1．首先看两个例子来比较一下
（1）在用Query方法查询的时候，通过HQL语句来得到Query对象，并对Query对象进行操作，首先是用list方法获取到Query的List集合并输出
public void listQuery() {
Configuration configuration =
new Configuration().configure();
SessionFactory factory = configuration.buildSessionFactory();
Session session = factory.openSession();
Query query =
session.createQuery("from Customers");
List<Customers> list =
query.list();
for(Customers entity:list){
System.out.println(entity.toString());
}
}
输出的结果为：
List的执行sql语句为：
Hibernate: select customers0_.id as id0_, customers0_.realName as realName0_, customers0_.pass as pass0_, customers0_.sex as sex0_, customers0_.petName as petName0_, customers0_.email as email0_, customers0_.rdate as rdate0_
from customers customers0_
[email protected]
（2）通过Query得到Query的对象，并用iterator迭代器输出
public void iterateQuery(){
Configuration configuration =
new Configuration().configure();
SessionFactory factory = configuration.buildSessionFactory();
Session session = factory.openSession();
Query query = session.createQuery("from Customers");
Iterator<Customers> it =
query.iterate();
// 遍历出来所有的查询结果
while (it.hasNext()) {
Customers customer = it.next();
System.out.println(customer.toString());
}
}
Iterator的执行结果：
Hibernate: select customers0_.id as col_0_0_ from customers customers0_
Hibernate: select customers0_.id as id0_0_, customers0_.realName as realName0_0_, customers0_.pass as pass0_0_, customers0_.sex as sex0_0_, customers0_.petName as petName0_0_, customers0_.email as email0_0_, customers0_.rdate
as rdate0_0_ from customers customers0_ where customers0_.id=?
[email protected]
结论：
（1） 从上面的执行结果可以看出获取的方式不一样
List的获取方式为：List<Customers> list =
query.list();
Iterator的获取方式：Iterator<Customers> it =
query.iterate();
（2）从执行结果可以看出list输出一条语句，而iterator输出的是两条sql语句，我们可想一下，为什么会输出这样的效果？
因为他们获取数据的方式不一样，list()会直接查询数据库，iterator()会先到数据库中把id都取出来，然后真正要遍历某个对象的时候先到缓存中找，如果找不到，以id为条件再发一条sql到数据库，这样如果缓存中没有数据，则查询数据库的次数为n+1次
（3）list只查询一级缓存，而iterator会从二级缓存中查
（4）list方法返回的对象都是实体对象，而iterator返回的是代理对象
（5) session中list第二次发出，仍会到数据库査询
（6) iterate 第二次，首先找session 级缓存