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>