginServlet extends HttpServlet {
    @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")){//登录成功
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("/sys/success.jsp");
        }else{//登录失败
            resp.sendRedirect("/error.jsp");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

package com.fan.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class logoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        if (user_session!=null){
            req.getSession().removeAttribute("USER_SESSION");
            resp.sendRedirect("/login.jsp") ;
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    }
}