JDBC系列教材 （十）- 基于JDBC设计DAO的实例

DAO=DataAccess Object

数据访问对象

实际上就是运用了练习-ORM中的思路，把数据库相关的操作都封装在这个类里面，其他地方看不到JDBC的代码

步骤1:DAO接口
步骤2:HeroDAO
步骤3:练习-ItemDAO
步骤4:答案-ItemDAO

步骤 1 : DAO接口

package jdbc;

  

import java.util.List;

import charactor.Hero;

  

public interface DAO{

    //增加

    public void add(Hero hero);

    //修改

    public void update(Hero hero);

    //删除

    public void delete(int id);

    //获取

    public Hero get(int id);

    //查询

    public List<Hero> list();

    //分页查询

    public List<Hero> list(int start, int count);

}

步骤 2 : HeroDAO

设计类HeroDAO，实现接口DAO

这个HeroDAO和答案-ORM很接近，做了几个改进：
1. 把驱动的初始化放在了构造方法HeroDAO里：

public HeroDAO() {

    try {

        Class.forName("com.mysql.jdbc.Driver");

    } catch (ClassNotFoundException e) {

        e.printStackTrace();

    }

}

因为驱动初始化只需要执行一次，所以放在这里更合适，其他方法里也不需要写了，代码更简洁

2. 提供了一个getConnection方法返回连接
所有的数据库操作都需要事先拿到一个数据库连接Connection，以前的做法每个方法里都会写一个，如果要改动密码，那么每个地方都需要修改。 通过这种方式，只需要修改这一个地方就可以了。 代码变得更容易维护，而且也更加简洁。

package jdbc;

  

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.ArrayList;

import java.util.List;

  

import charactor.Hero;

  

public class HeroDAO implements DAO{

  

    public HeroDAO() {

        try {

            Class.forName("com.mysql.jdbc.Driver");

        } catch (ClassNotFoundException e) {

            e.printStackTrace();

        }

    }

  

    public Connection getConnection() throws SQLException {

        return DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root",

                "admin");

    }

  

    public int getTotal() {

        int total = 0;

        try (Connection c = getConnection(); Statement s = c.createStatement();) {

  

            String sql = "select count(*) from hero";

  

            ResultSet rs = s.executeQuery(sql);

            while (rs.next()) {

                total = rs.getInt(1);

            }

  

            System.out.println("total:" + total);

  

        } catch (SQLException e) {

  

            e.printStackTrace();

        }

        return total;

    }

  

    public void add(Hero hero) {

  

        String sql = "insert into hero values(null,?,?,?)";

        try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

  

            ps.setString(1, hero.name);

            ps.setFloat(2, hero.hp);

            ps.setInt(3, hero.damage);

  

            ps.execute();

  

            ResultSet rs = ps.getGeneratedKeys();

            if (rs.next()) {

                int id = rs.getInt(1);

                hero.id = id;

            }

        } catch (SQLException e) {

  

            e.printStackTrace();

        }

    }

  

    public void update(Hero hero) {

  

        String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";

        try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

  

            ps.setString(1, hero.name);

            ps.setFloat(2, hero.hp);

            ps.setInt(3, hero.damage);

            ps.setInt(4, hero.id);

  

            ps.execute();

  

        } catch (SQLException e) {

  

            e.printStackTrace();

        }

  

    }

  

    public void delete(int id) {

  

        try (Connection c = getConnection(); Statement s = c.createStatement();) {

  

            String sql = "delete from hero where id = " + id;

  

            s.execute(sql);

  

        } catch (SQLException e) {

  

            e.printStackTrace();

        }

    }

  

    public Hero get(int id) {

        Hero hero = null;

  

        try (Connection c = getConnection(); Statement s = c.createStatement();) {

  

            String sql = "select * from hero where id = " + id;

  

            ResultSet rs = s.executeQuery(sql);

  

            if (rs.next()) {

                hero = new Hero();

                String name = rs.getString(2);

                float hp = rs.getFloat("hp");

                int damage = rs.getInt(4);

                hero.name = name;

                hero.hp = hp;

                hero.damage = damage;

                hero.id = id;

            }

  

        } catch (SQLException e) {

  

            e.printStackTrace();

        }

        return hero;

    }

  

    public List<Hero> list() {

        return list(0, Short.MAX_VALUE);

    }

  

    public List<Hero> list(int start, int count) {

        List<Hero> heros = new ArrayList<Hero>();

  

        String sql = "select * from hero order by id desc limit ?,? ";

  

        try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

  

            ps.setInt(1, start);

            ps.setInt(2, count);

  

            ResultSet rs = ps.executeQuery();

  

            while (rs.next()) {

                Hero hero = new Hero();

                int id = rs.getInt(1);

                String name = rs.getString(2);

                float hp = rs.getFloat("hp");

                int damage = rs.getInt(4);

                hero.id = id;

                hero.name = name;

                hero.hp = hp;

                hero.damage = damage;

                heros.add(hero);

            }

        } catch (SQLException e) {

  

            e.printStackTrace();

        }

        return heros;

    }

  

}

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