JavaBean中DAO设计方式介绍

JavaBean中DAO设计模式介绍

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一、信息系统的开发架构

客户层-------显示层-------业务层---------数据层---------数据库

1.客户层：客户层就是客户端，简单的来说就是浏览器。

2.显示层：JSP/Servlet，用于给浏览器显示。

3.业务层：对于数据层的原子操作进行整合。

4.数据层：对于数据库进行的原子操作，增加、删除等；

二、DAO(Data Access Object)介绍

DAO应用在数据层那块,用于访问数据库，对数据库进行操作的类。

三、DAO设计模式的结构

DAO设计模式一般分为几个类：

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1.VO(Value Object)：一个用于存放网页的一行数据即一条记录的类，比如网页要显示一个用户的信息，则这个类就是用户的类。

2.DatabaseConnection：用于打开和关闭数据库。

3.DAO接口：用于声明对于数据库的操作。

4.DAOImpl：必须实现DAO接口，真实实现DAO接口的函数，但是不包括数据库的打开和关闭。

5.DAOProxy：也是实现DAO接口，但是只需要借助DAOImpl即可，但是包括数据库的打开和关闭。

6.DAOFactory：工厂类，含有getInstance()创建一个Proxy类。??

四、DAO的好处

DAO的好处就是提供给用户的接口只有DAO的接口，所以如果用户想添加数据，只需要调用create函数即可，不需要数据库的操作。

五、DAO包命名

对于DAO，包的命名和类的命名一定要有层次。

六、实例解析

1.Emp.java

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1. package?org.vo;??import?java.util.*;??
2. public?class?Emp{??????private?int?empno;??
3. ????private?String?ename;??????private?String?job;??
4. ????private?Date?hireDate;??????private?float?sal;??
5. ????public?Emp(){????????????
6. ????}??????public?int?getEmpno(){??
7. ????????return?empno;??????}??
8. ????public?void?setEmpno(int?empno){??????????this.empno?=?empno;??
9. ????}??????public?String?getEname(){??
10. ????????return?ename;??????}??
11. ????public?void?setEname(String?ename){??????????this.ename?=?ename;??
12. ????}??????public?Date?getHireDate(){??
13. ????????return?hireDate;??????}??
14. ????public?void?setHireDate(Date?hireDate){??????????this.hireDate?=?hireDate;??
15. ????}??????public?float?getSal(){??
16. ????????return?sal;??????}??
17. ????public?void?setSal(float?sal){??????????this.sal?=?sal;??
18. ????}??????public?String?getJob(){??
19. ????????return?job;??????}??
20. ????public?void?setJob(String?job){??????????this.job?=?job;??
21. ????}??}??

2.DatabaseConnection.java

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1. package?org.dbc;??import?java.sql.*;??
2. public?class?DatabaseConnection{??????private?Connection?con?=?null;??
3. ????private?static?final?String?DRIVER?=?"com.mysql.jdbc.Driver";??????private?static?final?String?USER?=?"root";??
4. ????private?static?final?String?URL?=?"jdbc:mysql://localhost:3306/mldn";??????private?static?final?String?PASS?=?"12345";??
5. ????public?DatabaseConnection()throws?Exception{??????????Class.forName(DRIVER);??
6. ????????con?=?DriverManager.getConnection(URL,USER,PASS);??????}??
7. ????public?Connection?getConnection()throws?Exception{??????????return?con;??
8. ????}??????public?void?close()throws?Exception{??
9. ????????if(con!=null){??????????????con.close();??
10. ????????}??????}??
11. }??

3.IEmpDAO.java

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1. package?org.dao;??import?java.util.List;??
2. import?org.vo.*;??public?interface?IEmpDAO{??
3. ????public?boolean?doCreate(Emp?emp)throws?Exception;??????public?List<Emp>?findAll()throws?Exception;??
4. ????public?Emp?findById(int?empno)throws?Exception;??}??

4.EmpDAOImpl.java

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1. package?org.dao.impl;??import?org.dao.*;??
2. import?java.sql.*;??import?org.vo.*;??
3. import?java.util.*;??public?class?EmpDAOImpl?implements?IEmpDAO{??
4. ????private?Connection?con;??????private?PreparedStatement?stat?=?null;??
5. ????public?EmpDAOImpl(Connection?con){??????????this.con?=?con;??
6. ????}??????public?boolean?doCreate(Emp?emp)throws?Exception{??
7. ????????String?sql?=?"INSERT?INTO?emp(empno,ename,job,hiredate,sal)?VALUES(?,?,?,?,?)";??????????stat?=?con.prepareStatement(sql);??
8. ????????stat.setInt(1,emp.getEmpno());??????????stat.setString(2,emp.getEname());??
9. ????????stat.setString(3,emp.getJob());??????????stat.setDate(4,new?java.sql.Date(emp.getHireDate().getTime()));??
10. ????????stat.setFloat(5,emp.getSal());??????????int?update?=?stat.executeUpdate();??
11. ????????if(update>0){??????????????return?true;??
12. ????????}??????????else{??
13. ????????????return?false;??????????}??
14. ????}??????public?List<Emp>?findAll()throws?Exception{??
15. ????????String?sql?=?"SELECT?empno,ename,job,hiredate,sal?FROM?emp";??????????stat?=?con.prepareStatement(sql);??
16. ????????ResultSet?rs?=?stat.executeQuery();??????????Emp?emp?=?null;??
17. ????????List<Emp>?list?=?new?ArrayList<Emp>();??????????while(rs.next()){??
18. ????????????int?empno?=?rs.getInt(1);??????????????String?ename?=?rs.getString(2);??
19. ????????????String?job?=?rs.getString(3);??????????????float?sal?=?rs.getFloat(5);??
20. ????????????emp?=?new?Emp();??????????????emp.setEmpno(empno);??
21. ????????????emp.setEname(ename);??????????????emp.setJob(job);??
22. ????????????emp.setHireDate(rs.getDate(4));??????????????emp.setSal(sal);??
23. ????????????list.add(emp);??????????}??
24. ????????return?list;??????}??
25. ????public?Emp?findById(int?empno)throws?Exception{??????????String?sql?=?"SELECT?empno,ename,job,hiredate,sal?FROM?emp?WHERE?empno=?";??
26. ????????stat?=?con.prepareStatement(sql);??????????stat.setInt(1,empno);??
27. ????????ResultSet?rs?=?stat.executeQuery();??????????Emp?emp?=?null;??
28. ????????if(rs.next()){??????????????String?ename?=?rs.getString(2);??
29. ????????????String?job?=?rs.getString(3);??????????????float?sal?=?rs.getFloat(5);??
30. ????????????emp?=?new?Emp();??????????????emp.setEmpno(empno);??
31. ????????????emp.setEname(ename);??????????????emp.setJob(job);??
32. ????????????emp.setHireDate(rs.getDate(4));??????????????emp.setSal(sal);??
33. ????????}??????????return?emp;??
34. ????}??}??

5.EmpDAOProxy.java

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1. package?org.dao.impl;??import?org.dao.*;??
2. import?java.sql.*;??import?org.vo.*;??
3. import?java.util.*;??import?org.dbc.*;??
4. public?class?EmpDAOProxy?implements?IEmpDAO{??????private?DatabaseConnection?dbc;??
5. ????private?IEmpDAO?dao?=?null;??????public?EmpDAOProxy()throws?Exception{??
6. ????????dbc?=?new?DatabaseConnection();??????????dao?=?new?EmpDAOImpl(dbc.getConnection());??
7. ????}??????public?boolean?doCreate(Emp?emp)throws?Exception{??
8. ????????boolean?flag?=?false;??????????if(dao.findById(emp.getEmpno())==null){??
9. ????????????flag?=?dao.doCreate(emp);??????????}??
10. ????????dbc.close();??????????return?flag;??
11. ????}??????public?List<Emp>?findAll()throws?Exception{??
12. ????????List<Emp>list?=?dao.findAll();??????????dbc.close();??
13. ????????return?list;??????}??
14. ????public?Emp?findById(int?empno)throws?Exception{??????????Emp?emp?=?dao.findById(empno);??
15. ????????dbc.close();??????????return?emp;??
16. ????}??}??

6.DAOFactory.java

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1. package?org.dao.factory;??import?org.dao.*;??
2. import?java.sql.*;??import?org.vo.*;??
3. import?java.util.*;??import?org.dbc.*;??
4. import?org.dao.impl.*;??public?class?DAOFactory{??
5. ????public?static?IEmpDAO?getInstance(){??????????IEmpDAO?dao?=?null;??
6. ????????try{??????????????dao?=?new?EmpDAOProxy();??????
7. ????????}??????????catch(Exception?e){??
8. ????????????e.printStackTrace();??????????}??
9. ????????return?dao;??????}??
10. }??

7.TestDAO.java

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1. package?org.dao.test;??import?org.dao.factory.*;??
2. import?org.vo.*;??import?org.dao.*;??
3. public?class?TestDAO{??????public?static?void?main(String?args[])throws?Exception{??
4. ????????Emp?emp?=?null;??????????for(int?i=0;i<5;i++){??
5. ????????????emp?=?new?Emp();??????????????emp.setEmpno(i);??
6. ????????????emp.setEname("xiazdong-"+i);??????????????emp.setJob("stu-"+i);??
7. ????????????emp.setHireDate(new?java.util.Date());??????????????emp.setSal(500*i);??
8. ????????????DAOFactory.getInstance().doCreate(emp);??????????}??
9. ????}??}??

通过DAO设计模式，可以在JSP中屏蔽了数据库连接的操作，达到JSP只负责显示的效果。

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