DAO设计模式
1. DAO简介
DAO的全称是：Data Access Object，数据访问对象。使用DAO设计模式来封装数据库持久层所有操作（CRUD） ，使低级的数据逻辑和高级的业务分离，达到解耦合的目的。
一个典型的DAO实现有如下的组件：
1）一个DAO接口
2）一个实现了DAO的具体实现类
3）一个DAO工厂类
4）数据传输对象（有时称为值对象）
以维护一个客户信息为例，具体的组件如下：
CustomerDao接口
CustomerDaoImpl（接口的具体实现类）
CustomerFactory（工厂类，实例化用）
Customer值对象（VO）
2. DAO实例
2.1 用户登录、注册
功能：用户登录、用户注册、检查用户唯一性。
UserDao.java
package com.amaker.dao;
import com.amaker.bean.User;
public interface UserDao {
// login
public User login(String username, String password);
// register
public void register(User u);
// check
public boolean check(String username);
}
UserDaoImpl.java
package com.amaker.dao.impl;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.amaker.bean.User;
import com.amaker.dao.UserDao;
import com.amaker.util.DBUtil;
public class UserDaoImpl implements UserDao {
@Override
public User login(String username, String password) {
String sql = "select id,username,password from UserTable where username=? and password=?";
DBUtil util = new DBUtil();
Connection conn = util.openConnection();
try {
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setString(1, username);
pstmt.setString(2, password);
ResultSet rs = pstmt.executeQuery();
if (rs.next()) {
int id = rs.getInt(1);
User user = new User();
user.setId(id);
user.setUsername(username);
user.setPassword(password);
return user;
}
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
@Override
public void register(User u) {
String sql = "insert into UserTable (id,username,password) values (?,?,?)";
DBUtil util = new DBUtil();
Connection conn = util.openConnection();
try {
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, u.getId());
pstmt.setString(2, u.getUsername());
pstmt.setString(3, u.getPassword());
pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
util.closeConnection(conn);
}
}
@Override
public boolean check(String username) {
String sql = "select id,username,password from UserTable where username=?";
DBUtil util = new DBUtil();
Connection conn = util.openConnection();
try {
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setString(1, username);
ResultSet rs = pstmt.executeQuery();
if (rs.next()) {
return true;
}
} catch (SQLException e) {
e.printStackTrace();
}
return false;
}
}
User.java
package com.amaker.bean;
public class User {
private int id;
private String username;
private String password;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
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;
}
}
测试类：
package com.amaker.test;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.amaker.bean.User;
import com.amaker.dao.UserDao;
import com.amaker.dao.impl.UserDaoImpl;
public class UserDaoImplTest {
UserDao dao = null;
@Before
public void setUp() throws Exception {
dao = new UserDaoImpl();
}
@After
public void tearDown() throws Exception {
}
@Test
public void testRegister() {
User u = new User();
u.setId(1);
u.setUsername("tom");
u.setPassword("123");
dao.register(u);
}
@Test
public void testCheck() {
boolean b = dao.check("tom");
System.out.println(b);
}
@Test
public void testLogin() {
User u = dao.login("tom", "123");
System.out.println(u.getUsername());
}
}
测试结果：
2.2 订餐系统后台
功能：添加订餐信息、查询订餐信息。
创建MealTypeTbl表：
mysql> create table MealTypeTbl(id int,name varchar(20),price int);
Query OK, 0 rows affected (0.01 sec)
mysql> insert into MealTypeTbl (id,name,price) values (1,"big",10);
Query OK, 1 row affected (0.00 sec)
mysql> insert into MealTypeTbl (id,name,price) values (2,"small",8);
Query OK, 1 row affected (0.00 sec)mysql> select * from MealTypeTbl;
+------+-------+-------+
| id | name | price |
+------+-------+-------+
| 1 | big | 10 |
| 2 | small | 8 |
+------+-------+-------+
2 rows in set (0.00 sec)
创建MealTbl表：
mysql> desc MealTbl;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| createTime | varchar(20) | YES | | NULL | |
| UserID | int(11) | YES | | NULL | |
| MealTypeID | int(11) | YES | | NULL | |
| num | int(11) | YES | | NULL | |
| comment | varchar(20) | YES | | NULL | |
+------------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
mysql> select * from MealTbl;
+------+------------+--------+------------+------+---------+
| id | createTime | UserID | MealTypeID | num | comment |
+------+------------+--------+------------+------+---------+
| 1 | 2016-2-18 | 2 | 1 | 2 | 0k |
+------+------------+--------+------------+------+---------+
1 row in set (0.00 sec)
MealDao.java
package com.amaker.dao;
import java.util.List;
import com.amaker.bean.Meal;
import com.amaker.bean.MealBean;
public interface MealDao {
// add
public void add(Meal meal);
// query
public List list();
}
MealDaoImpl.java
package com.amaker.dao.impl;
import java.sql.Connection;
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 com.amaker.bean.Meal;
import com.amaker.bean.MealBean;
import com.amaker.dao.MealDao;
import com.amaker.util.DBUtil;
public class MealDaoImpl implements MealDao {
@Override
public void add(Meal meal) {
DBUtil util = new DBUtil();
Connection conn = util.openConnection();
String sql = "insert into MealTbl (id,createTime,UserID,MealTypeID,num,comment) values (?,?,?,?,?,?) ";
try {
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, meal.getId());
pstmt.setString(2, meal.getCreateTime());
pstmt.setInt(3, meal.getUserID());
pstmt.setInt(4, meal.getMealType());
pstmt.setInt(5, meal.getNum());
pstmt.setString(6, meal.getComment());
pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
util.closeConnection(conn);
}
}
@Override
public List list() {
DBUtil util = new DBUtil();
Connection conn = util.openConnection();
String sql = "select mt.id, mt.createTime, ut.username, mtt.name, mtt.price, mt.num, mtt.price*mt.num as total, mt.comment from MealTbl as mt left join UserTable as ut on mt.UserID=ut.id left join MealTypeTbl as mtt on mt.MealTypeID=mtt.id";
try {
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sql);
List list = new ArrayList();
while (rs.next()) {
int id = rs.getInt(1);
String createTime = rs.getString(2);
String username = rs.getString(3);
String name = rs.getString(4);
int price = rs.getInt(5);
int num = rs.getInt(6);
int total = rs.getInt(7);
String comment = rs.getString(8);
MealBean mb = new MealBean();
mb.setId(id);
mb.setCreateTime(createTime);
mb.setUsername(username);
mb.setName(name);
mb.setPrice(price);
mb.setNum(num);
mb.setTotal(total);
mb.setComment(comment);
list.add(mb);
}
return list;
} catch (SQLException e) {
e.printStackTrace();
} finally {
util.closeConnection(conn);
}
return null;
}
}
Meal.java
package com.amaker.bean;
public class Meal {
private int id;
private String createTime;
private int userID;
private int mealType;
private int num;
private String comment;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCreateTime() {
return createTime;
}
public void setCreateTime(String createTime) {
this.createTime = createTime;
}
public int getUserID() {
return userID;
}
public void setUserID(int userID) {
this.userID = userID;
}
public int getMealType() {
return mealType;
}
public void setMealType(int mealType) {
this.mealType = mealType;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public String getComment() {
return comment;
}
public void setComment(String comment) {
this.comment = comment;
}
}
MealTpye.java
package com.amaker.bean;
public class MealType {
private int id;
private String name;
private int price;
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 int getPrice() {
return price;
}
public void setPrice(int price) {
this.price = price;
}
}
MealBean.java
package com.amaker.bean;
public class MealBean {
private int id;
private String createTime;
private String username;
private String name;
private int price;
private int num;
private int total;
private String comment;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCreateTime() {
return createTime;
}
public void setCreateTime(String createTime) {
this.createTime = createTime;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getPrice() {
return price;
}
public void setPrice(int price) {
this.price = price;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public int getTotal() {
return total;
}
public void setTotal(int total) {
this.total = total;
}
public String getComment() {
return comment;
}
public void setComment(String comment) {
this.comment = comment;
}
@Override
public String toString() {
return "MealBean [id=" + id + ", createTime=" + createTime
+ ", username=" + username + ", name=" + name + ", price="
+ price + ", num=" + num + ", total=" + total + ", comment="
+ comment + "]";
}
}