Java自学-JDBC DAO

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

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

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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