Spring CrudRepository throws org.hibernate.LazyInitializationException - spring

Question

i got a problem by using CrudRepository. Example: i have two entities, entity A has a collection of entity B.
class A {
int id;
int name;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
Set<B> bs;
// getters and setters
}
class B {
int id;
int name;
#ManyToOne(mappedBy="bs")
A a;
// getters and setters
}
then i got 2 repositories.
class ARepository extends CrudRepository<A, int>{}
class BRepository extends CrudRepository<B, int>{}
but when i got this, i got a org.hibernate.LazyInitializationException, how can i avoid this?
#Service
#Transactional(readOnly=true)
class ServiceImpl implements Service {
#Resource ARepository ar;
#Override
A a = ar.findOne(int id);
}
here is the applicationContext.xml:
<jpa:repositories base-package="com.myproject.repository" />
<context:component-scan base-package="com.myproject.*" />
<context:annotation-config />
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager" >
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="persistenceUnitName" value="keep-apm" />
<property name="jpaVendorAdapter">
<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="showSql" value="true" />
<property name="generateDdl" value="true" />
<property name="database" value="POSTGRESQL"/>
<property name="databasePlatform" value="org.hibernate.dialect.PostgreSQLDialect"/>
</bean>
</property>
</bean>
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="username" value="root" />
<property name="password" value="root" />
<property name="driverClassName" value="org.postgresql.Driver" />
<property name="url" value="jdbc:postgresql://127.0.0.1:5432/db" />
</bean>
<bean id="sessionFactory" factory-bean="entityManagerFactory" factory-method="getSessionFactory">
</bean>
<tx:annotation-driven transaction-manager="transactionManager" />
here is the web.xml
<filter>
<filter-name>openSessionInViewFilter</filter-name>
<filter-class>org.springframework.orm.hibernate4.support.OpenSessionInViewFilter</filter-class>
<init-param>
<param-name>singleSession</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>openSessionInViewFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<listener>
<listener-class>com.myproject.util.LogLocator</listener-class>
</listener>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
a.bs(the collection) would not be loaded, and always throw out a org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: no session or session was closed
Thank you in advance!!

Answer 1

You need to use start a transaction, preferably through Spring's Declarative Transaction Management.
In most cases:
define a TransactionManager in your XML
add this to your XML <tx:annotation-driven />
annotate your service method with #Transactional
You can find a sample setup in section Using #Transactional

Answer 2

Here is the solution:
i can not access the object on my web layer, i should access the lazy loading objects in service layer, which should be in a transaction.