JDBC之多表联查获取数据的操作案例

package com.ape.dao.ImpI; import com.ape.bean.BanJi; import com.ape.bean.student; import com.ape.dao.BaseDao; import com.ape.dao.DaoUtil; import com.ape.dao.IBanJiDao; import sun.invoke.util.BytecodeName; import java.util.ArrayList; import java.util.List; public class BanJiDaoImpI extends BaseDao implements IBanJiDao { @Override public List<BanJi> findAllBanJiAndStudent() { List<BanJi> bjList = new ArrayList<BanJi>(); String sql = "select * from class left join student on class.classid = student.classid"; try { rs = query(sql); while (rs.next()) { int index = -1; //获取集合中找到班级的下标 for (int i = 0; i < bjList.size(); i++) { if (rs.getInt("classid") == bjList.get(i).getClassid()) { index = i; break; } } if (index == -1) { //班级从来没有出现过才需要new班级 BanJi bj = new BanJi(); bj.setClassid(rs.getInt("classid")); bj.setClassname(rs.getString("classname")); student s = new student(); s.setBirth(rs.getDate("birthday")); s.setClassid(rs.getInt("classid")); s.setSid(rs.getInt("sid")); s.setSname(rs.getString("sname")); s.setSsex(rs.getString("ssex")); List<student> sList = new ArrayList<student>(); sList.add(s); bj.setsList(sList); bjList.add(bj); }else { student s = new student(); s.setBirth(rs.getDate("birthday")); s.setClassid(rs.getInt("classid")); s.setSid(rs.getInt("sid")); s.setSname(rs.getString("sname")); s.setSsex(rs.getString("ssex")); List<student> sList = new ArrayList<student>(); sList.add(s); BanJi banJi = bjList.get(index); banJi.getsList().add(s); } } } catch (Exception e) { e.printStackTrace(); } finally { DaoUtil.closeResource(connection, preparedStatement, rs); } return bjList; } }