对于DAO的代码优化

迷南。 2022-08-09 01:55 98阅读 0赞

对于[`UserDaoJdbcImp.java`][UserDaoJdbcImp.java] 存在着很多的冗余代码，现在对其进行一下优化：

将公共的部分提取到超类中，不同的部分由子类负责。

1、超类

package cn.itcast.dao.refactor;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    import cn.itcast.dao.Impl.DaoException;
    import cn.itcast.jdbc.JdbcUtils;
    
    //跟具体的类没有关系
    public abstract class AbstractDao { 
    
        public int update(String sql, Object[] args) { 
            Connection conn = null;
            PreparedStatement ps = null;
            ResultSet rs = null;
    
            try {
                conn = JdbcUtils.getConnection();
                ps = conn.prepareStatement(sql);
                for (int i = 0; i < args.length; i++) {
                    ps.setObject(i + 1, args[i]);
                }
                return ps.executeUpdate();
            } catch (SQLException e) {
                throw new DaoException(e.getMessage(), e);
            } finally {
                JdbcUtils.free(rs, ps, conn);
            }
        }
    
        public Object find(String sql, Object[] args) {
            Connection conn = null;
            PreparedStatement ps = null;
            ResultSet rs = null;
    
            try {
                conn = JdbcUtils.getConnection();
                ps = conn.prepareStatement(sql);
                for (int i = 0; i < args.length; i++) {
                    ps.setObject(i + 1, args[i]);
                }
                rs = ps.executeQuery();
                Object obj = null;
                while (rs.next()) { // 超类无法处理结果集
                    obj = rowMapper(rs);
                }
                return obj;
            } catch (SQLException e) {
                throw new DaoException(e.getMessage(), e);
            } finally {
                JdbcUtils.free(rs, ps, conn);
            }
        }
    
        abstract protected Object rowMapper(ResultSet rs)throws SQLException;
    }

2、子类，以User为例

package cn.itcast.dao.refactor;
    
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    import cn.itcast.domain.User;
    
    public class UserDaoImpl extends AbstractDao{ 
    
        public static void main(String[] args) {
    
        }
    
        public User findUser(String loginName,String password){
            String sql="select id,name,money,birthday from user where name=?";
            Object[]args=new Object[]{loginName};
            return (User)super.find(sql, args);
        }
    
        protected Object rowMapper(ResultSet rs)throws SQLException{
            User user=new User();
            user.setId(rs.getInt("id"));
            user.setName(rs.getString("name"));
            user.setMoney(rs.getFloat("money"));
            user.setBirthday(rs.getDate("birthday"));
            return user;
        }
    
        public void update(User user) {
            String sql="update user set name=?,birthday=?,money=? where id=?";
            Object[]args=new Object[]{user.getName(),user.getBirthday(),user.getMoney(),user.getId()};
            super.update(sql, args);
        }
    
        public void delete(User user){  //删除其实就是更新
            String sql="delete from user where id=?";
            Object[]args=new Object[]{user.getId()};
            super.update(sql, args);
    
        }
    }

[UserDaoJdbcImp.java]: http://blog.csdn.net/taoxiuxia/article/details/48814607