package org.programming.student;
import java.sql.*;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;
public class StudentsManagerImpl implements StudentsManager
{
public ArrayList<Student> getStudentList(java.util.Date beginDate, java.util.Date endDate)
{
String sql =
"select stu_id, class_name, c.class_id, stu_name, sex, birthday, contactTel, address"+
" from students stu join class c on stu.class_id = c.class_id "+
"where stu.birthday between ? and ?";
Connection conn = null;
PreparedStatement psmt = null;
ResultSet res = null;
ArrayList<Student> stu_list = new ArrayList<Student>();
try
{
conn = DBUtil.getConnection();
psmt = conn.prepareStatement(sql);
psmt.setDate(1, new java.sql.Date(beginDate.getTime()));
psmt.setDate(2, new java.sql.Date(endDate.getTime()));
res = psmt.executeQuery();
while(res.next())
{
Student student = new Student();
student.setStudentId(res.getString("stu_id"));
student.setName(res.getString("stu_name"));
student.setSex(res.getString("sex"));
student.setBirthday(res.getDate("birthday"));
student.setContactTel(res.getString("contacttel"));
student.setAddress(res.getString("address"));
Clas clas = new Clas();
clas.setClassName(res.getString("class_name"));
clas.setClassId(res.getString("class_id"));
student.setClas(clas);
stu_list.add(student);
}
}
catch(SQLException e)
{
e.printStackTrace();
}
return stu_list;
}
public static void main(String[] args) throws ParseException
{
StudentsManagerImpl stu_manager = new StudentsManagerImpl();
ArrayList<Student> list =
stu_manager.getStudentList(new SimpleDateFormat("yyyy-mm-dd").parse("1988-01-01"),
new SimpleDateFormat("yyyy-mm-dd").parse("1992-11-2"));
System.out.println("符合條件的學生人數爲:"+list.size());
for(Iterator<Student> iterator = list.iterator();iterator.hasNext();)
{
Student stu = iterator.next();
System.out.println(stu.getName());
}
}
}
在控制檯輸出的結果:
students整張表:
select * from students order by birthday;
調用和上述Java程序中相同的SQL語句:
alter session set nls_date_format = 'yyyy-mm-dd';
select stu_id, class_name, c.class_id, stu_name, sex, birthday, contactTel, address from students stu join class c on stu.class_id = c.class_id where stu.birthday between '1988-01-01' and '1992-11-2';
上述SQL語句在數據庫中所得結果:
在使用用java程序調用時,滿足條件的學生人數只有5個,而在Oracle數據庫中調用相同的SQL語句卻得到6個滿足條件的學生(這個是正確的),對比一下,是少了學生“旺財”,這搞的我很鬱悶。後來將我的問題發到論壇後,經過大家的指點,最終發現了我問題所在:方法SimpleDateFormat()的日期模式寫錯了,在類SimpleDateFormat的日期模式中,Month in year應該是大寫“M”,而我寫成了小寫,這樣一來就成了Minute in hour。小小的書寫錯誤,竟造成了整個業務邏輯上的錯誤,真是“差之毫釐謬以千里”啊!大家要引以爲戒。
另外,爲什麼在這種錯誤之下還能查詢出看似不賴的結果,由於我水平有限的很,自己百思不得其解。還希望大家能多多指教!