dwr和jsp实现的三级联动菜单

package com.dao; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.util.ArrayList; import java.util.List; import com.db.Connection; import com.vo.City; import com.vo.Country; import com.vo.Province; /******************************************************************************* * 核心dao，所有的查询方法都写在这(只是示例嘛，就写在了一个dao里面，个人比较懒) * * @author zdw * */ @SuppressWarnings("unchecked") public class CountryDAO { /** * 查询所有国家 */ public List queryAll() { java.sql.Connection conn = Connection.getInstance().open(); String sql = "select * from country"; List list = new ArrayList(); try { PreparedStatement pstmt = conn.prepareStatement(sql); ResultSet rs = pstmt.executeQuery(); while (rs.next()) { Country country = new Country(); country.setId(rs.getInt("id")); country.setCountryName(rs.getString("countryName")); list.add(country); } } catch (SQLException e) { e.printStackTrace(); } return list; } /*************************************************************************** * 根据coutryId查询出旗下的省 * * @param countryId * @return */ public List queryProvinceById(Integer countryId) { java.sql.Connection conn = Connection.getInstance().open(); String sql = "select * from province where countryId = ?"; List list = new ArrayList(); try { PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setInt(1, countryId); ResultSet rs = pstmt.executeQuery(); while (rs.next()) { Province province = new Province(); province.setId(rs.getInt("id")); province.setProvinceName(rs.getString("provinceName")); list.add(province); } } catch (SQLException e) { e.printStackTrace(); } return list; } /*************************************************************************** * 根据省id查询所有城市 * * @param provinceId * @return */ public List queryCityById(Integer provinceId) { java.sql.Connection conn = Connection.getInstance().open(); String sql = "select * from city where provinceId = ?"; List list = new ArrayList(); try { PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setInt(1, provinceId); ResultSet rs = pstmt.executeQuery(); while (rs.next()) { City city = new City(); city.setId(rs.getInt("id")); city.setCityName(rs.getString("cityName")); list.add(city); } } catch (SQLException e) { e.printStackTrace(); } return list; } // 测试dao的输出方法 public static void p(Object o) { System.out.println(o); } public static void main(String[] args) { CountryDAO countryDAO = new CountryDAO(); p(countryDAO.queryAll()); p(countryDAO.queryProvinceById(1)); p(countryDAO.queryCityById(2)); } }