外卖平台JDBC项目中BusinessDAO层编写示例

在外卖平台JDBC项目中，BusinessDAO层主要负责与数据库进行交互，完成商家相关的数据操作。以下是BusinessDAO层的代码示例：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class BusinessDAO {
    // 查询所有商家
    public List<Business> getAllBusiness() {
        List<Business> businesses = new ArrayList<>();
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            conn = DBUtil.getConnection();
            String sql = 'select * from business';
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            while (rs.next()) {
                Business business = new Business();
                business.setId(rs.getInt('id'));
                business.setName(rs.getString('name'));
                business.setAddress(rs.getString('address'));
                business.setPhone(rs.getString('phone'));
                business.setDeliveryFee(rs.getDouble('delivery_fee'));
                businesses.add(business);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, stmt, rs);
        }
        return businesses;
    }

    // 根据商家id查询商家
    public Business getBusinessById(int id) {
        Business business = null;
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            conn = DBUtil.getConnection();
            String sql = 'select * from business where id = ?';
            stmt = conn.prepareStatement(sql);
            stmt.setInt(1, id);
            rs = stmt.executeQuery();
            if (rs.next()) {
                business = new Business();
                business.setId(rs.getInt('id'));
                business.setName(rs.getString('name'));
                business.setAddress(rs.getString('address'));
                business.setPhone(rs.getString('phone'));
                business.setDeliveryFee(rs.getDouble('delivery_fee'));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, stmt, rs);
        }
        return business;
    }

    // 添加商家
    public boolean addBusiness(Business business) {
        boolean flag = false;
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DBUtil.getConnection();
            String sql = 'insert into business(name, address, phone, delivery_fee) values(?, ?, ?, ?)';
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, business.getName());
            stmt.setString(2, business.getAddress());
            stmt.setString(3, business.getPhone());
            stmt.setDouble(4, business.getDeliveryFee());
            int rows = stmt.executeUpdate();
            if (rows > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, stmt);
        }
        return flag;
    }

    // 更新商家信息
    public boolean updateBusiness(Business business) {
        boolean flag = false;
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DBUtil.getConnection();
            String sql = 'update business set name=?, address=?, phone=?, delivery_fee=? where id=?';
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, business.getName());
            stmt.setString(2, business.getAddress());
            stmt.setString(3, business.getPhone());
            stmt.setDouble(4, business.getDeliveryFee());
            stmt.setInt(5, business.getId());
            int rows = stmt.executeUpdate();
            if (rows > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, stmt);
        }
        return flag;
    }

    // 删除商家
    public boolean deleteBusiness(int id) {
        boolean flag = false;
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DBUtil.getConnection();
            String sql = 'delete from business where id=?';
            stmt = conn.prepareStatement(sql);
            stmt.setInt(1, id);
            int rows = stmt.executeUpdate();
            if (rows > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, stmt);
        }
        return flag;
    }
}

以上代码中，getAllBusiness()方法用于查询所有商家信息，并返回一个Business对象列表。getBusinessById()方法根据商家id查询商家信息。addBusiness()方法用于添加商家信息到数据库中。updateBusiness()方法用于更新商家信息。deleteBusiness()方法用于删除商家信息。所有方法都使用了DBUtil类中提供的getConnection()方法获取数据库连接，并在使用完毕后调用close()方法关闭数据库连接。