Hibernate延迟加载策略

　　所谓懒加载(lazy)就是延时加载，就是当在真正需要数据的时候，才真正执行数据加载操作

　　至于为什么要用懒加载呢，就是当我们要访问的数据量过大时，明显用缓存不太合适，因为内存容量有限，为了减少并发量，减少系统资源的消耗，我们让数据在需要的时候才进行加载，这时我们就用到了懒加载。

1.类级别的懒加载(session.load()方法)

　　get方法:没有任何策略.调用即立即查询数据库加载数据.

　　load方法: 应用类级别的加载策略

1.get方法测试，没有任何延迟加载策略

    @Test// get方法 : 立即加载.执行方法时立即发送sql语句查询结果public void fun1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------
        Customer customer = session.get(Customer.class, 1l);//执行完此句即查询发出SQL
        System.out.println(customer);//----------------------------------------------------
        tx.commit();session.close();}

　没有延迟加载的get方法执行时候就发出SQL请求，且生成的对象是原生的JavaBean对象。

2.load方法测试，测试懒加载策略

修改配置文件懒加载设为true，默认就是开启懒加载的.比如我们查询customer的时候不会查询linkman，而我们调用get方法获取linkman的时候才去获取linkman。

　　　　lazy(默认值):true, 查询类时,会返回代理对象.会在使用属性时,根据关联的session查询数据库.加载数据.

　　　　 lazy:false. load方法会与get方法没有任何区别.调用时即加载数据.

　　　　结论:为了提高效率.建议使用延迟加载(懒加载)

原理:

　　延迟加载是生成javaassist代理对象，生成代理对象的作用是依赖于session在使用对象的时候利用session去查询数据库，所以在使用懒加载时要确保,调用属性加载数据时,session还是打开的.不然会抛出异常

测试代码:

    @Test// load方法(默认):是在执行时,不发送任何sql语句.返回一个对象.使用该对象时,才执行查询.// 延迟加载: 仅仅获得没有使用.不会查询.在使用时才进行查询.// 是否对类进行延迟加载: 可以通过在class元素上配置lazy属性来控制.//lazy:true  加载时,不查询.使用时才查询//lazy:false 加载时立即查询.public void fun2(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------
        Customer customer = session.load(Customer.class, 1l);System.out.println(customer);//----------------------------------------------------
        tx.commit();session.close();}

查看生成的代理对象:(代理对象的名称后面带有$符号)

注意:我们在使用懒加载的时候不能再关闭session之后再使用对象，因为懒加载的代理对象依赖session再使用对象的时候查询数据库,如下面的代码是错误的:

    public void fun2(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------
        Customer customer = session.load(Customer.class, 1l);//----------------------------------------------------
        tx.commit();session.close();System.out.println(customer);}

结果会报错:

2.关联级别的查询(fetch、lazy、batch-size属性)

1.集合策略(根据客户关联查询联系人集合)

配置简介:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.qlq.domain" ><class name="Customer" table="cst_customer" ><id name="cust_id"  ><generator class="native"></generator></id><property name="cust_name" column="cust_name" ></property><property name="cust_source" column="cust_source" ></property><property name="cust_industry" column="cust_industry" ></property><property name="cust_level" column="cust_level" ></property><property name="cust_linkman" column="cust_linkman" ></property><property name="cust_phone" column="cust_phone" ></property><property name="cust_mobile" column="cust_mobile" ></property><!-- lazy属性: 决定是否延迟加载true(默认值): 延迟加载,懒加载false: 立即加载extra: 极其懒惰fetch属性: 决定加载策略.使用什么类型的sql语句加载集合数据select(默认值): 单表查询加载join: 使用多表查询加载集合subselect:使用子查询加载集合--><!-- batch-size: 抓取集合的数量为3.抓取客户的集合时,一次抓取几个客户的联系人集合.--><set name="linkMens"><key column="lkm_cust_id" ></key><one-to-many class="LinkMan" /></set></class>
</hibernate-mapping>

(1)fetch为select的测试:

lazy=true的测试

    // 集合级别的关联// fetch:select 单表查询// lazy:true 使用时才加载集合数据.
    @Testpublic void fun1() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
Customer c = session.get(Customer.class, 7l);Set<LinkMan> linkMens = c.getLinkMens();// 关联级别
System.out.println(linkMens);//打印SQL// ----------------------------------------------------
        tx.commit();session.close();}

SQL:

Hibernate: selectcustomer0_.cust_id as cust_id1_0_0_,customer0_.cust_name as cust_nam2_0_0_,customer0_.cust_source as cust_sou3_0_0_,customer0_.cust_industry as cust_ind4_0_0_,customer0_.cust_level as cust_lev5_0_0_,customer0_.cust_linkman as cust_lin6_0_0_,customer0_.cust_phone as cust_pho7_0_0_,customer0_.cust_mobile as cust_mob8_0_0_ fromcst_customer customer0_ wherecustomer0_.cust_id=?
Hibernate: selectlinkmens0_.lkm_cust_id as lkm_cus10_1_0_,linkmens0_.lkm_id as lkm_id1_1_0_,linkmens0_.lkm_id as lkm_id1_1_1_,linkmens0_.lkm_gender as lkm_gend2_1_1_,linkmens0_.lkm_name as lkm_name3_1_1_,linkmens0_.lkm_phone as lkm_phon4_1_1_,linkmens0_.lkm_email as lkm_emai5_1_1_,linkmens0_.lkm_qq as lkm_qq6_1_1_,linkmens0_.lkm_mobile as lkm_mobi7_1_1_,linkmens0_.lkm_memo as lkm_memo8_1_1_,linkmens0_.lkm_position as lkm_posi9_1_1_,linkmens0_.lkm_cust_id as lkm_cus10_1_1_ fromcst_linkman linkmens0_ wherelinkmens0_.lkm_cust_id=?
[LinkMan [lkm_id=3, lkm_gender=null, lkm_name=王八, lkm_phone=null, lkm_email=null, lkm_qq=null, lkm_mobile=null, lkm_memo=null, lkm_position=null, customer=Customer [cust_id=7, cust_name=测试名称1]], LinkMan [lkm_id=4, lkm_gender=null, lkm_name=田七, lkm_phone=null, lkm_email=null, lkm_qq=null, lkm_mobile=null, lkm_memo=null, lkm_position=null, customer=Customer [cust_id=7, cust_name=测试名称1]]]

lazy=false的测试(会立即加载)

    // 集合级别的关联// fetch:select 单表查询// lazy:false 立即记载集合数据
    @Testpublic void fun2() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
Customer c = session.get(Customer.class, 7l);//加载所有SQL，包括查询linkman
Set<LinkMan> linkMens = c.getLinkMens();// 关联级别
System.out.println(linkMens);// ----------------------------------------------------
        tx.commit();session.close();}

lazy=xetra极其懒惰，与懒加载效果基本一致. 如果只获得集合的size.只查询集合的size(count语句)

    // 集合级别的关联// fetch:select 单表查询// lazy:extra 极其懒惰.与懒加载效果基本一致. 如果只获得集合的size.只查询集合的size(count语句)
    @Testpublic void fun3() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
Customer c = session.get(Customer.class, 7l);Set<LinkMan> linkMens = c.getLinkMens();// 关联级别
System.out.println(linkMens.size());//count   SQL
System.out.println(linkMens);//查询SQL// ----------------------------------------------------
        tx.commit();session.close();}

SQL：

Hibernate: selectcustomer0_.cust_id as cust_id1_0_0_,customer0_.cust_name as cust_nam2_0_0_,customer0_.cust_source as cust_sou3_0_0_,customer0_.cust_industry as cust_ind4_0_0_,customer0_.cust_level as cust_lev5_0_0_,customer0_.cust_linkman as cust_lin6_0_0_,customer0_.cust_phone as cust_pho7_0_0_,customer0_.cust_mobile as cust_mob8_0_0_ fromcst_customer customer0_ wherecustomer0_.cust_id=?
Hibernate: selectcount(lkm_id) fromcst_linkman wherelkm_cust_id =?
2
Hibernate: selectlinkmens0_.lkm_cust_id as lkm_cus10_1_0_,linkmens0_.lkm_id as lkm_id1_1_0_,linkmens0_.lkm_id as lkm_id1_1_1_,linkmens0_.lkm_gender as lkm_gend2_1_1_,linkmens0_.lkm_name as lkm_name3_1_1_,linkmens0_.lkm_phone as lkm_phon4_1_1_,linkmens0_.lkm_email as lkm_emai5_1_1_,linkmens0_.lkm_qq as lkm_qq6_1_1_,linkmens0_.lkm_mobile as lkm_mobi7_1_1_,linkmens0_.lkm_memo as lkm_memo8_1_1_,linkmens0_.lkm_position as lkm_posi9_1_1_,linkmens0_.lkm_cust_id as lkm_cus10_1_1_ fromcst_linkman linkmens0_ wherelinkmens0_.lkm_cust_id=?

(2)fetch为join的多表查询: 延迟策略失效

    // 集合级别的关联// fetch:join 多表查询// lazy:true|false|extra 失效.立即加载.
    @Testpublic void fun4() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
Customer c = session.get(Customer.class, 7l);Set<LinkMan> linkMens = c.getLinkMens();// 关联级别
System.out.println(linkMens.size());System.out.println(linkMens);// ----------------------------------------------------
        tx.commit();session.close();}

SQL：

    selectcustomer0_.cust_id as cust_id1_0_0_,customer0_.cust_name as cust_nam2_0_0_,customer0_.cust_source as cust_sou3_0_0_,customer0_.cust_industry as cust_ind4_0_0_,customer0_.cust_level as cust_lev5_0_0_,customer0_.cust_linkman as cust_lin6_0_0_,customer0_.cust_phone as cust_pho7_0_0_,customer0_.cust_mobile as cust_mob8_0_0_,linkmens1_.lkm_cust_id as lkm_cus10_1_1_,linkmens1_.lkm_id as lkm_id1_1_1_,linkmens1_.lkm_id as lkm_id1_1_2_,linkmens1_.lkm_gender as lkm_gend2_1_2_,linkmens1_.lkm_name as lkm_name3_1_2_,linkmens1_.lkm_phone as lkm_phon4_1_2_,linkmens1_.lkm_email as lkm_emai5_1_2_,linkmens1_.lkm_qq as lkm_qq6_1_2_,linkmens1_.lkm_mobile as lkm_mobi7_1_2_,linkmens1_.lkm_memo as lkm_memo8_1_2_,linkmens1_.lkm_position as lkm_posi9_1_2_,linkmens1_.lkm_cust_id as lkm_cus10_1_2_ fromcst_customer customer0_ left outer joincst_linkman linkmens1_ on customer0_.cust_id=linkmens1_.lkm_cust_id wherecustomer0_.cust_id=?

(3)fetch为subselect (只有在批量查询的时候才有用，如果是查询单个的话与select的作用一样)

lazy为true

    @Test// fetch: subselect 子查询// lazy: true 懒加载public void fun5() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
String hql = "from Customer";Query query = session.createQuery(hql);List<Customer> list = query.list();for (Customer c : list) {System.out.println(c);System.out.println(c.getLinkMens().size());System.out.println(c.getLinkMens());}// ----------------------------------------------------
        tx.commit();session.close();}

SQL：

Hibernate: selectcustomer0_.cust_id as cust_id1_0_,customer0_.cust_name as cust_nam2_0_,customer0_.cust_source as cust_sou3_0_,customer0_.cust_industry as cust_ind4_0_,customer0_.cust_level as cust_lev5_0_,customer0_.cust_linkman as cust_lin6_0_,customer0_.cust_phone as cust_pho7_0_,customer0_.cust_mobile as cust_mob8_0_ fromcst_customer customer0_
Customer [cust_id=7, cust_name=测试名称1]
Hibernate: selectlinkmens0_.lkm_cust_id as lkm_cus10_1_1_,linkmens0_.lkm_id as lkm_id1_1_1_,linkmens0_.lkm_id as lkm_id1_1_0_,linkmens0_.lkm_gender as lkm_gend2_1_0_,linkmens0_.lkm_name as lkm_name3_1_0_,linkmens0_.lkm_phone as lkm_phon4_1_0_,linkmens0_.lkm_email as lkm_emai5_1_0_,linkmens0_.lkm_qq as lkm_qq6_1_0_,linkmens0_.lkm_mobile as lkm_mobi7_1_0_,linkmens0_.lkm_memo as lkm_memo8_1_0_,linkmens0_.lkm_position as lkm_posi9_1_0_,linkmens0_.lkm_cust_id as lkm_cus10_1_0_ fromcst_linkman linkmens0_ wherelinkmens0_.lkm_cust_id in (selectcustomer0_.cust_id fromcst_customer customer0_)

lazy为false，立即加载

    @Test// fetch: subselect 子查询// lazy: false 立即加载public void fun6() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
String hql = "from Customer";Query query = session.createQuery(hql);List<Customer> list = query.list();for (Customer c : list) {System.out.println(c);System.out.println(c.getLinkMens().size());System.out.println(c.getLinkMens());}// ----------------------------------------------------tx.commit();session.close();}

lazy为extra

    @Test// fetch: subselect 子查询// lazy: extra 极其懒惰public void fun7() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
String hql = "from Customer";Query query = session.createQuery(hql);List<Customer> list = query.list();for (Customer c : list) {System.out.println(c);System.out.println(c.getLinkMens().size());System.out.println(c.getLinkMens());}// ----------------------------------------------------
        tx.commit();session.close();}

SQL：

Hibernate: selectcustomer0_.cust_id as cust_id1_0_,customer0_.cust_name as cust_nam2_0_,customer0_.cust_source as cust_sou3_0_,customer0_.cust_industry as cust_ind4_0_,customer0_.cust_level as cust_lev5_0_,customer0_.cust_linkman as cust_lin6_0_,customer0_.cust_phone as cust_pho7_0_,customer0_.cust_mobile as cust_mob8_0_ fromcst_customer customer0_
Customer [cust_id=7, cust_name=测试名称1]
Hibernate: selectlinkmens0_.lkm_cust_id as lkm_cus10_1_1_,linkmens0_.lkm_id as lkm_id1_1_1_,linkmens0_.lkm_id as lkm_id1_1_0_,linkmens0_.lkm_gender as lkm_gend2_1_0_,linkmens0_.lkm_name as lkm_name3_1_0_,linkmens0_.lkm_phone as lkm_phon4_1_0_,linkmens0_.lkm_email as lkm_emai5_1_0_,linkmens0_.lkm_qq as lkm_qq6_1_0_,linkmens0_.lkm_mobile as lkm_mobi7_1_0_,linkmens0_.lkm_memo as lkm_memo8_1_0_,linkmens0_.lkm_position as lkm_posi9_1_0_,linkmens0_.lkm_cust_id as lkm_cus10_1_0_ fromcst_linkman linkmens0_ wherelinkmens0_.lkm_cust_id in (selectcustomer0_.cust_id fromcst_customer customer0_)

2.关联属性懒加载(先查询联系人，跟据联系人反查顾客)

XML配置:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.qlq.domain" ><class name="LinkMan" table="cst_linkman" ><id name="lkm_id"  ><generator class="native"></generator></id><property name="lkm_gender"  ></property><property name="lkm_name"  ></property><property name="lkm_phone"  ></property><property name="lkm_email"  ></property><property name="lkm_qq"  ></property><property name="lkm_mobile"  ></property><property name="lkm_memo"  ></property><property name="lkm_position"  ></property><!-- fetch 决定加载的sql语句select: 使用单表查询join : 多表查询 (会导致lazy失效)lazy  决定加载时机false: 立即加载proxy: 由customer的类级别加载策略决定.--><many-to-one name="customer" column="lkm_cust_id" class="Customer" fetch="select" lazy="proxy"></many-to-one></class>
</hibernate-mapping>

1.fetch为select,lazy为proxy,Customer类的lazy为true

测试代码:

    // 集合级别的关联// fetch:select 单表查询// lazy:proxy 代理，也就是由Customer的lazy属性决定是否懒加载//Customer的lazy为true
    @Testpublic void fun1() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
LinkMan linkMan = session.get(LinkMan.class, 5l);System.out.println("-------1------------");Customer customer = linkMan.getCustomer();System.out.println("-------2------------");System.out.println(customer);// 打印SQL// ----------------------------------------------------
        tx.commit();session.close();}

SQL：

Hibernate: selectlinkman0_.lkm_id as lkm_id1_1_0_,linkman0_.lkm_gender as lkm_gend2_1_0_,linkman0_.lkm_name as lkm_name3_1_0_,linkman0_.lkm_phone as lkm_phon4_1_0_,linkman0_.lkm_email as lkm_emai5_1_0_,linkman0_.lkm_qq as lkm_qq6_1_0_,linkman0_.lkm_mobile as lkm_mobi7_1_0_,linkman0_.lkm_memo as lkm_memo8_1_0_,linkman0_.lkm_position as lkm_posi9_1_0_,linkman0_.lkm_cust_id as lkm_cus10_1_0_ fromcst_linkman linkman0_ wherelinkman0_.lkm_id=?
-------1------------
-------2------------
Hibernate: selectcustomer0_.cust_id as cust_id1_0_0_,customer0_.cust_name as cust_nam2_0_0_,customer0_.cust_source as cust_sou3_0_0_,customer0_.cust_industry as cust_ind4_0_0_,customer0_.cust_level as cust_lev5_0_0_,customer0_.cust_linkman as cust_lin6_0_0_,customer0_.cust_phone as cust_pho7_0_0_,customer0_.cust_mobile as cust_mob8_0_0_ fromcst_customer customer0_ wherecustomer0_.cust_id=?
Customer [cust_id=9, cust_name=测试名称3]

2.fetch为select,lazy为proxy,Customer类的lazy为false

测试代码:

    // 集合级别的关联// fetch:select 单表查询// lazy:proxy 代理，也就是由Customer的lazy属性决定是否懒加载//Customer的lazy为false
    @Testpublic void fun2() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
        LinkMan linkMan = session.get(LinkMan.class, 5l);System.out.println("-------1------------");Customer customer = linkMan.getCustomer();System.out.println("-------2------------");System.out.println(customer);// 打印SQL// ----------------------------------------------------
        tx.commit();session.close();}

SQL：

Hibernate: selectlinkman0_.lkm_id as lkm_id1_1_0_,linkman0_.lkm_gender as lkm_gend2_1_0_,linkman0_.lkm_name as lkm_name3_1_0_,linkman0_.lkm_phone as lkm_phon4_1_0_,linkman0_.lkm_email as lkm_emai5_1_0_,linkman0_.lkm_qq as lkm_qq6_1_0_,linkman0_.lkm_mobile as lkm_mobi7_1_0_,linkman0_.lkm_memo as lkm_memo8_1_0_,linkman0_.lkm_position as lkm_posi9_1_0_,linkman0_.lkm_cust_id as lkm_cus10_1_0_ fromcst_linkman linkman0_ wherelinkman0_.lkm_id=?
Hibernate: selectcustomer0_.cust_id as cust_id1_0_0_,customer0_.cust_name as cust_nam2_0_0_,customer0_.cust_source as cust_sou3_0_0_,customer0_.cust_industry as cust_ind4_0_0_,customer0_.cust_level as cust_lev5_0_0_,customer0_.cust_linkman as cust_lin6_0_0_,customer0_.cust_phone as cust_pho7_0_0_,customer0_.cust_mobile as cust_mob8_0_0_ fromcst_customer customer0_ wherecustomer0_.cust_id=?
-------1------------
-------2------------
Customer [cust_id=9, cust_name=测试名称3]

3.fetch为join,lazy属性失效

代码:

    // 集合级别的关联// join 单表查询// lazy: 属性失效
    @Testpublic void fun3() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
        LinkMan linkMan = session.get(LinkMan.class, 5l);System.out.println("-------1------------");Customer customer = linkMan.getCustomer();System.out.println("-------2------------");System.out.println(customer);// 打印SQL// ----------------------------------------------------
        tx.commit();session.close();}

SQL:

Hibernate: selectlinkman0_.lkm_id as lkm_id1_1_0_,linkman0_.lkm_gender as lkm_gend2_1_0_,linkman0_.lkm_name as lkm_name3_1_0_,linkman0_.lkm_phone as lkm_phon4_1_0_,linkman0_.lkm_email as lkm_emai5_1_0_,linkman0_.lkm_qq as lkm_qq6_1_0_,linkman0_.lkm_mobile as lkm_mobi7_1_0_,linkman0_.lkm_memo as lkm_memo8_1_0_,linkman0_.lkm_position as lkm_posi9_1_0_,linkman0_.lkm_cust_id as lkm_cus10_1_0_,customer1_.cust_id as cust_id1_0_1_,customer1_.cust_name as cust_nam2_0_1_,customer1_.cust_source as cust_sou3_0_1_,customer1_.cust_industry as cust_ind4_0_1_,customer1_.cust_level as cust_lev5_0_1_,customer1_.cust_linkman as cust_lin6_0_1_,customer1_.cust_phone as cust_pho7_0_1_,customer1_.cust_mobile as cust_mob8_0_1_ fromcst_linkman linkman0_ left outer joincst_customer customer1_ on linkman0_.lkm_cust_id=customer1_.cust_id wherelinkman0_.lkm_id=?
-------1------------
-------2------------
Customer [cust_id=9, cust_name=测试名称3]

总结:

　　为了提高效率.fetch的选择上应选择select. lazy的取值应选择 true. 全部使用默认值.

3.批量抓取策略(batch-size属性)

　　此次略用于获取客户联系人的时候，一次抓取几个客户的联系人。此策略用于避免多次访问数据库，没有此策略是一次获取一个客户联系人，有了此策略可以一次获取多个客户的，减少访问数据库次数。

例如

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.qlq.domain" ><class name="Customer" table="cst_customer"><id name="cust_id"  ><generator class="native"></generator></id><property name="cust_name" column="cust_name" ></property><property name="cust_source" column="cust_source" ></property><property name="cust_industry" column="cust_industry" ></property><property name="cust_level" column="cust_level" ></property><property name="cust_linkman" column="cust_linkman" ></property><property name="cust_phone" column="cust_phone" ></property><property name="cust_mobile" column="cust_mobile" ></property><!-- lazy属性: 决定是否延迟加载true(默认值): 延迟加载,懒加载false: 立即加载extra: 极其懒惰fetch属性: 决定加载策略.使用什么类型的sql语句加载集合数据select(默认值): 单表查询加载join: 使用多表查询加载集合subselect:使用子查询加载集合--><!-- batch-size: 5   抓取集合的数量为5.抓取客户的集合时,一次抓取几个客户的联系人集合.--><set name="linkMens" batch-size="5"><key column="lkm_cust_id" ></key><one-to-many class="LinkMan" /></set></class>
</hibernate-mapping>

测试代码:

    public void fun5() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------
String hql = "from Customer";Query query = session.createQuery(hql);List<Customer> list = query.list();for (Customer c : list) {System.out.println(c.getLinkMens());}// ----------------------------------------------------
        tx.commit();session.close();}

SQL:

Hibernate: selectcustomer0_.cust_id as cust_id1_0_,customer0_.cust_name as cust_nam2_0_,customer0_.cust_source as cust_sou3_0_,customer0_.cust_industry as cust_ind4_0_,customer0_.cust_level as cust_lev5_0_,customer0_.cust_linkman as cust_lin6_0_,customer0_.cust_phone as cust_pho7_0_,customer0_.cust_mobile as cust_mob8_0_ fromcst_customer customer0_
Hibernate: selectlinkmens0_.lkm_cust_id as lkm_cus10_1_1_,linkmens0_.lkm_id as lkm_id1_1_1_,linkmens0_.lkm_id as lkm_id1_1_0_,linkmens0_.lkm_gender as lkm_gend2_1_0_,linkmens0_.lkm_name as lkm_name3_1_0_,linkmens0_.lkm_phone as lkm_phon4_1_0_,linkmens0_.lkm_email as lkm_emai5_1_0_,linkmens0_.lkm_qq as lkm_qq6_1_0_,linkmens0_.lkm_mobile as lkm_mobi7_1_0_,linkmens0_.lkm_memo as lkm_memo8_1_0_,linkmens0_.lkm_position as lkm_posi9_1_0_,linkmens0_.lkm_cust_id as lkm_cus10_1_0_ fromcst_linkman linkmens0_ wherelinkmens0_.lkm_cust_id in (?, ?, ?, ?, ?)
[LinkMan [lkm_id=4, lkm_gender=null, lkm_name=田七, lkm_phone=null, lkm_email=null, lkm_qq=null, lkm_mobile=null, lkm_memo=null, lkm_position=null, customer=Customer [cust_id=7, cust_name=测试名称1]], LinkMan [lkm_id=3, lkm_gender=null, lkm_name=王八, lkm_phone=null, lkm_email=null, lkm_qq=null, lkm_mobile=null, lkm_memo=null, lkm_position=null, customer=Customer [cust_id=7, cust_name=测试名称1]]]
[]
[LinkMan [lkm_id=5, lkm_gender=null, lkm_name=99, lkm_phone=null, lkm_email=null, lkm_qq=null, lkm_mobile=null, lkm_memo=null, lkm_position=null, customer=Customer [cust_id=9, cust_name=测试名称3]]]
[]
[]
Hibernate: selectlinkmens0_.lkm_cust_id as lkm_cus10_1_1_,linkmens0_.lkm_id as lkm_id1_1_1_,linkmens0_.lkm_id as lkm_id1_1_0_,linkmens0_.lkm_gender as lkm_gend2_1_0_,linkmens0_.lkm_name as lkm_name3_1_0_,linkmens0_.lkm_phone as lkm_phon4_1_0_,linkmens0_.lkm_email as lkm_emai5_1_0_,linkmens0_.lkm_qq as lkm_qq6_1_0_,linkmens0_.lkm_mobile as lkm_mobi7_1_0_,linkmens0_.lkm_memo as lkm_memo8_1_0_,linkmens0_.lkm_position as lkm_posi9_1_0_,linkmens0_.lkm_cust_id as lkm_cus10_1_0_ fromcst_linkman linkmens0_ wherelinkmens0_.lkm_cust_id in (?, ?, ?)

　　通过SQL看出获取客户联系人的时候一次获取5个客户的联系人，最后一次由于没有五个客户所以会查询剩余3个客户的联系人。

问题: no-session问题解决: 扩大session的作用范围.

　　在懒加载的策略中，我们通常是在Service层打开事务、session，service代码执行完毕只会进行提交或者回滚。但是我们的对象(代理对象)经常放在request域中带到页面进行显示，也就是到了页面才使用对象(查询数据库)，此时session已经关闭，如果使用了懒加载策略会报no-session异常。解决办法:过滤器扩大session作用范围(filter可以在请求执行前后都执行一些代码)，如下图逻辑:

　　其实SSH整合的时候spring已经做了过滤器来实现此功能，会在搭建SSH环境的时候介绍。