Javaweb-Dao方法

Dao

Dao(Data Access Object 数据存储对象)：Java和数据库打交道的代码，jdbc是dao的一种表现形式

位于业务逻辑和持久化数据之间，实现对持久化数据的访问。

Dao在类和数据表之间起着转换器的作用，把实体类转化为数据库中的记录。

项目的结构：

（1）pojo/models实体类:存放所有数据库表的实体映射

package com.fruit.pojo;
public class Fruit {
    private int fid;
    private String fname;
    private int price;
    private int fcount;
    private String remark;
    public Fruit(){}
    public Fruit(int fid, String fname, int price, int fcount, String remark) {
        this.fid = fid;
        this.fname = fname;
        this.price = price;
        this.fcount = fcount;
        this.remark = remark;
    }
    public int getFid() {
        return fid;
    }
    public void setFid(int fid) {
        this.fid = fid;
    }
    public void setFname(String fname) {
        this.fname = fname;
    }
    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {this.price = price;}
    public int getFcount() {
        return fcount;
    }
    public void setFcount(int fcount) {
        this.fcount = fcount;
    }
    public String getRemark() {
        return remark;
    }
    public void setRemark(String remark) {
        this.remark = remark;
    }
    public String getFname() {
        return fname;
    }
    @Override
    public String toString() {
        return "水果{" +
                "编号=" + fid +
                ", 名字='" + fname + '\'' +
                ", 价格=" + price +
                ", 重量=" + fcount +
                ", 备注='" + remark + '\'' +
                '}';
    }
}

（2）tools工具类：存放DB.java（连接数据库的方法）、db.properties（数据库连接信息）

package com.fruit.tools;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class DB {
    //4个数据库参数
     static String driver = null;
     static String url = null;
     static String name = null;
     static String pwd = null;
     
    //3个操作对象
    protected Connection conn = null;
    protected PreparedStatement ps = null;
    protected ResultSet rs = null;
    
    //2个方法
    public void getConn() {
        try {
            Class.forName(driver);
            conn = DriverManager.getConnection(url,name,pwd);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public void close()  {
        if(rs!=null) {
            try {
                rs.close();
                if(ps!=null)
                    ps.close();
                if(conn!=null)
                    conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    
    //1个静态代码块
    static {
        InputStream is = DB.class.getClassLoader().getResourceAsStream("db.properties");
        Properties pp = new Properties();
        try {
            pp.load(is);
            driver = pp.getProperty("driver");
            url = pp.getProperty("url");
            name = pp.getProperty("username");
            pwd = pp.getProperty("password");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

//db.properties
driver = com.mysql.cj.jdbc.Driver
url = jdbc:mysql://localhost:3306/mytest?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&useSSL=false&serverTimezone=GMT%2B8
username = root
password = 123456

（3）dao：存放Dao接口（XxxDao），里面定义对数据的操作方法，没有具体实现。

          存放Dao接口中操作的具体实现（XxxDaoImpl）。

package com.fruit.dao;

import com.fruit.pojo.Fruit;
import java.util.List;

//dao接口
public interface FruitDao {
    void add(Fruit f);
    void delete();
    void update();
    List<Fruit> findFruit();
}

package com.fruit.dao.impl;

import com.fruit.dao.FruitDao;
import com.fruit.pojo.Fruit;
import com.fruit.tools.DB;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

//接口的实现类
public class FruitDaoImpl extends DB implements FruitDao {
    @Override
    public void add(Fruit f) {
    String sql = "insert into fruit values(?,?,?,?,?)";
    getConn();
    try{
        ps = conn.prepareStatement(sql);
        ps.setInt(1,f.getFid());
        ps.setString(2,f.getFname());
        ps.setInt(3,f.getPrice());
        ps.setInt(4,f.getFcount());
        ps.setString(5,f.getRemark());
        ps.executeUpdate();
    }catch (Exception e) {
        e.printStackTrace();
    }finally {
        close();
    } }

    @Override
    public void delete() {
        getConn();
        String sql = "delete  from fruit where fid =?";
        try {
            ps = conn.prepareStatement(sql);
            ps.setInt(1, 4);
            ps.executeUpdate();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            close();
        }
    }

    @Override
    public void update() {
        getConn();
        String sql ="UPDATE fruit SET `remark`=? WHERE fid = ?";
        try {
            ps = conn.prepareStatement(sql);
            ps.setString(1,"很小");
            ps.setInt(2,2);
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            close();
        }
    }

    @Override
    public List<Fruit> findFruit() {
        List<Fruit> list = new ArrayList<>();
        getConn();
        String sql = "select * from fruit";
        try {
            ps = conn.prepareStatement(sql);
            rs = ps.executeQuery();
            while(rs.next()){
                Fruit fruit = new Fruit();
                fruit.setFid(rs.getInt(1));
                fruit.setFname(rs.getString(2));
                fruit.setPrice(rs.getInt(3));
                fruit.setFcount(rs.getInt(4));
                fruit.setRemark(rs.getString(5));
                list.add(fruit);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            close();
        }
        return list;
    }
}

（4）test：存放具体的测试类，XxxDao fd = new XxxDaoImpl(); //父类引用指向子类对象

package com.fruit.test;

import com.fruit.dao.FruitDao;
import com.fruit.dao.impl.FruitDaoImpl;
import com.fruit.pojo.Fruit;

public class TestAdd  {
    public static void main(String[] args) {
        FruitDao fd = new FruitDaoImpl(); //父类引用指向子类对象
        Fruit f = new Fruit();
        f.setFid(4);
        f.setFname("grape");
        f.setPrice(22);
        f.setFcount(3);
        f.setRemark("中等");
        fd.add(f);
    }
}
public class TestDelete {
    public static void main(String[] args) {
        FruitDao fd = new FruitDaoImpl();
        fd.delete();
    }
}
public class TestQuery {
    public static void main(String[] args) {
        FruitDao fruitDao = new FruitDaoImpl();
        List<Fruit> fruit = fruitDao.findFruit();
        for (int i = 0; i < fruit.size() ; i++) {
            System.out.println(fruit.get(i).toString());
        }
    }
}
public class TestUpdate {
    public static void main(String[] args) {
        FruitDao fruitDao = new FruitDaoImpl();
        fruitDao.update();
    }
}