客戶層-------顯示層-------業(yè)務(wù)層---------數(shù)據(jù)層---------數(shù)據(jù)庫(kù)
1.客戶層：客戶層就是客戶端，簡(jiǎn)單的來(lái)說(shuō)就是瀏覽器。
2.顯示層：jsp/Servlet，用于給瀏覽器顯示。
3.業(yè)務(wù)層：對(duì)于數(shù)據(jù)層的原子操作進(jìn)行整合。
4.數(shù)據(jù)層：對(duì)于數(shù)據(jù)庫(kù)進(jìn)行的原子操作，增加、刪除等；
DAO應(yīng)用在數(shù)據(jù)層那塊,用于訪問(wèn)數(shù)據(jù)庫(kù)，對(duì)數(shù)據(jù)庫(kù)進(jìn)行操作的類。
DAO設(shè)計(jì)模式一般分為幾個(gè)類：
1.VO(Value Object)：一個(gè)用于存放網(wǎng)頁(yè)的一行數(shù)據(jù)即一條記錄的類，比如網(wǎng)頁(yè)要顯示一個(gè)用戶的信息，則這個(gè)類就是用戶的類。
2.DatabaseConnection：用于打開(kāi)和關(guān)閉數(shù)據(jù)庫(kù)。
3.DAO接口：用于聲明對(duì)于數(shù)據(jù)庫(kù)的操作。
4.DAOImpl：必須實(shí)現(xiàn)DAO接口，真實(shí)實(shí)現(xiàn)DAO接口的函數(shù)，但是不包括數(shù)據(jù)庫(kù)的打開(kāi)和關(guān)閉。
5.DAOPRoxy：也是實(shí)現(xiàn)DAO接口，但是只需要借助DAOImpl即可，但是包括數(shù)據(jù)庫(kù)的打開(kāi)和關(guān)閉。
6.DAOFactory：工廠類，含有g(shù)etInstance()創(chuàng)建一個(gè)Proxy類。
DAO的好處就是提供給用戶的接口只有DAO的接口，所以如果用戶想添加數(shù)據(jù)，只需要調(diào)用create函數(shù)即可，不需要數(shù)據(jù)庫(kù)的操作。
對(duì)于DAO，包的命名和類的命名一定要有層次。
1.Emp.java VO類
[java] view plaincopy package org.vo; import java.util.*; public class Emp{ private int empno; private String ename; private String job; private Date hireDate; private float sal; public Emp(){ } public int getEmpno(){ return empno; } public void setEmpno(int empno){ this.empno = empno; } public String getEname(){ return ename; } public void setEname(String ename){ this.ename = ename; } public Date getHireDate(){ return hireDate; } public void setHireDate(Date hireDate){ this.hireDate = hireDate; } public float getSal(){ return sal; } public void setSal(float sal){ this.sal = sal; } public String getJob(){ return job; } public void setJob(String job){ this.job = job; } }
2.DatabaseConnection.java 連接數(shù)據(jù)庫(kù)操作
package org.dbc; import java.sql.*; public class DatabaseConnection{ private Connection con = null; private static final String DRIVER = "com.MySQL.jdbc.Driver"; private static final String USER = "root"; private static final String URL = "jdbc:mysql://localhost:3306/mldn"; private static final String PASS = "12345"; public DatabaseConnection()throws Exception{ Class.forName(DRIVER); con = DriverManager.getConnection(URL,USER,PASS); } public Connection getConnection()throws Exception{ return con; } public void close()throws Exception{ if(con!=null){ con.close(); } } }
3.IEmpDAO.java dao接口
package org.dao; import java.util.List; import org.vo.*; public interface IEmpDAO{ public boolean doCreate(Emp emp)throws Exception; public List<Emp> findAll()throws Exception; public Emp findById(int empno)throws Exception; }
4.EmpDAOImpl.java 接口的實(shí)現(xiàn)類
package org.dao.impl; import org.dao.*; import java.sql.*; import org.vo.*; import java.util.*; public class EmpDAOImpl implements IEmpDAO{ private Connection con; private PreparedStatement stat = null; public EmpDAOImpl(Connection con){ this.con = con; } public boolean doCreate(Emp emp)throws Exception{ String sql = "INSERT INTO emp(empno,ename,job,hiredate,sal) VALUES(?,?,?,?,?)"; stat = con.prepareStatement(sql); stat.setInt(1,emp.getEmpno()); stat.setString(2,emp.getEname()); stat.setString(3,emp.getJob()); stat.setDate(4,new java.sql.Date(emp.getHireDate().getTime())); stat.setFloat(5,emp.getSal()); int update = stat.executeUpdate(); if(update>0){ return true; } else{ return false; } } public List<Emp> findAll()throws Exception{ String sql = "SELECT empno,ename,job,hiredate,sal FROM emp"; stat = con.prepareStatement(sql); ResultSet rs = stat.executeQuery(); Emp emp = null; List<Emp> list = new ArrayList<Emp>(); while(rs.next()){ int empno = rs.getInt(1); String ename = rs.getString(2); String job = rs.getString(3); float sal = rs.getFloat(5); emp = new Emp(); emp.setEmpno(empno); emp.setEname(ename); emp.setJob(job); emp.setHireDate(rs.getDate(4)); emp.setSal(sal); list.add(emp); } return list; } public Emp findById(int empno)throws Exception{ String sql = "SELECT empno,ename,job,hiredate,sal FROM emp WHERE empno=?"; stat = con.prepareStatement(sql); stat.setInt(1,empno); ResultSet rs = stat.executeQuery(); Emp emp = null; if(rs.next()){ String ename = rs.getString(2); String job = rs.getString(3); float sal = rs.getFloat(5); emp = new Emp(); emp.setEmpno(empno); emp.setEname(ename); emp.setJob(job); emp.setHireDate(rs.getDate(4)); emp.setSal(sal); } return emp; } }
5.EmpDAOProxy.java 數(shù)據(jù)庫(kù)開(kāi)關(guān)
package org.dao.impl; import org.dao.*; import java.sql.*; import org.vo.*; import java.util.*; import org.dbc.*; public class EmpDAOProxy implements IEmpDAO{ private DatabaseConnection dbc; private IEmpDAO dao = null; public EmpDAOProxy()throws Exception{ dbc = new DatabaseConnection(); dao = new EmpDAOImpl(dbc.getConnection()); } public boolean doCreate(Emp emp)throws Exception{ boolean flag = false; if(dao.findById(emp.getEmpno())==null){ flag = dao.doCreate(emp); } dbc.close(); return flag; } public List<Emp> findAll()throws Exception{ List<Emp>list = dao.findAll(); dbc.close(); return list; } public Emp findById(int empno)throws Exception{ Emp emp = dao.findById(empno); dbc.close(); return emp; } }
6.DAOFactory.java 工廠類
package org.dao.factory; import org.dao.*; import java.sql.*; import org.vo.*; import java.util.*; import org.dbc.*; import org.dao.impl.*; public class DAOFactory{ public static IEmpDAO getInstance(){ IEmpDAO dao = null; try{ dao = new EmpDAOProxy(); } catch(Exception e){ e.printStackTrace(); } return dao; } }
7.TestDAO.java
通過(guò)DAO設(shè)計(jì)模式，可以在JSP中屏蔽了數(shù)據(jù)庫(kù)連接的操作，達(dá)到JSP只負(fù)責(zé)顯示的效果。
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