[jdbc]DAO及相关实现类

osc_jklrr90y 2020-11-08 12:56:54
java


DAO

  1. DAO:Data Access Object访问数据信息的类和接口,包括了对数据的CRUD(Create、Retrival、Update、Delete),而不包含任何业务相关的信息。有时也称作:BaseDAO
  2. 作用:为了实现功能的模块化,更有利于代码的维护和升级。

3.具体

  • BaseDAO: 我们用BaseDAO作为我们要实现业务的类的父类
  • CustomerDAO接口:我们要实现什么功能就造什么接口定义规范,主要针对于customer表的常用操作
  • CustomerDAOImpl:然后再实现这个接口,进行具体的增删改查操作
    在这里插入图片描述

BaseDAO.java

package com.flora2.dao;
import com.flora.util.JDBCUtils;
import java.lang.reflect.Field;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
/**
* @author flora
* @create 2020-11-06 20:42
*/
public class BaseDAO {

//通用的增删改操作 (考虑事务)
public void update(Connection connection, String sql, Object ...args){

PreparedStatement ps = null;
try {

//1. 预编译sql语句,返回PreparedStatement的实例
ps = connection.prepareStatement(sql);
//2. 填充占位符
for (int i = 0; i < args.length; i++) {

ps.setObject(i+1,args[i]);
}
//3. 执行
ps.execute();
} catch (Exception e) {

e.printStackTrace();
} finally {

//4. 资源的关闭
JDBCUtils.closeResource(null,ps);
}
}
//通用的查询操作,用于返回数据表中的一条记录 考虑事务
public <T>T getInstance(Connection connection,Class<T> clazz, String sql,Object... args){

PreparedStatement ps = null;
ResultSet resultSet = null;
try {

ps = connection.prepareStatement(sql);
for (int i = 0; i < args.length; i++) {

ps.setObject(i+1,args[i]);
}
resultSet = ps.executeQuery();
//获取结果集的元数据
ResultSetMetaData rsmd = resultSet.getMetaData();
//通过ResultSetMetaData获取结果集的列数
int columnCount = rsmd.getColumnCount();
if(resultSet.next()){

T t = clazz.newInstance();
//处理结果集一行数据的每一个列
for (int i = 0; i < columnCount; i++) {

//获取列值
Object columValue = resultSet.getObject(i + 1);
//获取每个列的列名
//String columnName = rsmd.getColumnName(i + 1);
String columnLabel = rsmd.getColumnLabel(i + 1);
//给t对象的指定的columnName属性,columValue 通过反射
Field field = clazz.getDeclaredField(columnLabel);
field.setAccessible(true);
field.set(t,columValue);
}
return t;
}
} catch (Exception e) {

e.printStackTrace();
} finally {

JDBCUtils.closeResource(null,ps,resultSet);
}
return null;
}
// 通用的查询操作,用于返回表中的多条数据的集合 考虑事务
public <T> List<T> getForList(Connection connection, Class<T> clazz, String sql, Object... args){

PreparedStatement ps = null;
ResultSet resultSet = null;
try {

connection = JDBCUtils.getConnection();
ps = connection.prepareStatement(sql);
for (int i = 0; i < args.length; i++) {

ps.setObject(i+1,args[i]);
}
resultSet = ps.executeQuery();
//获取结果集的元数据
ResultSetMetaData rsmd = resultSet.getMetaData();
//通过ResultSetMetaData获取结果集的列数
int columnCount = rsmd.getColumnCount();
//创建集合对象
ArrayList<T> list = new ArrayList<T>();
while(resultSet.next()){

T t = clazz.newInstance();
//处理结果集一行数据的每一个列;给t对象指定的属性赋值
for (int i = 0; i < columnCount; i++) {

//获取列值
Object columValue = resultSet.getObject(i + 1);
//获取每个列的列名
//String columnName = rsmd.getColumnName(i + 1);
String columnLabel = rsmd.getColumnLabel(i + 1);
//给t对象的指定的columnName属性,columValue 通过反射
Field field = clazz.getDeclaredField(columnLabel);
field.setAccessible(true);
field.set(t,columValue);
}
list.add(t);
}
return list;
} catch (Exception e) {

e.printStackTrace();
} finally {

JDBCUtils.closeResource(null,ps,resultSet);
}
return null;
}
//用于查询特殊值的通用方法
public <E>E getValue(Connection connection,String sql, Object...args){

PreparedStatement ps = null;
ResultSet rs = null;
try {

ps = connection.prepareStatement(sql);
for (int i = 0; i < args.length; i++) {

ps.setObject(i+1,args[i]);
}
rs = ps.executeQuery();
if(rs.next()){

return (E)rs.getObject(1);
}
} catch (SQLException throwables) {

throwables.printStackTrace();
} finally {

JDBCUtils.closeResource(null,ps,rs);
}
return null;
}
}

CustomerDAO.java

接口 定义规范

package com.flora2.dao;
import com.flora.bean.Customer;
import java.sql.Connection;
import java.sql.Date;
import java.util.List;
/**
* 此接口用来规范针对于customer表的常用操作
* @author flora
* @create 2020-11-06 20:57
*/
public interface CustomerDAO {

//将customer对象添加到数据库中
void insert(Connection connection, Customer customer);
//针对指定的id,删除表中的一条记录
void deleteById(Connection connection,int id);
//针对内存中的customer对象,去修改数据表中指定的记录
void update(Connection connection,Customer customer);
//针对指定的id查询得到的对应的Customer对象
Customer getCustomerById(Connection connection, int id);
//查询表中的所有记录构成的集合
List<Customer> getAll(Connection connection);
//返回数据表中的数据的条目数
Long getCount(Connection connection);
Date getMaxBirth(Connection connection);
}

CustomerDAOImpl.java

package com.flora2.dao;
import com.flora.bean.Customer;
import java.sql.Connection;
import java.sql.Date;
import java.util.List;
/**
* @author flora
* @create 2020-11-06 21:09
*/
public class CustomerDAOImpl extends BaseDAO implements CustomerDAO{

@Override
public void insert(Connection connection, Customer customer) {

String sql = "insert into customers(name,email,birth)values(?,?,?)";
update(connection,sql,customer.getName(),customer.getEmail(),customer.getBirth());
}
@Override
public void deleteById(Connection connection, int id) {

String sql = "delete from customers where id=?";
update(connection,sql,id);
}
@Override
public void update(Connection connection, Customer customer) {

String sql = "update customers set name=?,email=?,birth=? where id=?";
update(connection,sql,customer.getName(),customer.getEmail(),customer.getBirth(),customer.getId());
}
@Override
public Customer getCustomerById(Connection connection, int id) {

String sql = "select id,name,email,birth from customers where id=?";
Customer customer = getInstance(connection, Customer.class,sql, id);
return customer;
}
@Override
public List<Customer> getAll(Connection connection) {

String sql = "select id,name,email,birth from customers";
List<Customer> list = getForList(connection, Customer.class, sql);
return list;
}
@Override
public Long getCount(Connection connection) {

String sql = "select count(*) from customers";
return getValue(connection,sql);
}
@Override
public Date getMaxBirth(Connection connection) {

String sql = "select max(birth) from customers";
return getValue(connection,sql);
}
}

测试CustomerDAOImplTest

没写完 懒得写

package com.flora2.dao.junit;
import com.flora.bean.Customer;
import com.flora.util.JDBCUtils;
import com.flora2.dao.CustomerDAOImpl;
import java.sql.Connection;
import java.sql.Date;
import static org.junit.jupiter.api.Assertions.*;
/**
* @author flora
* @create 2020-11-06 21:31
*/
class CustomerDAOImplTest {

CustomerDAOImpl dao = new CustomerDAOImpl();
@org.junit.jupiter.api.Test
void insert() {

Connection connection = null;
try {

connection = JDBCUtils.getConnection();
Customer customer = new Customer(1,"于小飞","xiaofei@1265.com",new Date(47842892892829L));
dao.insert(connection,customer);
System.out.println("添加成功");
} catch (Exception e) {

e.printStackTrace();
} finally {

JDBCUtils.closeResource(connection,null);
}
}
@org.junit.jupiter.api.Test
void deleteById() {

}
@org.junit.jupiter.api.Test
void update() {

}
@org.junit.jupiter.api.Test
void getCustomerById() {

}
@org.junit.jupiter.api.Test
void getAll() {

}
@org.junit.jupiter.api.Test
void getCount() {

}
@org.junit.jupiter.api.Test
void getMaxBirth() {

}
}

升级版就是把Customer.class 去掉,具体没写, 再jdbc的第45集

版权声明
本文为[osc_jklrr90y]所创,转载请带上原文链接,感谢
https://my.oschina.net/u/4415966/blog/4708148

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