SSH一些问题解决

1、jsp 清除session的方法（引自新浪博客/先知）

“就是关于如何清除当前页面的session 退出到首页，使用户再次登陆必须提供正确的用户名和密码

我的三个页面是 index.jsp logon.jsp logout.jsp

index.jsp中输入正确的用户名和密码会跳转到logon.jsp中

在logon.jsp中我加了以下内容防止在浏览器中输入logon.jsp非法登录

<%
String admin_name=(String) session.getValue("name");
if(admin_name==null)
out.print("<script>alert('请先登陆。');window.location.href='index.jsp';</script>");
%>

我在logon.jsp中有个链接"退出登陆"指向logout.jsp页面

logout.jsp的内容如下:

<%
session.invalidate();
out.print("<script>alert('用户即将退出，确定后退出该页面。');window.location.href='index.jsp'</script>");
%>

……“

然后自己测试时发现将 <%session.invalidate();%> 放在body的顶部会将需要得到的session也清除掉，而放在body尾部可以只清除当前旧的session并且不会清除将要得到的session。

2、hibernate 执行sql ,select 返回string long （引自CSDN博主/arui_email）

1.执行sql，返回一个结果集，适用查询一个字段并返回一条记录

public Long findSeqTbTest() {
String sql = "select SEQ_TB_TEST.nextval from dual";
SQLQuery query = this.getSession().createSQLQuery(sql);
String str = query.uniqueResult().toString();
return Long.valueOf(str);
}

//获取表中最小的id
String sql = "select min(a.employeeid) from Emplyees a";
Long id = (Long) session.createQuery(sql).uniqueResult();

//获取数据库时间mysql
String sql = "select now() from dual";
String time =  session.createSQLQuery(sql).uniqueResult().toString();

2.删除、更新等操作，这里参数是从0开始的

public void deleteTbTest(Long id) {
String hql = "DELETE FROM TbTest WHERE ID = ?";
this.getSession().createQuery(hql).setLong(0, id).executeUpdate();
}

public void updateTbTest(Date date, boolean flag) {
String sql = "update tb_test set t_name=? where t_status!=1 and t_date" + (flag ? "<?" : "=?");
SQLQuery query = this.getSession().createSQLQuery(sql);
query.setString(0,flag ? "hello": "hi").setDate(1, date).executeUpdate();
}

3.执行sql，查询单表中多条数据

//尽量避免适用"*"
String sql = "select * from employee e where e.valid=1 and not exists (select employeeid from attendance a where a.employeeid=e.employeeid and a.date = ?)";
SQLQuery query = getSession().createSQLQuery(sql);
query.addEntity(Employee.class).setDate(0, day);
List<Employee> retList = query.list();

4.查询多表

String hql = "select new map(dept.deptID as deptID,dept.depNo as deptNo,dept.deptName as deptName,emp.empName as empName,emp.empID as empID,emp.empAge as age,emp.empNo as empNo) from Department dept ,Employee emp where dept.depID = emp.depID and emp.empName = ? and emp.sex = ?";
return getHibernateTemplate().find(hql, new Object[] { name, sex });

每个字段都保存在map中（key是字段名，value是此字段的值如：[{empID=1,empName=leona,…},…]）

5.查询多表

String sql = "select dept.deptID as deptID,dept.depNo as deptNo,dept.deptName as deptName,emp.empName as empName,emp.empID as empID,emp.empAge as age,emp.empNo as empNo,emp.birthday as birthday from Employee emp LEFT JOIN Department dept on dept.depID = emp.depID where empName = ?";
return (List<EmpBean>) this.getSession()
.createSQLQuery(sql)
.addScalar("deptID", Hibernate.STRING)
.addScalar("deptNo", Hibernate.STRING)
.addScalar("deptName", Hibernate.STRING)
.addScalar("empName", Hibernate.STRING)
.addScalar("empID", Hibernate.STRING)
.addScalar("age", Hibernate.LONG)
.addScalar("birthday", Hibernate.DATE)
.addScalar("empNo", Hibernate.STRING)
.setString(0, empName)
// 将结果集映射为EmpBean对象
.setResultTransformer(Transformers.aliasToBean(EmpBean.class)).list();

String hql = "from Attendance att where att.employeeid = ? and att.date =? ";
List<Attendance> list = this.getHibernateTemplate().find(hql,
new Object[] { employeeid, workDay });
if (null != list && !list.isEmpty()) {
return list.get(0);
}

String queryString = "FROM Attendance a WHERE a.employeeid=? AND DATE_FORMAT(a.date,'%Y-%m')=DATE_FORMAT(?,'%Y-%m') ORDER BY a.teamname";
Query queryObject = getSession(). createQuery(queryString);
queryObject.setParameter(0, id);
queryObject.setParameter(1, date);
return queryObject.list();

Session session = getSession();
session.clear();
getSession().saveOrUpdate(transientInstance);

startBatch()的用法

public class LocalDaoImpl extends SqlMapClientDaoSupport implements LocalDao {

public void insertBuNaTaxBatLst(final PaginatedList list)
{
getSqlMapClientTemplate().execute(new SqlMapClientCallback() {
public Object doInSqlMapClient(SqlMapExecutor executor)
throws SQLException {
executor.startBatch();
// do some iBatis operations here
for(int i=0,count=list.size();i<count;i++)
{
executor.insert("insertBuNaTaxBatLst", list.get(i));
if (i % 50 == 0) {
System.out.println("----" + i);//没有意义只为测试
}
}
executor.executeBatch();
return null;
}
});
}

3.删除某条记录（有其他表的外键）时报错Cannot delete or update a parent row: a foreign key constraint fails

删除（one端）某条记录（有其他表的外键）时页面报错“……Cannot delete or update a parent row: a foreign key constraint fails……”
查了一下原因发现是数据库中另一个表（many或one）的删除时选项默认是“SET NULL",在外键约束下需要改为CASCADE，即级联删除。这样当删除one端的数据时many端也会同时删除。
![数据库——设计表，改外键删除时的策略为CASCADE](http://img.blog.csdn.net/20160406003826078)

HQL：from Project o where 1=1 and PRJ_NAME like '%strCond%'；//这里PRJ_NAME 应该是数据库表中的实际字段名

HQL：from Project o where 1=1 and o.PRJ_NAME like '%strCond%'；//这里PRJ_NAME 应该是实体类的属性名

HQL：from Project o where 1=1 and PRJ_NAME like '？'；//这里的？不视为占位参数

HQL：from Project o where 1=1 and PRJ_NAME like ？；//设置参数值时会自动在参数值两边加上单引号。