DAO模式

DAO模式简介：

DataAccessObject,数据存取对象，指位于业务逻辑和持久化数据之间实现对持久化数据的访问，通俗来讲，就是将数据库操作都封装起来，对外提供相应的接口

优点：

1、隔离了数据访问代码和业务代码，业务逻辑代码直接调用DAO方法即可，分工明确，数据访问层代码不影响业务逻辑代码，符合单一职能原则，降低耦合性，提高可复用性

2、隔离了不同数据库实现。采用面向接口编程，如果底层数据库变化，只需增加DAO接口的实现类即可，原有实现类不用修改，符合“”开-闭“”原则降低了耦合性，提高了代码可扩       展性和系统的可移植性。

组成部分：

DAO接口：把对数据库所有的操作定义为抽象方法，可以提供多种实现。

import java.util.List;/** * DAO接口：宠物 * @author 30869 * */public interface IPetDao {/** * 保存宠物 * @param pet 宠物 * @return */int sava(Pet pet);/** * 删除宠物 * @param pet 宠物 * @return */int del(Pet pet);/** * 更新宠物 * @param pet 宠物 * @return */int update(Pet pet);/** * 获得指定昵称的宠物，精确查询 * @param name 昵称 * @return 宠物 */Pet getByName(String name);/** * 获得指定id的Pet * @param id  编号 * @return 宠物对象 */Pet getById(Integer id);/** * 获得指定昵称的宠物列表，模糊查询 * @param name 昵称 * @return 宠物列表 */List<Pet> findByName(String name);/** * 获得指定类型的宠物列表，模糊查询 * @param type 宠物类型 * @return 宠物列表 */List<Pet> findByType(String type);/** * 查询全部的Pet * @return */List<Pet> getAllPet();}

DAO实现类：根据不同数据库给出DAO接口定义方法的具体实现

import java.util.List;/** * PetDAO基于MySql的实现类 *  * @author 30869 *  */public class PetDaoMysqlImpl extends BaseDao implements IPetDao {@Overridepublic int sava(Pet pet) {String preparedSql = "insert into `dog`(`name`,`typeId`) values(?,?)";Object[] param = { pet.getName(), pet.getTypeId() };return executeUpdate(preparedSql, param);}@Overridepublic int del(Pet pet) {String preparedSql = "delete from `dog` where id=?";Object[] param = { pet.getTypeId() };return executeUpdate(preparedSql, param);}@Overridepublic int update(Pet pet) {String preparedSql = "update `dog` set `masterId`=?,`name`=?,`typeId`=?,`health`=?"+ ",`love`=?,`adoptTime`=?,`status`=? where `id`=?";Object[] param = { pet.getMasterId(), pet.getName(), pet.getTypeId(),pet.getHealth(), pet.getLove(), pet.getAdoptTime(),pet.getStatus(), pet.getId() };return executeUpdate(preparedSql, param);}@Overridepublic Pet getById(Integer id) {String preparedSql = "select * from `dog` where `id`=?";Object[] param = { id };rs = executeQuery(preparedSql, param);return getOnePetOfResultSet(rs);}@Overridepublic Pet getByName(String name) {String preparedSql = "select * from `dog` where `name`=?";Object[] param = { name };rs = executeQuery(preparedSql, param);return getOnePetOfResultSet(rs);}@Overridepublic List<Pet> findByName(String name) {String preparedSql = "select * from `dog` where `name` like ?";Object[] param = { "%"+name+"%" };rs = executeQuery(preparedSql, param);return getPetOfResultSet(rs);}@Overridepublic List<Pet> findByType(String type) {String preparedSql = "select * from `dog` where `typeId`=(select `typeId` from `petType` where `petType`=?)";Object[] param = { "%"+type+"%" };rs = executeQuery(preparedSql, param);return getPetOfResultSet(rs);}@Overridepublic List<Pet> getAllPet(){String preparedSql = "select * from `dog`";Object[] param =null; rs=executeQuery(preparedSql, param);return getPetOfResultSet(rs);}}

实体类：用于存放和传输对象数据

import java.io.Serializable;/** * 宠物类，属性和数据库中Pet表的字段一一对应 *  * @author 30869 * */public class Pet implements Serializable{private static final long serialVersionUID = -6079513472113573519L;private Integer id;//宠物IDprivate Integer masterId;//主人IDprivate String name;//昵称private Integer typeId;//类型IDprivate Integer health;//健康值private Integer love;//亲密度private java.sql.Timestamp adoptTime;//领养时间private String status;//状态（未领养和已领养）public Pet() {super();}public Pet(String name, Integer typeId) {super();this.name = name;this.typeId = typeId;}public Pet(Integer id, Integer masterId, String name, Integer typeId,Integer health, Integer love, java.sql.Timestamp adoptTime, String status) {super();this.id = id;this.masterId = masterId;this.name = name;this.typeId = typeId;this.health = health;this.love = love;this.adoptTime = adoptTime;this.status = status;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;

数据连接和关闭工具类：避免数据库连接和关闭代码的重复使用，方便修改

import java.io.IOException;import java.io.InputStream;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 java.util.Properties;/** * 封装了JDBC的连接、关闭等功能 *  * @author 30869 *  */public class BaseDao {protected Connection con = null;// 三个引用为了方便其他类访问(继承类直接用)protected PreparedStatement pstmt = null;protected ResultSet rs = null;private static String driver = "";private static String url = "";private static String user = "";private static String password = "";static{init();}/** * 初始化连接参数 */public static void init() {Properties properties = new Properties();//资源配置文件对象String configFile = "jdbc.properties";//资源配置文件路径InputStream is = BaseDao.class.getClassLoader().getResourceAsStream(configFile);//资源配置文件输入流try {properties.load(is);//从输入流中读取属性列表到资源配置文件对象} catch (IOException e) {e.printStackTrace();}driver = properties.getProperty("driver");//获取资源配置文件valueurl = properties.getProperty("url");user = properties.getProperty("user");password = properties.getProperty("password");}/** * 获取连接 *  * @return */public Connection getConnection() {Connection connection = null;try {Class.forName(driver);connection = DriverManager.getConnection(url, user, password);} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}return connection;}/** * 释放和关闭资源 *  * @param con *            连接对象 * @param pstmt *            语句对象 * @param rs *            结果集对象 */public void clossAll(Connection con, Statement pstmt, ResultSet rs) {if (rs != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (pstmt != null) {try {pstmt.close();} catch (SQLException e) {e.printStackTrace();}}if (con != null) {try {con.close();} catch (SQLException e) {e.printStackTrace();}}}/** * 增、删、改操作 *  * @param preparedSql *            预编译的sql语句 * @param param *            参数数组 * @return 受影响的行数 */public int executeUpdate(String preparedSql, Object[] param) {Connection con = getConnection();int n = 0;try {pstmt = con.prepareStatement(preparedSql);if (param != null) {for (int i = 0; i < param.length; i++) {pstmt.setObject((i + 1), param[i]);}}n = pstmt.executeUpdate();} catch (SQLException e) {e.printStackTrace();} finally {clossAll(con, pstmt, null);}return n;}/** * 查询的通用方法 *  * @param preparedSql *            预编译的sql语句 * @param param *            参数数组 * @return 结果集 */public ResultSet executeQuery(String preparedSql, Object[] param) {Connection con = getConnection();try {pstmt = con.prepareStatement(preparedSql);if (param != null) {for (int i = 0; i < param.length; i++) {pstmt.setObject((i + 1), param[i]);}}rs = pstmt.executeQuery();} catch (SQLException e) {e.printStackTrace();}// 无需关闭，返回值需要被处理return rs;}/** * 从结果集中提取并返回查询结果为1的Pet *  * @param rs * @return */public Pet getOnePetOfResultSet(ResultSet rs) {Pet pet = null;try {if (rs.next()) {pet = new Pet(rs.getInt(1), rs.getInt(2), rs.getString(3),rs.getInt(4), rs.getInt(5), rs.getInt(6),rs.getTimestamp(7), rs.getString(8));}} catch (SQLException e) {e.printStackTrace();} finally {clossAll(con, pstmt, rs);}return pet;}/** * 从结果集中取出Pet对象集合 *  * @param rs * @return */public List<Pet> getPetOfResultSet(ResultSet rs) {Pet pet = null;List<Pet> pets = new ArrayList<>();try {while (rs.next()) {pet = new Pet(rs.getInt(1), rs.getInt(2), rs.getString(3),rs.getInt(4), rs.getInt(5), rs.getInt(6),rs.getTimestamp(7), rs.getString(8));pets.add(pet);}} catch (SQLException e) {e.printStackTrace();} finally {clossAll(con, pstmt, rs);}return pets;}/** * 从结果集中取出1个Master对象 *  * @param rs * @return */public Master getOneMasterOfResultSet(ResultSet rs) {Master master = null;try {if (rs.next()) {master = new Master(rs.getInt(1), rs.getString(2),rs.getString(3), rs.getInt(4));}} catch (SQLException e) {e.printStackTrace();} finally {clossAll(con, pstmt, rs);}return master;}/** * 从结果集中取出Master对象集合 *  * @param rs * @return */public List<Master> getMasterOfResultSet(ResultSet rs) {Master master = null;List<Master> masters = new ArrayList<>();try {while (rs.next()) {master = new Master(rs.getInt(1), rs.getString(2),rs.getString(3), rs.getInt(4));masters.add(master);}} catch (SQLException e) {e.printStackTrace();} finally {clossAll(con, pstmt, rs);}return masters;}/** * 输出Pet集合信息 *  * @param pets */public void showPet(List<Pet> pets) {for (Pet pet : pets) {System.out.println(pet.getId() + "\t" + pet.getMasterId() + "\t"+ pet.getName() + "\t" + pet.getTypeId() + "\t"+ pet.getHealth() + "\t" + pet.getLove() + "\t"+ pet.getAdoptTime() + "\t" + pet.getStatus() + "\t");}}}