hibernate对连接池的支持和HQL查询

2022-10-04 13:10:37

hibernate对连接池的支持

连接池，

作用：管理连接；提升连接的利用效率！

常用的连接池： C3P0连接池

Hibernate 自带的也有一个连接池，且对C3P0连接池也有支持！

只维护一个连接，比较简陋。

可以查看hibernate.properties文件查看连接池详细配置:

......
#################################
### Hibernate Connection Pool ###
#################################

# Hibernate自带的连接池：只有一个连接
hibernate.connection.pool_size 1

###########################
### C3P0 Connection Pool###
###########################
#Hibernate连接池的参数
#hibernate.c3p0.max_size 2  最大连接数
#hibernate.c3p0.min_size 2  最小连接数
#hibernate.c3p0.timeout 5000  超时连接
#hibernate.c3p0.max_statements 100  最大执行的命令个数
#hibernate.c3p0.idle_test_period 3000 空闲测试时间
#hibernate.c3p0.acquire_increment 2 连接不够用的时候，每次增加的连接数
#hibernate.c3p0.validate false

##############################
### Proxool Connection Pool###
##############################

## Properties for external configuration of Proxool

hibernate.proxool.pool_alias pool1

## Only need one of the following

#hibernate.proxool.existing_pool true
#hibernate.proxool.xml proxool.xml
#hibernate.proxool.properties proxool.properties

#################################
### Plugin ConnectionProvider ###
#################################

## use a custom ConnectionProvider (if not set, Hibernate will choose a built-in ConnectionProvider using hueristics)
#Hibernate对C3P0的连接池支持
#hibernate.connection.provider_class org.hibernate.connection.DriverManagerConnectionProvider
#hibernate.connection.provider_class org.hibernate.connection.DatasourceConnectionProvider
#hibernate.connection.provider_class org.hibernate.connection.C3P0ConnectionProvider
#hibernate.connection.provider_class org.hibernate.connection.ProxoolConnectionProvider

......

Hibernate.cfg.xml 中增加连接池相关配置：

　　　　　　　　　　<!-- 连接池配置 -->
		<!-- 配置连接驱动管理类 -->
		<property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
		<!-- 配置连接池参数信息 -->
		<property name="hibernate.c3p0.min_size">2</property>
		<property name="hibernate.c3p0.max_size">4</property>
		<property name="hibernate.c3p0.timeout">5000</property>
		<property name="hibernate.c3p0.max_statements">10</property>	<!-- 最大执行sql语句的条数 -->
		<property name="hibernate.c3p0.idle_test_period">3000</property>
		<property name="hibernate.c3p0.acquire_increment">2</property>

HQL查询

1、分页查询

@Test
	public void test() {
		Session session=sf.openSession();
		session.beginTransaction();

		Query query=session.createQuery("from Employee");

		//从记录数
		ScrollableResults scroll=query.scroll();	//得到滚动的结果集
		scroll.last();								//滚到最后一条
		int totalCount=scroll.getRowNumber()+1;		//得到滚动的记录数，即总记录数

		//设置分页参数
		query.setFirstResult(0);
		query.setMaxResults(4);
		List<Employee> list=query.list();

		for (Employee employee : list) {
			System.out.println(employee);
		}

		session.getTransaction().commit();
		session.close();

	}

2、HQL的各种查询

@Test
	public void testHql() {
		Session session=sf.openSession();
		session.beginTransaction();
		//查询指定的列
//		Query query=session.createQuery("select e.empId,e.empName from Employee e");

		//查询指定的列，同时自动封装【必须要提供带参数的构造器】
//		Query query=session.createQuery("select new Employee(e.empId,e.empName) from Employee e");

		//条件查询  一个条件/多个条件/ or /and /like模糊查询
		//占位符
//		Query query=session.createQuery("from Employee where empName=?");
//		query.setString(0, "王五");
		//条件查询，命名参数
//		Query query=session.createQuery("from Employee where empId=:myId and empName=:myName");
//		query.setParameter("myId", 3);
//		query.setParameter("myName", "王五");
		//模糊查询
//		Query query=session.createQuery("from Employee where empName like ?");
//		query.setString(0, "%王%");

		//聚合函数统计
//		Query query=session.createQuery("select count(*) from Employee");
//		Long num=(Long)query.uniqueResult();
//		System.out.println(num);

		//分组查询
		Query query=session.createQuery("select e.dept,count(*) from Employee e group by e.dept");

		System.out.println(query.list());
		session.getTransaction().commit();
		session.close();
	}

js：多级菜单

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效果连接：延迟菜单、

代码：链接

码农公寓

hibernate对连接池的支持

HQL查询

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