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MVC架构基础教程

更多内容，点击了解： https://how2j.cn/k/mvc/mvc-tutorials/561.html?p=81777

目录

MVC系列教材 （一）- 教程

MVC系列教材 （二）- 结合Servlet和JSP 实现查询功能

MVC系列教材 （三）- 结合Servlet和JSP 实现分页功能

MVC系列教材 （四）- 使用Servlet 验证用户是否登陆

MVC系列教材 （一）- 教程

MVC是一种分层的设计模式，本章节从Servlet和JSP的局限性谈起，慢慢引入MVC的概念。

 

步骤 1 : 仅仅使用Servlet的短处

在Servlet的章节中，使用了编辑Hero的Servlet
根据浏览器提交的id，通过HeroDAO找到对应的Hero,然后在Servlet中组织html显示出来。

可以看到这个Servlet不仅要准备数据，还要准备html。 尤其是准备html，可读性非常差，维护起来也很麻烦

package servlet;

  

import java.io.IOException;

  

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

  

import bean.Hero;

import dao.HeroDAO;

  

public class HeroEditServlet extends HttpServlet {

  

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

  

        int id = Integer.parseInt(request.getParameter("id"));

  

        Hero hero = new HeroDAO().get(id);

  

        StringBuffer format = new StringBuffer();

        response.setContentType("text/html; charset=UTF-8");

  

        format.append("<!DOCTYPE html>");

  

        format.append("<form action='updateHero' method='post'>");

        format.append("名字 ： <input type='text' name='name' value='%s' > <br>");

        format.append("血量 ： <input type='text' name='hp'  value='%f' > <br>");

        format.append("伤害： <input type='text' name='damage'  value='%d' > <br>");

        format.append("<input type='hidden' name='id' value='%d'>");

        format.append("<input type='submit' value='更新'>");

        format.append("</form>");

  

        String html = String.format(format.toString(), hero.getName(), hero.getHp(), hero.getDamage(), hero.getId());

  

        response.getWriter().write(html);

  

    }

}

步骤 2 : 仅仅使用JSP的短处

因为在Servlet中编写html有这样的短板，所以索性直接在JSP中开发编辑Hero这个功能

这时会发现，虽然编写html方便了，但是写java代码不如在Servlet中那么方便

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*,bean.*,java.sql.*"%>

 

<%

    int id = Integer.parseInt(request.getParameter("id"));

    Hero hero = null;

    try {

        Class.forName("com.mysql.jdbc.Driver");

     

        Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                "root", "admin");

     

        Statement s = c.createStatement();

     

        String sql = "select * from hero where id = " + id;

     

        ResultSet rs = s.executeQuery(sql);

     

        if (rs.next()) {

            hero = new Hero();

            String name = rs.getString(2);

            float hp = rs.getFloat("hp");

            int damage = rs.getInt(4);

            hero.name = name;

            hero.hp = hp;

            hero.damage = damage;

            hero.id = id;

        }

     

        s.close();

     

        c.close();

     

    } catch (ClassNotFoundException e) {

        // TODO Auto-generated catch block

        e.printStackTrace();

    } catch (SQLException e) {

        // TODO Auto-generated catch block

        e.printStackTrace();

    }

     

%>

 

<form action='updateHero' method='post'>

    名字 ： <input type='text' name='name' value='<%=hero.getName()%>'> <br>

    血量 ：<input type='text' name='hp' value='<%=hero.getHp()%>'> <br>

    伤害： <input type='text' name='damage' value='<%=hero.getDamage()%>'> <br>

    <input type='hidden' name='id' value='<%=hero.getId()%>'>

    <input type='submit' value='更新'>

</form>

步骤 3 : 结合Servlet和JSP

既然Servlet和JSP都有各自的优势和短板，那么为什么不结合起来扬长避短呢？
HeroEditServlet：只用来从数据库中查询Hero对象，然后跳转到JSP页面

request.setAttribute("hero", hero);


在request中设置hero

request.getRequestDispatcher("editHero.jsp").forward(request, response);


服务端跳转到editHero.jsp，因为是服务端跳转，都属于同一次请求，所以可以在editHero.jsp通过request取出来

editHero.jsp: 不做查询数据库的事情，直接获取从HeroEditServlet传过来的Hero对象，通过EL表达式把request中的hero显示出来

  • HeroEditServlet.java

  • editHero.jsp

package servlet;

 

import java.io.IOException;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroEditServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        int id = Integer.parseInt(request.getParameter("id"));

        Hero hero = new HeroDAO().get(id);

        request.setAttribute("hero", hero);

        request.getRequestDispatcher("editHero.jsp").forward(request, response);

    }

}

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*,bean.*,java.sql.*"%>

 

<form action='updateHero' method='post'>

    名字 ： <input type='text' name='name' value='${hero.name}'> <br>

    血量 ：<input type='text' name='hp' value='${hero.hp}'> <br>

    伤害： <input type='text' name='damage' value='${hero.damage}'> <br>

    <input type='hidden' name='id' value='${hero.id}'>

    <input type='submit' value='更新'>

</form>

步骤 4 : MVC设计模式

上述例子中结合Serlvet和JSP进行数据的显示，就是一种MVC的思想。

M 代表 模型（Model）
V 代表 视图（View） 
C 代表 控制器（controller) 

模型是什么呢？ 模型就是数据，就是dao,bean

视图是什么呢？ 就是网页, JSP，用来展示模型中的数据

控制器是什么？ 控制器用来把不同的数据，显示在不同的视图上。 在这个例子的，Servlet就是充当控制器的角色，把Hero对象，显示在JSP上。

控制器的作用就是把不同的数据(Model)，显示在不同的视图(View)上。

MVC设计模式

 

MVC系列教材 （二）- 结合Servlet和JSP 实现查询功能

使用MVC的思想，结合Servlet和JSP进行查询操作

步骤1:实体类Hero
步骤2:HeroDAO
步骤3:HeroListServlet
步骤4:web.xml
步骤5:listHero.jsp

步骤 1 : 实体类Hero

package bean;

  

public class Hero {

  

    public int id;

    public String name;

    public float hp;

    public int damage;

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public float getHp() {

        return hp;

    }

    public void setHp(float hp) {

        this.hp = hp;

    }

    public int getDamage() {

        return damage;

    }

    public void setDamage(int damage) {

        this.damage = damage;

    }

      

}

步骤 2 : HeroDAO

使用在前面教程中用到的HeroDAO用于从数据库查询数据

package dao;

   

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.ArrayList;

import java.util.List;

  

import bean.Hero;

   

public class HeroDAO {

   

    public HeroDAO() {

        try {

            Class.forName("com.mysql.jdbc.Driver");

        } catch (ClassNotFoundException e) {

            e.printStackTrace();

        }

    }

   

    public Connection getConnection() throws SQLException {

        return DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8","root",

                "admin");

    }

   

    public int getTotal() {

        int total = 0;

        try (Connection c = getConnection(); Statement s = c.createStatement();) {

   

            String sql = "select count(*) from hero";

   

            ResultSet rs = s.executeQuery(sql);

            while (rs.next()) {

                total = rs.getInt(1);

            }

   

            System.out.println("total:" + total);

   

        } catch (SQLException e) {

   

            e.printStackTrace();

        }

        return total;

    }

   

    public void add(Hero hero) {

   

        String sql = "insert into hero values(null,?,?,?)";

        try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

   

            ps.setString(1, hero.name);

            ps.setFloat(2, hero.hp);

            ps.setInt(3, hero.damage);

   

            ps.execute();

   

            ResultSet rs = ps.getGeneratedKeys();

            if (rs.next()) {

                int id = rs.getInt(1);

                hero.id = id;

            }

        } catch (SQLException e) {

   

            e.printStackTrace();

        }

    }

   

    public void update(Hero hero) {

   

        String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";

        try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

   

            ps.setString(1, hero.name);

            ps.setFloat(2, hero.hp);

            ps.setInt(3, hero.damage);

            ps.setInt(4, hero.id);

   

            ps.execute();

   

        } catch (SQLException e) {

   

            e.printStackTrace();

        }

   

    }

   

    public void delete(int id) {

   

        try (Connection c = getConnection(); Statement s = c.createStatement();) {

   

            String sql = "delete from hero where id = " + id;

   

            s.execute(sql);

   

        } catch (SQLException e) {

   

            e.printStackTrace();

        }

    }

   

    public Hero get(int id) {

        Hero hero = null;

   

        try (Connection c = getConnection(); Statement s = c.createStatement();) {

   

            String sql = "select * from hero where id = " + id;

   

            ResultSet rs = s.executeQuery(sql);

   

            if (rs.next()) {

                hero = new Hero();

                String name = rs.getString(2);

                float hp = rs.getFloat("hp");

                int damage = rs.getInt(4);

                hero.name = name;

                hero.hp = hp;

                hero.damage = damage;

                hero.id = id;

            }

   

        } catch (SQLException e) {

   

            e.printStackTrace();

        }

        return hero;

    }

   

    public List<Hero> list() {

        return list(0, Short.MAX_VALUE);

    }

   

    public List<Hero> list(int start, int count) {

        List<Hero> heros = new ArrayList<Hero>();

   

        String sql = "select * from hero order by id desc limit ?,? ";

   

        try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

   

            ps.setInt(1, start);

            ps.setInt(2, count);

   

            ResultSet rs = ps.executeQuery();

   

            while (rs.next()) {

                Hero hero = new Hero();

                int id = rs.getInt(1);

                String name = rs.getString(2);

                float hp = rs.getFloat("hp");

                int damage = rs.getInt(4);

                hero.id = id;

                hero.name = name;

                hero.hp = hp;

                hero.damage = damage;

                heros.add(hero);

            }

        } catch (SQLException e) {

   

            e.printStackTrace();

        }

        return heros;

    }

   

}

步骤 3 : HeroListServlet

作为控制器的HeroListServlet，其作用就是通过dao获取所有的heros对象，然后放在request中，跳转到listHero.jsp

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

    List<Hero> heros = new HeroDAO().list();

        request.setAttribute("heros", heros);

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}

步骤 4 : web.xml

<web-app>

    <servlet>

        <servlet-name>HeroListServlet</servlet-name>

        <servlet-class>servlet.HeroListServlet</servlet-class>

    </servlet>

 

    <servlet-mapping>

        <servlet-name>HeroListServlet</servlet-name>

        <url-pattern>/listHero</url-pattern>

    </servlet-mapping>

</web-app>

步骤 5 : listHero.jsp

作为视图的listHero.jsp，其作用就是把控制器传过来的数据显示出来

listHero.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*"%>

 

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

 

<table align='center' border='1' cellspacing='0'>

    <tr>

        <td>id</td>

        <td>name</td>

        <td>hp</td>

        <td>damage</td>

        <td>edit</td>

        <td>delete</td>

    </tr>

    <c:forEach items="${heros}" var="hero" varStatus="st">

        <tr>

            <td>${hero.id}</td>

            <td>${hero.name}</td>

            <td>${hero.hp}</td>

            <td>${hero.damage}</td>

            <td><a href="editHero?id=${hero.id}">edit</a></td>

            <td><a href="deleteHero?id=${hero.id}">delete</a></td>

        </tr>

    </c:forEach>

</table>

 

MVC系列教材 （三）- 结合Servlet和JSP 实现分页功能

随着数据中记录的增多，网页上显示的数据会越来越多。 

当多到一定程度的时候，就会影响用户的体验。 

解决办法是通过分页技术，一次只显示数据库中的部分数据，如果要看其他数据，可以通过"下一页" "最后一页" 等翻页操作实现

步骤1:首先准备 DAO
步骤2:只显示5条数据
步骤3:下一页
步骤4:上一页
步骤5:第一页
步骤6:最后一页
步骤7:边界处理
步骤8:套上Bootstrap

步骤 1 : 首先准备 DAO

在DAO中提供方法 

public List<Hero> list(int start, int count)


start表示开始的个数，count表示取多少条
比如 list(0, 5) ， 即表示第一页，每页有5条数据
比如 list(5, 5) ， 即表示第二页，每页有5条数据

package dao;

 

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.ArrayList;

import java.util.List;

 

import bean.Hero;

 

public class HeroDAO {

 

    public int getTotal() {

        int total = 0;

        try {

            Class.forName("com.mysql.jdbc.Driver");

 

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                    "root", "admin");

 

            Statement s = c.createStatement();

 

            String sql = "select count(*) from hero";

 

            ResultSet rs = s.executeQuery(sql);

            while (rs.next()) {

                total = rs.getInt(1);

            }

 

            System.out.println("total:" + total);

 

            s.close();

 

            c.close();

 

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        return total;

    }

 

    public void add(Hero hero) {

 

        try {

            Class.forName("com.mysql.jdbc.Driver");

 

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                    "root", "admin");

 

            String sql = "insert into hero values(null,?,?,?)";

            PreparedStatement ps = c.prepareStatement(sql);

            ps.setString(1, hero.name);

            ps.setFloat(2, hero.hp);

            ps.setInt(3, hero.damage);

 

            ps.execute();

 

            ResultSet rs = ps.getGeneratedKeys();

            if (rs.next()) {

                int id = rs.getInt(1);

                hero.id = id;

            }

 

            ps.close();

 

            c.close();

 

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

 

    public void update(Hero hero) {

        try {

            Class.forName("com.mysql.jdbc.Driver");

 

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                    "root", "admin");

 

            String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";

            PreparedStatement ps = c.prepareStatement(sql);

            ps.setString(1, hero.name);

            ps.setFloat(2, hero.hp);

            ps.setInt(3, hero.damage);

            ps.setInt(4, hero.id);

 

            ps.execute();

 

            ps.close();

 

            c.close();

 

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

 

    }

 

    public void delete(int id) {

        try {

            Class.forName("com.mysql.jdbc.Driver");

 

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                    "root", "admin");

 

            Statement s = c.createStatement();

 

            String sql = "delete from hero where id = " + id;

 

            s.execute(sql);

 

            s.close();

 

            c.close();

 

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

 

    public Hero get(int id) {

        Hero hero = null;

        try {

            Class.forName("com.mysql.jdbc.Driver");

 

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                    "root", "admin");

 

            Statement s = c.createStatement();

 

            String sql = "select * from hero where id = " + id;

 

            ResultSet rs = s.executeQuery(sql);

 

            if (rs.next()) {

                hero = new Hero();

                String name = rs.getString(2);

                float hp = rs.getFloat("hp");

                int damage = rs.getInt(4);

                hero.name = name;

                hero.hp = hp;

                hero.damage = damage;

                hero.id = id;

            }

 

            s.close();

 

            c.close();

 

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        return hero;

    }

 

    public List<Hero> list() {

        return list(0, Short.MAX_VALUE);

    }

 

    public List<Hero> list(int start, int count) {

        List<Hero> heros = new ArrayList<Hero>();

 

        try {

            Class.forName("com.mysql.jdbc.Driver");

 

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",

                    "root", "admin");

 

            String sql = "select * from hero order by id desc limit ?,? ";

 

            PreparedStatement ps = c.prepareStatement(sql);

            ps.setInt(1, start);

            ps.setInt(2, count);

 

            ResultSet rs = ps.executeQuery();

 

            while (rs.next()) {

                Hero hero = new Hero();

                int id = rs.getInt(1);

                String name = rs.getString(2);

                float hp = rs.getFloat("hp");

                int damage = rs.getInt(4);

                hero.id = id;

                hero.name = name;

                hero.hp = hp;

                hero.damage = damage;

                heros.add(hero);

            }

 

            ps.close();

 

            c.close();

 

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        return heros;

    }

 

}

步骤 2 : 只显示5条数据

修改HeroListServlet

int start = 0;

int count = 5;

List<Hero> heros = new HeroDAO().list(start, count);


即表示只获取5条数据

只显示5条数据

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html; charset=UTF-8");

 

        int start = 0;

        int count = 5;

        List<Hero> heros = new HeroDAO().list(start, count);

 

        request.setAttribute("heros", heros);

 

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}

步骤 3 : 下一页

HeroListServlet : 
通过参数获取start，如果浏览器没有传递参数，就设置为0。 
根据start，计算next. next的值就是start+count.
然后把next传递给listHero.jsp

listHero.jsp
在最后面增加一个超链

<a href="?start=${next}">[下一页]</a>


start=${next} 从服务器传递过来的next值

下一页

  • HeroListServlet.java

  • listHero.jsp

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html; charset=UTF-8");

 

        int start = 0;

        int count = 5;

 

        try {

            start = Integer.parseInt(request.getParameter("start"));

        } catch (NumberFormatException e) {

            // 当浏览器没有传参数start时

        }

 

        int next = start + count;

 

        List<Hero> heros = new HeroDAO().list(start, count);

 

        request.setAttribute("next", next);

 

        request.setAttribute("heros", heros);

 

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*"%>

 

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

 

<table align='center' border='1' cellspacing='0'>

    <tr>

        <td>id</td>

        <td>name</td>

        <td>hp</td>

        <td>damage</td>

        <td>edit</td>

        <td>delete</td>

    </tr>

    <c:forEach items="${heros}" var="hero" varStatus="st">

        <tr>

            <td>${hero.id}</td>

            <td>${hero.name}</td>

            <td>${hero.hp}</td>

            <td>${hero.damage}</td>

            <td><a href="editHero?id=${hero.id}">edit</a></td>

            <td><a href="deleteHero?id=${hero.id}">delete</a></td>

        </tr>

    </c:forEach>

    <tr>

        <td colspan="6" align="center">

            <a href="?start=${next}">[下一页]</a>

        </td>

    </tr>

</table>

步骤 4 : 上一页

HeroListServlet:
根据start，计算pre. pre的值就是start-count.
然后把pre传递给listHero.jsp

listHero.jsp
在下一页前增加一个超链

<a href="?start=${pre}">[上一页]</a>


start=${pre} 从服务器传递过来的pre值

上一页

  • HeroListServlet.java

  • listHero.jsp

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html; charset=UTF-8");

 

        int start = 0;

        int count = 5;

 

        try {

            start = Integer.parseInt(request.getParameter("start"));

        } catch (NumberFormatException e) {

            // 当浏览器没有传参数start时

        }

 

        int next = start + count;

        int pre = start - count;

 

        request.setAttribute("next", next);

        request.setAttribute("pre", pre);

 

        List<Hero> heros = new HeroDAO().list(start, count);

        request.setAttribute("heros", heros);

 

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*"%>

 

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

 

<table align='center' border='1' cellspacing='0'>

    <tr>

        <td>id</td>

        <td>name</td>

        <td>hp</td>

        <td>damage</td>

        <td>edit</td>

        <td>delete</td>

    </tr>

    <c:forEach items="${heros}" var="hero" varStatus="st">

        <tr>

            <td>${hero.id}</td>

            <td>${hero.name}</td>

            <td>${hero.hp}</td>

            <td>${hero.damage}</td>

            <td><a href="editHero?id=${hero.id}">edit</a></td>

            <td><a href="deleteHero?id=${hero.id}">delete</a></td>

        </tr>

    </c:forEach>

    <tr>

        <td colspan="6" align="center">

            <a href="?start=${pre}">[上一页]</a>

            <a href="?start=${next}">[下一页]</a>

        </td>

    </tr>

</table>

步骤 5 : 第一页

只需要修改listHero.jsp即可

增加 

<a href="?start=0">[首  页]</a>


因为首页的start永远都是0

第一页

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*"%>

 

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

 

<table align='center' border='1' cellspacing='0'>

    <tr>

        <td>id</td>

        <td>name</td>

        <td>hp</td>

        <td>damage</td>

        <td>edit</td>

        <td>delete</td>

    </tr>

    <c:forEach items="${heros}" var="hero" varStatus="st">

        <tr>

            <td>${hero.id}</td>

            <td>${hero.name}</td>

            <td>${hero.hp}</td>

            <td>${hero.damage}</td>

            <td><a href="editHero?id=${hero.id}">edit</a></td>

            <td><a href="deleteHero?id=${hero.id}">delete</a></td>

        </tr>

    </c:forEach>

    <tr>

        <td colspan="6" align="center">

            <a href="?start=0">[首  页]</a>

            <a href="?start=${pre}">[上一页]</a>

            <a href="?start=${next}">[下一页]</a>

        </td>

    </tr>

</table>

步骤 6 : 最后一页

HeroListServlet:
在HeroListServlet中计算last
last需要根据总数total和每页有多少条数据count来计算得出。

同时，还要看total是否能够整除count
假设总数是50，是能够被5整除的，那么最后一页的开始就是45

if (0 == total % count)

  last = total - count;


假设总数是51，不能够被5整除的，那么最后一页的开始就是50

last = total - total % count;



listHero.jsp
在下一页后增加一个超链

<a href="?start=${last}">[末 页]</a>


start=${last} 从服务器传递过来的last值

最后一页

  • HeroListServlet.java

  • listHero.jsp

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html; charset=UTF-8");

 

        int start = 0;

        int count = 5;

 

        try {

            start = Integer.parseInt(request.getParameter("start"));

        } catch (NumberFormatException e) {

            // 当浏览器没有传参数start时

        }

 

        int next = start + count;

        int pre = start - count;

 

        int total = new HeroDAO().getTotal();

 

        int last;

        // 假设总数是50，是能够被5整除的，那么最后一页的开始就是45

        if (0 == total % count)

            last = total - count;

        // 假设总数是51，不能够被5整除的，那么最后一页的开始就是50

        else

            last = total - total % count;

 

        request.setAttribute("next", next);

        request.setAttribute("pre", pre);

        request.setAttribute("last", last);

 

        List<Hero> heros = new HeroDAO().list(start, count);

        request.setAttribute("heros", heros);

 

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*"%>

 

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

 

<table align='center' border='1' cellspacing='0'>

    <tr>

        <td>id</td>

        <td>name</td>

        <td>hp</td>

        <td>damage</td>

        <td>edit</td>

        <td>delete</td>

    </tr>

    <c:forEach items="${heros}" var="hero" varStatus="st">

        <tr>

            <td>${hero.id}</td>

            <td>${hero.name}</td>

            <td>${hero.hp}</td>

            <td>${hero.damage}</td>

            <td><a href="editHero?id=${hero.id}">edit</a></td>

            <td><a href="deleteHero?id=${hero.id}">delete</a></td>

        </tr>

    </c:forEach>

    <tr>

        <td colspan="6" align="center">

            <a href="?start=0">[首  页]</a>

            <a href="?start=${pre}">[上一页]</a>

            <a href="?start=${next}">[下一页]</a>

            <a href="?start=${last}">[末  页]</a>

        </td>

    </tr>

</table>

步骤 7 : 边界处理

上一页，下一页有一个问题，
如果在第一页点击上一页，就会看不到数据了，因为在第一页的时候，pre=-5,也就导致传递到serlvet的start=-5;
同样的在最后一页的时候，点击下一页，也有类似的问题。

解决办法是进行边界处理：

pre = pre < 0 ? 0 : pre;


如果pre是负数了，就使用0 

next = next > last ? last : next;


如果next大于last，就使用last

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        response.setContentType("text/html; charset=UTF-8");

 

        int start = 0;

        int count = 5;

 

        try {

            start = Integer.parseInt(request.getParameter("start"));

        } catch (NumberFormatException e) {

            // 当浏览器没有传参数start时

        }

 

        int next = start + count;

        int pre = start - count;

 

        int total = new HeroDAO().getTotal();

 

        int last;

        if (0 == total % count)

            last = total - count;

        else

            last = total - total % count;

 

        pre = pre < 0 ? 0 : pre;

        next = next > last ? last : next;

 

        request.setAttribute("next", next);

        request.setAttribute("pre", pre);

        request.setAttribute("last", last);

 

        List<Hero> heros = new HeroDAO().list(start, count);

        request.setAttribute("heros", heros);

 

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}

步骤 8 : 套上Bootstrap

套上Bootstrap

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*"%>

<!DOCTYPE html>

<script src="https://how2j.cn/study/js/jquery/2.0.0/jquery.min.js"></script>

<link href="https://how2j.cn/study/css/bootstrap/3.3.6/bootstrap.min.css" rel="stylesheet">

<script src="https://how2j.cn/study/js/bootstrap/3.3.6/bootstrap.min.js"></script>

     

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

 

<script>

$(function(){

    $("a").addClass("btn btn-default btn-xs");

     

});

 

</script>

<table style="width:500px; margin:44px auto" class="table table-striped table-bordered table-hover  table-condensed" align='center' border='1' cellspacing='0'>

    <tr>

        <td>id</td>

        <td>name</td>

        <td>hp</td>

        <td>damage</td>

        <td>edit</td>

        <td>delete</td>

    </tr>

    <c:forEach items="${heros}" var="hero" varStatus="st">

        <tr>

            <td>${hero.id}</td>

            <td>${hero.name}</td>

            <td>${hero.hp}</td>

            <td>${hero.damage}</td>

            <td><a href="editHero?id=${hero.id}">编辑</a></td>

            <td><a href="deleteHero?id=${hero.id}">删除</a></td>

        </tr>

    </c:forEach>

 

</table>

        <nav>

          <ul class="pager">

 

            <li><a href="?start=0">首  页</a></li>

            <li><a href="?start=${pre}">上一页</a></li>

            <li><a href="?start=${next}">下一页</a></li>

            <li><a href="?start=${last}">末  页</a></li>

          </ul>           

        </nav>

 

MVC系列教材 （四）- 使用Servlet 验证用户是否登陆

比如网站提供Hero查询服务，但是前提是用户要登录过才能使用。 

如果用户登陆过了，访问listHero，就让用户正常访问，否则就跳转到登陆界面。 

这是非常常见的场景，通过使用 session 来实现这个功能。 

在处理登录的loginServlet 中使用将用户名保存在session中。 

在HeroListServlet 中查看session中是否为空。如果为空，就表示用户没有登陆过，就跳转到登陆页面

步骤1:在LoginServlet 把验证成功的用户加入到 Session
步骤2:在HeroListServlet判断Session中是否有数据

步骤 1 : 在LoginServlet 把验证成功的用户加入到 Session

如果用户输入正确的账号密码，就跳转到 listHero，并且把用户名以"userName"放进session

如果用户输入错误的账号密码，就跳转到 login.html，让用户重新登陆

import java.io.IOException;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

public class LoginServlet extends HttpServlet {

 

    private static final long serialVersionUID = 1L;

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        String name = request.getParameter("name");

        String password = request.getParameter("password");

 

        if ("admin".equals(name) && "123".equals(password)) {

            request.getSession().setAttribute("userName", name);

            response.sendRedirect("listHero");

        } else {

            response.sendRedirect("login.html");

        }

 

    }

}

步骤 2 : 在HeroListServlet判断Session中是否有数据

String userName = (String) request.getSession().getAttribute("userName");

   if (null == userName) {

   response.sendRedirect("login.html");

   return;

}



从session中取出userName，如果是空，就表示用户没有登录，或者登录已经超过了30分钟。 客户端跳转到login.html，让用户重新登陆

package servlet;

 

import java.io.IOException;

import java.util.List;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import bean.Hero;

import dao.HeroDAO;

 

public class HeroListServlet extends HttpServlet {

 

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

 

        String userName = (String) request.getSession().getAttribute("userName");

        if (null == userName) {

            response.sendRedirect("login.html");

            return;

        }

 

        int start = 0;

        int count = 5;

 

        try {

            start = Integer.parseInt(request.getParameter("start"));

        } catch (NumberFormatException e) {

            // 当浏览器没有传参数start时

        }

 

        int next = start + count;

        int pre = start - count;

 

        int total = new HeroDAO().getTotal();

 

        int last;

        if (0 == total % count)

            last = total - count;

        else

            last = total - total % count;

 

        pre = pre < 0 ? 0 : pre;

        next = next > last ? last : next;

 

        request.setAttribute("next", next);

        request.setAttribute("pre", pre);

        request.setAttribute("last", last);

 

        List<Hero> heros = new HeroDAO().list(start, count);

        request.setAttribute("heros", heros);

 

        request.getRequestDispatcher("listHero.jsp").forward(request, response);

 

    }

}


更多内容，点击了解： https://how2j.cn/k/mvc/mvc-tutorials/561.html?p=81777


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