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。
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需求进行初始化。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：
employee
lazy
Query empQuery = session.createQuery(hqlQuery); empQuery.setMaxResults(maxResult); employees = (List<Employee>) empQuery.list(); for (Employee emp : employees) { Hibernate.initialize(emp.address); }
