Hibernate之分页查询

HQL和QBC的Query,Criteria接口都提供分页查询设置，SQL检索方式使用所对应的数据库分页方式进行分页，

oracle用rownum,mysql用limit.

主要靠以下方法：

setFirstResult(firstResult)：从什么对象位置开始检索，默认参数值为0

setMaxResults(maxResults)：最多检出的数据条数，有多少检出多少，但是不能超过最大检出数据，设定的检出数据上限值。

1.HQL分页查询实例：

package com.lanhuigu.hibernate.test;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.lanhuigu.hibernate.entity.Customer;

public class TestHQL {
	public static void main(String[] args) throws Exception{
		Configuration cfg = new Configuration().configure();
		SessionFactory sessionFactory = cfg.buildSessionFactory();
		Session session = sessionFactory.openSession();
		Transaction tr = session.beginTransaction();
		//1.创建Query对象与
		Query query = session.createQuery("from Customer order by name desc");//降序,desc不可以去掉，去掉就升序了
		//2.命名参数动态绑定查询条件
		//query.setString("v_name", "test");
		//3.分页
		query.setFirstResult(0);//从什么位置开始，默认为0
		query.setMaxResults(1);//最多检出的条数
		//4.执行SQL
		List list = query.list();
		//5.输出结果
		for (int i = 0;i<list.size();i++) {
			Customer customer = (Customer) list.get(i);
			System.out.println(customer.getName());
		}
		//6.事务提交
		tr.commit();
		//7.关闭session
		session.close();
	}
}

执行结果：

Hibernate: select customer0_.ID as ID1_0_, customer0_.NAME as NAME2_0_, customer0_.EMAIL as EMAIL3_0_, customer0_.PASSWORD as PASSWORD4_0_, customer0_.PHONE as PHONE5_0_, customer0_.ADDRESS as ADDRESS6_0_, customer0_.SEX as SEX7_0_, customer0_.IS_MARRIED as IS8_0_, customer0_.DESCRIPTION as DESCRIPT9_0_, customer0_.IMAGE as IMAGE10_0_, customer0_.BIRTHDAY as BIRTHDA11_0_, customer0_.REGISTERED_TIME as REGISTE12_0_, customer0_.HOME_PROVINCE as HOME13_0_, customer0_.HOME_CITY as HOME14_0_, customer0_.HOME_STREET as HOME15_0_, customer0_.HOME_ZIPCODE as HOME16_0_, customer0_.COMP_PROVINCE as COMP17_0_, customer0_.COMP_CITY as COMP18_0_, customer0_.COMP_STREET as COMP19_0_, customer0_.COMP_ZIPCODE as COMP20_0_ from CUSTOMERS customer0_ order by customer0_.NAME desc limit ?
test

实例解释：

从0开始检索，最多检出1条。

2.QBC分页查询实例：

package com.lanhuigu.hibernate.test;

import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Criterion;
import org.hibernate.criterion.Expression;
import org.hibernate.criterion.Order;

import com.lanhuigu.hibernate.entity.Customer;

public class TestQBC {
	public static void main(String[] args) throws Exception{
		Configuration cfg = new Configuration().configure();
		SessionFactory sessionFactory = cfg.buildSessionFactory();
		Session session = sessionFactory.openSession();
		Transaction tr = session.beginTransaction();
		//1.创建Criteria对象
		Criteria criteria = session.createCriteria(Customer.class);
		//2.Expression静态方法绑定查询条件，创建的每个Criterion实例就是一个条件
		/*Criterion criterion = Expression.eq("name", "test");
		criteria.add(criterion);*/
		//3.排序
		//criteria.addOrder(Order.asc("name"));//升序
		criteria.addOrder(Order.desc("name"));//降序
		//4.分页
		criteria.setFirstResult(0);//从什么位置开始，默认为0
		criteria.setMaxResults(1);//最多检出的条数
		//5.执行SQL
		List list = criteria.list();
		//6.输出结果
		for (int i = 0;i<list.size();i++) {
			Customer customer = (Customer) list.get(i);
			System.out.println(customer.getName());
		}
		//7.事务提交
		tr.commit();
		//8.关闭session
		session.close();
	}
}

实例解释：

从0开始检索，最多检出1条

总结：

在执行结果控制台打印的sql中，结尾部分可以看到limit分页的身影，因为我用的mysql数据库。

分页的实质最后还是靠数据库。

在以上执行的sql中，limit后面可以看到一个'?'(limit ?),因为我设定从0开始检索，数据库默认也是从0开始的，

所以，limit就只有一个参数，第一个参数默认为0。

但是，当我将setFirstResult(1)设置成1，表示从1开始检索时，这个时候再次执行，结果如下：

Hibernate: select customer0_.ID as ID1_0_, customer0_.NAME as NAME2_0_, customer0_.EMAIL as EMAIL3_0_, customer0_.PASSWORD as PASSWORD4_0_, customer0_.PHONE as PHONE5_0_, customer0_.ADDRESS as ADDRESS6_0_, customer0_.SEX as SEX7_0_, customer0_.IS_MARRIED as IS8_0_, customer0_.DESCRIPTION as DESCRIPT9_0_, customer0_.IMAGE as IMAGE10_0_, customer0_.BIRTHDAY as BIRTHDA11_0_, customer0_.REGISTERED_TIME as REGISTE12_0_, customer0_.HOME_PROVINCE as HOME13_0_, customer0_.HOME_CITY as HOME14_0_, customer0_.HOME_STREET as HOME15_0_, customer0_.HOME_ZIPCODE as HOME16_0_, customer0_.COMP_PROVINCE as COMP17_0_, customer0_.COMP_CITY as COMP18_0_, customer0_.COMP_STREET as COMP19_0_, customer0_.COMP_ZIPCODE as COMP20_0_ from CUSTOMERS customer0_ order by customer0_.NAME desc limit ?, ?
hha

明显能看到生成sql后limit后面有两个问号（limit ?, ?)，就是用来接受我设置的分页的值，不是0，就不能按默认处理。