回顾

package orm.test;
import java.sql.*;
public class test {
    public static void main(String[] args) throws Exception {
        // 1.导包
        // 2.加载类驱动
        Class.forName("com.mysql.jdbc.Driver");
        // 3.获取连接
        String Host = "jdbc:mysql://bj-cdb-547s28hs.sql.tencentcdb.com:60439/test?useSSL=false";
        String user = "root";
        String password = "qq2653650997";
        Connection conn = DriverManager.getConnection(Host, user, password);
        // 4.创建状态参数
        // String sql = "insert into atm values (?,?,?)";
        String sql = "select * from atm";
        PreparedStatement pstat = conn.prepareStatement(sql);
        // 5.执行操作
        // pstat.setString(1,"李四");
        // pstat.setString(2,"123");
        // pstat.setFloat(3,700);
        // 增加数据
        // int count = pstat.executeUpdate();
        // 查询数据
        ResultSet resultSet = pstat.executeQuery(sql);
        while (resultSet.next()){
            String aname = resultSet.getString("aname");
            String apass = resultSet.getString("apassword");
            Float abalance = resultSet.getFloat("abalance");
            System.out.println(aname+"的银行密码是"+apass+",在银行存了"+abalance+"元");
        }
        // System.out.println(count+"行受到影响");
        // 6.关闭资源
        pstat.close();
        conn.close();
    }
}

缺点：通过上述代码可以看出，每当我们需要更新(查询)数据时都需要重新书写一遍”JDBC流程”，这样在日常开发中，会造成代码冗余，可读性不强。也不符合MVC的分层架构思想。 改进：通过封装来实现”JDBC”的复用使代码可读性增强，减少代码的冗余。

第一次优化

package orm.dao;
import orm.domain.Atm;
import java.sql.*;
public class AtmDao {
    private String className = "com.mysql.jdbc.Driver";
    private String Host = "";
    private String user = "";
    private String password = "";
    // 查询数据
    public Atm selectOne(String aname) {
        Atm atm = null;
        try {
            Class.forName(className);
            Connection conn = DriverManager.getConnection(Host, user, password);
            String sql = "select * from atm";
            PreparedStatement pstat = conn.prepareStatement(sql);
            // 查询数据
            ResultSet resultSet = pstat.executeQuery(sql);
            while (resultSet.next()) {
                atm = new Atm();
                atm.setAname(resultSet.getString("aname"));
                atm.setApassword(resultSet.getString("apassword"));
            }
            resultSet.close();
            pstat.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return atm;
    }
    // 更新数据
    public void update(Atm atm) {
        try {
            Class.forName(className);
            Connection conn = DriverManager.getConnection(Host, user, password);
            String sql = "update atm set apassword = ?,abalance = ? where aname = ?";
            PreparedStatement pstat = conn.prepareStatement(sql);
            pstat.setString(1, atm.getApassword());
            pstat.setFloat(2, atm.getAbalance());
            pstat.setString(3, atm.getAname());
            pstat.executeUpdate();
            pstat.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    // 新增数据
    public void insert(Atm atm) {
        try {
            Class.forName(className);
            Connection conn = DriverManager.getConnection(Host, user, password);
            String sql = "insert into atm values (?,?,?)";
            PreparedStatement pstat = conn.prepareStatement(sql);
            pstat.setString(1, atm.getAname());
            pstat.setString(2, atm.getApassword());
            pstat.setFloat(3, atm.getAbalance());
            pstat.executeUpdate();
            pstat.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    // 删除数据
    public void cancle(String aname) {
        try {
            Class.forName(className);
            Connection conn = DriverManager.getConnection(Host, user, password);
            String sql = "delete from atm where aname = ?";
            PreparedStatement pstat = conn.prepareStatement(sql);
            pstat.setString(1, aname);
            pstat.executeUpdate();
            pstat.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class AtmService {
    private AtmDao dao = new AtmDao();
    // 登陆
    public String login(String aname,String apassword){
        // 1.读取数据库
        Atm atm = dao.selectOne(aname);
        // 2.判断
        if (atm!=null && atm.getApassword().equals(apassword)){
            return "登陆成功";
        }
        else {
            return "账号或密码输入错误";
        }
    }
    // 查询
    public Float query(String aname){
        return dao.selectOne(aname).getAbalance();
    }
    // 存款
    public void deposit(String aname,Float money){
        Atm atm = dao.selectOne(aname);
        atm.setAbalance(atm.getAbalance() + money);
        dao.update(atm);
    }
    // 开户
    public void create(String aname,String apassword,Float abalance){
        Atm atm = new Atm(aname,apassword,abalance);
    }
    // 销户
    public void cancel(String anane){
        dao.cancle(anane);
    }
    // 取款,转账(参考存款)
}

第一次更新总结： service：每一个业务方法都不一样，对应着一个具体的逻辑(比较，计算，判断) dao：dao中的方法都是对数据库中的数据进行增删改查(JDBC+SQL)，也看出了dao中的方法大部分一样，存在冗余

第二次优化