休眠：org.hibernate.LazyInitializationException：无法初始化代理-没有会话

Question

对数据库有以下查询：

        Session session = EmployeesDAO.getSessionFactory().getCurrentSession();
        List<Employee> employees = new ArrayList<Employee>();
        try {
            session.beginTransaction();
            String hqlQuery = "from Employee emp "
                    + "left join fetch emp.employeesOffices employeesOffice "
                    + "left join fetch employeesOffice.office employeesOfficeOffice "
                    + "left join fetch employeesOfficeOffice.company "
                    + "left join fetch emp.address empAddress "
                    + "left join fetch empAddress.city empAddressCity "
                    + "left join fetch empAddressCity.country";
            Query empQuery = session.createQuery(hqlQuery);
            empQuery.setMaxResults(maxResult);
            employees = (List<Employee>) empQuery.list();
            session.getTransaction().commit();

        } catch (HibernateException e) {
            session.getTransaction().rollback();
            e.printStackTrace();
        }

在获取employee.address.street，employee.address.houseNumber或employee.address.city时，它将失败，但以下情况除外：

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:164)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    at com.employees.model.Address_$$_javassist_6.getCity(Address_$$_javassist_6.java)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:87)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:169)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:985)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspx_meth_c_005fout_005f3(listEmployees_jsp.java:306)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspx_meth_c_005fforEach_005f1(listEmployees_jsp.java:248)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspx_meth_c_005fforEach_005f0(listEmployees_jsp.java:155)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspService(listEmployees_jsp.java:89)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:690)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:477)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:402)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
    at com.employees.controller.EmployeeController.processRequest(EmployeeController.java:69)
    at com.employees.controller.EmployeeController.doGet(EmployeeController.java:30)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

员工映射：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.employees.model.Employee" table="employees">
        <id column="employee_id" name="employeeId" type="int">
            <generator class="sequence">
                <param name="sequence">EMP_SEQ</param>
            </generator>
        </id>
        <property column="first_name" name="firstName" type="java.lang.String" />
        <property column="last_name" name="lastName" type="java.lang.String" />

        <many-to-one name="address" column="address_id" 
            class="com.employees.model.Address"/>
        <set name="employeesOffices" >
            <key column="employee_id" />
            <one-to-many class="com.employees.model.EmployeeOffice"/>
        </set>

    </class>
</hibernate-mapping>

地址映射：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.employees.model.Address" table="addresses">
        <id column="address_id" name="addressId" type="int">
            <generator class="sequence">
                <param name="sequence">ADDRESS_SEQ</param>
            </generator>
        </id>
        <property column="street" name="street" type="java.lang.String" />
        <property column="house_number" name="houseNumber" type="int" />
        <many-to-one name="city" column="city_id"
            class="com.employees.model.City"/>
    </class>

</hibernate-mapping>

对于其他类（办公室，公司等），这​​是绝对正常的。如果注释，则在jsp应用程序中加载地址字段的行将正常工作。怎么了？顺便说一下，尽管有异常，它仍显示有关jsp的所有信息。

Answer 1

您内部employee的对象已lazy初始化。这意味着，它们仅根据非封闭会话的要求进行初始化。因此，在从数据库中获取数据后，您必须在循环内手动初始化它们：

Query empQuery = session.createQuery(hqlQuery);
empQuery.setMaxResults(maxResult);
employees = (List<Employee>) empQuery.list();
for (Employee emp : employees) {
    Hibernate.initialize(emp.address);
}