一，DAO设计模式用于 j2ee 的数据层访问，包括五部分，

数据库连接类（包含数据库的连接与关闭操作的一个类），

VO类（私有变量与数据库表格对应，接收数据库中表格各字段内容），

DAO接口类（包含数据库的各项操作，增，删，改，查函数的定义），

DAO实现类（具体实现DAO接口中定义的数据库操作函数），

DAO工厂类（提供一个返回值为DAO接口类型的静态方法，获得DAO实现的实例）

以一个mysql数据库中简单的用户表（userid 自增长,username,password）为例的DAO各个模块：

　　1.数据库连接类：

package com.javaweb.dao;

import java.sql.*;

public class DBConnection

{

    private final String DBDRIVER = "com.mysql.jdbc.Driver";

    private final String DBURL = "jdbc:mysql://localhost:3306/javaweb";

    private final String USER = "root";

    private final String PASSWORD = "root";

    private Connection conn=null;

    public DBConnection()

    {

        try

        {

            Class.forName(DBDRIVER);

            this.conn = DriverManager.getConnection(DBURL,USER,PASSWORD);

        } catch (ClassNotFoundException | SQLException e)

        {

            // TODO Auto-generated catch block

            System.out.println("加载驱动失败");

        }

    }

    public Connection getConnection()

    {

        return this.conn;

    }

    public void close()

    {

        if(this.conn!=null)

        {

            try

            {

                this.conn.close();

            } catch (SQLException e)

            {

                // TODO Auto-generated catch block

                System.out.println("数据库连接关闭失败");

            }

        }

    }

}

　　2.VO类：

package com.javaweb.dao;

public class User

{

    private int userid;

    private String username;

    private String password;

    public User()

    {

        // TODO Auto-generated constructor stub

    }

    public int getUserid()

    {

        return userid;

    }

    public void setUserid(int userid)

    {

        this.userid = userid;

    }

    public String getUsername()

    {

        return username;

    }

    public void setUsername(String username)

    {

        this.username = username;

    }

    public String getPassword()

    {

        return password;

    }

    public void setPassword(String password)

    {

        this.password = password;

    }

}

　　3.DAO接口：

package com.javaweb.dao;

import java.util.List;

public interface UserDAO

{

    public void insert(User user) throws Exception;

    public void delete(int userid) throws Exception;

    public void update(User user) throws Exception;

    public User querryById(int userid) throws Exception;

    public List querryALL() throws Exception;

}

　　4.DAO具体实现：

package com.javaweb.dao;

import java.util.ArrayList;

import java.util.List;

import java.sql.*;

public class UserDAOImpl implements UserDAO

{

    @Override

    public void insert(User user) throws Exception

    {

        // TODO Auto-generated method stub

        DBConnection con = null;

        PreparedStatement pstm = null;

        String sql = "insert into user(username,password) values(?,?)";

        try

        {

            con = new DBConnection();

            pstm = con.getConnection().prepareStatement(sql);

            pstm.setString(1, user.getUsername());

            pstm.setString(2, user.getPassword());

            pstm.executeUpdate();

            if (pstm != null)

            {

                pstm.close();

            }

        } catch (Exception e)

        {

            // TODO Auto-generated catch block

            System.out.println("插入数据操作异常");

        } finally

        {

            if (con != null)

            {

                con.close();

            }

        }

    }

    @Override

    public void delete(int userid) throws Exception

    {

        // TODO Auto-generated method stub

        DBConnection con = null;

        PreparedStatement pstm = null;

        String sql = "delete from user where userid=?";

        try

        {

            con = new DBConnection();

            pstm = con.getConnection().prepareStatement(sql);

            pstm.setInt(1, userid);

            pstm.executeUpdate();

            if (pstm != null)

            {

                pstm.close();

            }

        } catch (Exception e)

        {

            // TODO Auto-generated catch block

            System.out.println("删除数据操作异常");

        } finally

        {

            if (con != null)

            {

                con.close();

            }

        }

    }

    @Override

    public void update(User user) throws Exception

    {

        // TODO Auto-generated method stub

        // TODO Auto-generated method stub

        DBConnection con = null;

        PreparedStatement pstm = null;

        String sql = "update user set username=?,password=? where userid=?";

        try

        {

            con = new DBConnection();

            pstm = con.getConnection().prepareStatement(sql);

            pstm.setString(1, user.getUsername());

            pstm.setString(2, user.getPassword());

            pstm.setInt(3, user.getUserid());

            pstm.executeUpdate();

            if (pstm != null)

            {

                pstm.close();

            }

        } catch (Exception e)

        {

            // TODO Auto-generated catch block

            System.out.println("更新数据操作异常,sql:"+sql);

        } finally

        {

            if (con != null)

            {

                con.close();

            }

        }

    }

    @Override

    public User querryById(int userid) throws Exception

    {

        // TODO Auto-generated method stub

        DBConnection con = null;

        PreparedStatement pstm = null;

        ResultSet rs=null;

        User user=null;

        String sql = "select * from user where userid=?";

        try

        {

            //获取连接

            con = new DBConnection();

            //预处理语句

            pstm = con.getConnection().prepareStatement(sql);

            //设置参数

            pstm.setInt(1, userid);

            //执行查询

            rs = pstm.executeQuery();

            //获取结果

            while(rs.next())

            {

                user = new User();

                user.setUserid(rs.getInt(1));

                user.setUsername(rs.getString(2));

                user.setPassword(rs.getString(3));

            }

            if (pstm != null)

            {

                pstm.close();

            }

        } catch (Exception e)

        {

            // TODO Auto-generated catch block

            System.out.println("查询数据操作异常   sql:"+sql);

        } finally

        {

            if (con != null)

            {

                con.close();

            }

        }

        return user;

    }

    @Override

    public List<User> querryALL() throws Exception

    {

        // TODO Auto-generated method stub

        DBConnection con = null;

        PreparedStatement pstm = null;

        ResultSet rs=null;

        List<User> lsu=new ArrayList<User>();

        String sql = "select * from user";

        try

        {

            //获取连接

            con = new DBConnection();

            //预处理语句

            pstm = con.getConnection().prepareStatement(sql);

            //执行查询,返回结果rs

            rs = pstm.executeQuery();

            //获取结果

            while(rs.next())

            {

                User user = new User();

                user.setUserid(rs.getInt(1));

                user.setUsername(rs.getString(2));

                user.setPassword(rs.getString(3));

                lsu.add(user);

            }

            if (pstm != null)

            {

                pstm.close();

            }

        } catch (Exception e)

        {

            // TODO Auto-generated catch block

            System.out.println("查询数据操作异常");

        } finally

        {

            if (con != null)

            {

                con.close();

            }

        }

        return lsu;

    }

}

　　5.DAO工厂（有效避免由于DAO实现改变导致的大量代码修改）

package com.javaweb.dao;

public class DAOFactory

{

    public static UserDAO getUserDAOInstance()

    {

        return new UserDAOImpl();

    }

}

二，通过jsp调用相关函数即可进行数据库操作，省去了大量重复代码。

　　代码示例：

<%@page import="com.javaweb.dao.*"%>

<%@page import="org.eclipse.jdt.internal.compiler.apt.model.Factory"%>

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

    pageEncoding="utf-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

<title>Insert title here</title>

</head>

<body>

    <%

        UserDAO userDAO = DAOFactory.getUserDAOInstance();

        User user=new User();

        user.setUsername("lu");

        user.setPassword("123");

        userDAO.insert(user);

    %>

</body>

</html>

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