jdbc采用前后端分离的web项目

package dao; import entity.Item; import util.DBHelper; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.util.ArrayList; public class ItemDao { //获得所有商品的信息 public ArrayList<Item> getAllItems() { Connection conn = null; PreparedStatement stmt = null; ResultSet rs = null; //数据集 ArrayList<Item> list = new ArrayList<>();// 商品集合 //对数据库操作容易出现异常 try { conn = DBHelper.getConnection(); String sql = "select * from item";// SQL语句 stmt = conn.prepareStatement(sql); rs = stmt.executeQuery(); while (rs.next()) { Item item = new Item(); item.setId(rs.getInt("id")); item.setName(rs.getString("name")); item.setCity(rs.getString("city")); item.setNumber(rs.getInt("number")); item.setPrice(rs.getInt("price")); item.setPicture(rs.getString("picture")); list.add(item); // 把一个商品加入集合 } return list; // 返回集合。 } catch (Exception e) { e.printStackTrace(); return null; } finally { //释放资源 //不要释放连接conn，因为是单例模式对象，释放了之后的方法都没办法使用。 // 释放数据集对象rs if (rs != null) { try { rs.close(); rs = null; } catch (Exception ex) { ex.printStackTrace(); } } // 释放语句对象 if (stmt != null) { try { stmt.close(); stmt = null; } catch (Exception ex) { ex.printStackTrace(); } } } } // 根据商品编号获得商品信息 public Item getItemsById(int id) { Connection conn = null; PreparedStatement stmt = null; ResultSet rs = null; try { conn = DBHelper.getConnection(); String sql = "select * from item where id=?;"; // SQL语句：传一个id stmt = conn.prepareStatement(sql); stmt.setInt(1, id); rs = stmt.executeQuery(); if (rs.next()) { Item item = new Item(); item.setId(rs.getInt("id")); item.setName(rs.getString("name")); item.setCity(rs.getString("city")); item.setNumber(rs.getInt("number")); item.setPrice(rs.getInt("price")); item.setPicture(rs.getString("picture")); return item; } else { return null; } } catch (Exception ex) { ex.printStackTrace(); return null; } finally { // 释放数据集对象 if (rs != null) { try { rs.close(); rs = null; } catch (Exception ex) { ex.printStackTrace(); } } // 释放语句对象 if (stmt != null) { try { stmt.close(); stmt = null; } catch (Exception ex) { ex.printStackTrace(); } } } } //获取最近浏览的前五条商品信息 public ArrayList<Item> getViewList(String list) { System.out.println("list:" + list); ArrayList<Item> itemList = new ArrayList<>(); int iCount = 5; //每次返回前五条记录 if (list != null && list.length() > 0) { String[] arr = list.split("#"); //保存的是字符串类型，需要转换成整型 //V1：返回前五条记录，所以要判断，优化入v2 // for (String s : arr) { // int id = Integer.parseInt(s); // itemList.add(getItemsById(id)); // } // return itemList; //V2 if (arr.length >= 5) { for (int i = arr.length - 1; i >= arr.length - iCount; i--) { itemList.add(getItemsById(Integer.parseInt(arr[i]))); } } else { for (int i = arr.length - 1; i >= 0; i--) { itemList.add(getItemsById(Integer.parseInt(arr[i]))); } } return itemList; } else { return null; } } }