DAO模式的好處是資料訪問和業務邏輯分離，便於資料維護，業務邏輯不需要了解訪問細節。
DAO的組成：
1.DatabaseConnection：負責開啟和關閉資料庫；
2.VO：包含屬性以及其getter和setter方法；
3.DAO：定義操作的介面，使之更標準；
4.Impl：DAO介面的真實實現類，完成具體的資料庫操作，但不負責資料庫的開啟和關閉；
5.Proxy：代理實現類，完成資料庫的開啟和關閉，呼叫真實實現類物件的操作；
6.Factory：通過Factory獲得DAO的一個例項化物件。

DAO操作標準：

package dao;

import vo.User;

public
 
 interface IUserDAO {
    public boolean findLogin(User user);//登陸時查詢使用者
    public boolean findRegister(String name);//註冊時查詢使用者名稱
    public boolean doCreate(User user);//註冊新使用者
}

DAO真實實現類：

package dao.impl;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import
 
 java.sql.SQLException;

import dao.IUserDAO;
import vo.User;

public class UserDAOImpl implements IUserDAO {
    private Connection conn = null;
    private PreparedStatement ps = null;
    public UserDAOImpl(Connection conn){
        this.conn = conn;
    }
    @Override
    public boolean findLogin
 
(User user) {
        // TODO Auto-generated method stub
        boolean flag = false;
        String sql="SELECT uname FROM user WHERE uname=? AND upassw=?";
        try {
            this.ps = this.conn.prepareStatement(sql);
            this.ps.setString(1, user.getUname());
            this.ps.setString(2, user.getUpassw());
            ResultSet rs = this.ps.executeQuery();
            if(rs.next()){
                flag = true;
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            if(this.ps != null){
                try {
                    this.ps.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
        return flag;
    }
    @Override
    public boolean findRegister(String name) {
        // TODO Auto-generated method stub
        boolean flag = false;
        String sql="SELECT uname FROM user WHERE uname=?";
        try {
            this.ps = this.conn.prepareStatement(sql);
            this.ps.setString(1, name);
            ResultSet rs = this.ps.executeQuery();
            if(rs.next()){
                flag = true;
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            if(this.ps != null){
                try {
                    this.ps.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
        return flag;
    }
    @Override
    public boolean doCreate(User user) {
        // TODO Auto-generated method stub
        boolean flag = false;
        String sql = "INSERT INTO user (uname,upassw,email,mibao) VALUES (?,?,?,?)";
        try {
            this.ps = this.conn.prepareStatement(sql);
            this.ps.setString(1, user.getUname());
            this.ps.setString(2, user.getUpassw());
            this.ps.setString(3, user.getEmail());
            this.ps.setString(4, user.getMibao());
            if(this.ps.executeUpdate() > 0){
                flag = true;
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            if(this.ps != null){
                try {
                    this.ps.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
        return flag;
    }
}

DAO代理實現類：

package dao.proxy;

import java.sql.SQLException;

import dao.IUserDAO;
import dao.impl.UserDAOImpl;
import dbc.DatabaseConnection;
import vo.User;

public class UserDAOProxy implements IUserDAO {
    private DatabaseConnection dbc = null;
    private IUserDAO dao = null;
    public UserDAOProxy(){
        try {
            this.dbc = new DatabaseConnection();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        this.dao = new UserDAOImpl(this.dbc.getConn());
    }
    @Override
    public boolean findLogin(User user) {
        // TODO Auto-generated method stub
        boolean flag = false;
        try{
            flag = this.dao.findLogin(user);
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            this.dbc.close();
        }
        return flag;
    }
    @Override
    public boolean findRegister(String name) {
        // TODO Auto-generated method stub
        boolean flag = false;
        try{
            flag = this.dao.findRegister(name);
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            this.dbc.close();
        }
        return flag;
    }
    @Override
    public boolean doCreate(User user) {
        // TODO Auto-generated method stub
        boolean flag = false;
        try{
            flag = this.dao.doCreate(user);
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            this.dbc.close();
        }
        return flag;
    }
}

DAO工廠類：

package factory;

import dao.IUserDAO;
import dao.proxy.UserDAOProxy;

public class DAOFactory {
    public static IUserDAO getIUserDAOInstance(){
        return new UserDAOProxy();
    }
}