[Java] DAO设计模式

背景

• B/S（Browser/Server）：浏览器/服务器架构，用于广域网
• C/S（Client/Server）：客户机/服务器架构，用于局域网
• 不同层之间没有任何的耦合问题，彼此都是依据协议或者接口标准结合在一起

 

业务分析

• 前端
• 控制层
  • 调用业务层
• 业务层（Business Object BO）
  • 调用数据层实现业务操作
  • 业务层需要明确地知道数据层的操作方法，但不需要知道它的具体实现
  • 使用代理模式（动态代理）进行业务控制，Sprint、Struct框架中会提供
  • 定义操作协议（接口）
  • 定义业务实现类，控制数据库的打开和关闭，取得数据层接口对象，调用数据层操作
  • 定义业务工厂类，用于供控制层实例化，隐藏具体实现
• 数据层（Data Access Object DAO，持久层）
  • 把具体的业务“翻译”成数据库的原子操作（增删改查）
  • 定义接口，对业务层隐藏子类，一个数据表对应一个接口
  • 定义简单Java类（POJO），对数据表中的数据进行包装，以便在不同层之间传递数据
  • 定义实现类，一个类实现一个接口，类中一个方法实现一个具体的SQL操作
  • 定义工厂类，用于其它层实例化接口对象，隐藏具体实现
• 数据库

 

 

实例

• 功能：连接mysql，为雇员表增加一行数据
• 每层只能和相邻层交互
• 每层结构都是：接口先行--子类实现--工厂解耦
• 项目结构：

代码

• 数据库连接类 -- DatabaseConnection.java

package dbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DatabaseConnection {
    private static final String DBDRIVER = "com.mysql.cj.jdbc.Driver";
    private static final String DBURL = "jdbc:mysql://127.0.0.1:3306/company?serverTimezone=GMT%2B8&characterEncoding=UTF-8&useSSL=false";
    private static final String DBUSER = "root";
    private static final String PASSWORD = "Chen1227+";
    private Connection conn = null;
    
    // 连接数据库
    public DatabaseConnection() {
        try {
            Class.forName(DBDRIVER);
        } catch (ClassNotFoundException e1) {
            e1.printStackTrace();
        }
        try {
            this.conn = DriverManager.getConnection(DBURL,DBUSER,PASSWORD);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    
    // 取得数据库的连接对象
    public Connection getConnection() {
        return this.conn;
    }
    
    // 关闭数据库
    public void close() {
        if(this.conn != null) {
            try {
                this.conn.close();
                //System.out.print("close success!");
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

• POJO类 -- Emp.java

package vo;

import java.io.Serializable;
import java.util.Date;


@SuppressWarnings("serial")
public class Emp implements Serializable{
    private Integer empno;
    private String ename;
    private String job;
    private Date hiredate;
    private Double sal;
    private Double comm;
    
    public Integer getEmpno() {
        return empno;
    }
    public void setEmpno(Integer empno) {
        this.empno = empno;
    }
    public String getEname() {
        return ename;
    }
    public void setEname(String name) {
        this.ename = name;
    }
    public String getJob() {
        return job;
    }
    public void setJob(String job) {
        this.job = job;
    }
    public Date getHiredate() {
        return hiredate;
    }
    public void setHiredate(Date hiredate) {
        this.hiredate = hiredate;
    }
    public Double getSal() {
        return sal;
    }
    public void setSal(Double sal) {
        this.sal = sal;
    }
    public Double getComm() {
        return comm;
    }
    public void setComm(Double comm) {
        this.comm = comm;
    }
}

• 数据层
  • 数据层接口 -- IEmpDAO.java

package dao;

import java.util.List;
import java.util.Set;

import vo.Emp;

public interface IEmpDAO {
    public boolean doCreate(Emp vo) throws Exception;
    public boolean doUpdata(Emp vo) throws Exception;
    public boolean doRemoveBatch(Emp vo) throws Exception;
    public boolean doRemoveBatch(Set<Integer> ids) throws Exception;
    public Emp findById(Integer id) throws Exception;
    public List<Emp> findAll() throws Exception;
    public List<Emp> findAll(Integer currentPage, Integer LineSize, String column, String keyWord) throws Exception;
    public Integer getAllCount(String column, String keyWord) throws Exception;
 }

• • 数据层实现类 -- EmpDAOImpl.java

package dao.impl;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.util.List;
import java.util.Set;

import dao.IEmpDAO;
import vo.Emp;

public class EmpDAOImpl implements IEmpDAO{
    private Connection conn;
    private PreparedStatement pstmt;
    
    public EmpDAOImpl(Connection conn) {
        this.conn = conn;
    }
    
    @Override
    public boolean doCreate(Emp vo) throws Exception {
        String sql = "INSERT INTO emp(empno,ename,job,hiredate,sal,comm) VALUES (?,?,?,?,?,?)";
        this.pstmt = this.conn.prepareStatement(sql);
        this.pstmt.setInt(1, vo.getEmpno());
        this.pstmt.setString(2, vo.getEname());
        this.pstmt.setString(3, vo.getJob());
        this.pstmt.setDate(4, new java.sql.Date(vo.getHiredate().getTime()));
        this.pstmt.setDouble(5, vo.getSal());
        this.pstmt.setDouble(6, vo.getComm());
        // System.out.println("insert success!");
        return this.pstmt.executeUpdate() > 0;
    }

    @Override
    public boolean doUpdata(Emp vo) throws Exception {
        return false;
    }

    @Override
    public boolean doRemoveBatch(Emp vo) throws Exception {
        return false;
    }

    @Override
    public boolean doRemoveBatch(Set<Integer> ids)
            throws Exception {
        return false;
    }

    @Override
    public Emp findById(Integer id) throws Exception {
        return null;
    }

    @Override
    public List<Emp> findAll() throws Exception {
        return null;
    }

    @Override
    public List<Emp> findAll(Integer currentPage,
            Integer LineSize, String column, String keyWord)
            throws Exception {
        return null;
    }

    @Override
    public Integer getAllCount(String column,
            String keyWord) throws Exception {
        return null;
    }
    
}

• • 数据层工厂类 -- DAOFactory.java

package factory;

import java.sql.Connection;
import dao.IEmpDAO;
import dao.impl.EmpDAOImpl;

public class DAOFactory {
    public static IEmpDAO getIEmpDAOInstance(Connection conn) {
        return new EmpDAOImpl(conn);
    }
}

• 业务层
  • 业务层接口 -- IEmpService.java

package service;
import vo.Emp;

public interface IEmpService {
    public boolean insert(Emp vo) throws Exception;
}

• • 业务层实现类 -- EmpServiceImpl.java

package service.impl;

import dbc.DatabaseConnection;
import factory.DAOFactory;
import service.IEmpService;
import vo.Emp;

public class EmpServiceImpl implements IEmpService{
    private DatabaseConnection dbc = new DatabaseConnection();

    @Override
    public boolean insert(Emp vo) throws Exception {
        try {
            if(DAOFactory.getIEmpDAOInstance(this.dbc.getConnection()).findById(vo.getEmpno()) == null ) {
                return DAOFactory.getIEmpDAOInstance(this.dbc.getConnection()).doCreate(vo);
            }
            System.out.println("insert false!");
            return false;
        }catch(Exception e) {
            throw e;
        }finally {
            this.dbc.close();
        }
    }
}

• • 业务层工厂类 -- ServiceFactory.java

package factory;

import service.IEmpService;
import service.impl.EmpServiceImpl;

public class ServiceFactory {
    public static IEmpService getIEmpServiceInstance() {
        return new EmpServiceImpl();
    }
}

• 测试类
  • main()测试

package test;

import java.util.Date;
import factory.ServiceFactory;
import vo.Emp;

public class TestEmpInsert {
    public static void main(String[] args) throws Exception{
        Emp vo = new Emp();
        vo.setEmpno(8888);
        vo.setEname("Lucy");
        vo.setJob("Teacher");
        vo.setHiredate(new Date());
        vo.setSal(8900.0);
        vo.setComm(5600.0);
        System.out.println(ServiceFactory.getIEmpServiceInstance().insert(vo));
    }
}

• • Junit测试

package test.junit;

import java.util.Date;
import org.junit.Test;
import factory.ServiceFactory;
import junit.framework.TestCase;
import vo.Emp;

public class IEmpServiceTest {
    
    @Test
    public void testInsert() throws Exception {
        Emp vo = new Emp();
        vo.setEmpno(8888);
        vo.setEname("Lucy");
        vo.setJob("Teacher");
        vo.setHiredate(new Date());
        vo.setSal(8900.0);
        vo.setComm(5600.0);
        TestCase.assertTrue(ServiceFactory.getIEmpServiceInstance().insert(vo));
    }
}

参考

B/S与C/S的区别

https://zhidao.baidu.com/question/3711387.html

java中PreparedStatement和Statement详细讲解

https://blog.csdn.net/czh500/article/details/88202971

class.forName()做了什么

https://blog.csdn.net/u012292938/article/details/81033660