我正在将Spring Roo和Vaadin用于一个（简单的）数据库应用程序。有一个视图显示包含实体的表。对于要显示的表，Hibernate需要延迟加载1：n引用的实体。这适用于小型表，但是一旦表变大，就只能正确显示第一部分，并且会发生以下异常。
com.vaadin.data.util.MethodProperty$MethodException
at com.vaadin.data.util.MethodProperty.getValue(MethodProperty.java:612)
at com.vaadin.data.util.AbstractProperty.toString(AbstractProperty.java:78)
at com.vaadin.ui.Table.formatPropertyValue(Table.java:3476)
at eu.wuttke.tinyscrum.ui.dashboard.DashboardTaskStoryTable.formatPropertyValue(DashboardTaskStoryTable.java:66)
at com.vaadin.ui.Table.getPropertyValue(Table.java:3428)
at com.vaadin.ui.Table.getVisibleCellsNoCache(Table.java:1853)
at com.vaadin.ui.Table.refreshRenderedCells(Table.java:1477)
at com.vaadin.ui.Table.enableContentRefreshing(Table.java:2645)
at com.vaadin.ui.Table.changeVariables(Table.java:2491)
at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.changeVariables(AbstractCommunicationManager.java:1455)
at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.handleVariableBurst(AbstractCommunicationManager.java:1399)
at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.handleVariables(AbstractCommunicationManager.java:1318)
at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.doHandleUidlRequest(AbstractCommunicationManager.java:763)
at com.vaadin.terminal.gwt.server.CommunicationManager.handleUidlRequest(CommunicationManager.java:296)
at com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:501)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:147)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:291)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:769)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:698)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:891)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)
at java.lang.Thread.run(Thread.java:679)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor841.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at com.vaadin.data.util.MethodProperty.getValue(MethodProperty.java:610)
... 34 more
Caused by: org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:167)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:215)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:190)
at eu.wuttke.tinyscrum.domain.Iteration_$$_javassist_1.getName(Iteration_$$_javassist_1.java)
at eu.wuttke.tinyscrum.domain.Iteration_Roo_JavaBean.ajc$interMethodDispatch1$eu_wuttke_tinyscrum_domain_Iteration_Roo_JavaBean$eu_wuttke_tinyscrum_domain_Iteration$getName(Iteration_Roo_JavaBean.aj)
at eu.wuttke.tinyscrum.domain.TaskAndStory.getIterationName(TaskAndStory.java:32)
... 38 more
我从其他Hibernate应用程序知道此LazyInitializationException异常，该异常在会话未打开或已再次关闭时发生。但是，查看堆栈跟踪，似乎正在调用OpenEntityManagerInView过滤器。
有任何想法吗？非常感谢！
最佳答案
Vaadin在服务器端具有持久状态。如果您将对象绑定到Vaadin组件（例如，通过使用BeanItemContainer），则对象将“存在”多个服务器端的一个请求。
另一方面，Spring（通过OpenEntityManagerInView）将为每个请求（EntityManagers不安全）创建一个新的EntityManager，并在请求后关闭它。这样，您已经加载的Entities将变得分离（EM不再可用），并且当Vaadin向例如如果加载更多的表行，则延迟加载的fileds将无法加载（并且您将获得LazyInitializationException），因为加载它们的EM不再存在。
一些解决方案：
使用热切的JPA提取（@ManyToOne (fetch= FetchType.EAGER)）
使用JOIN FETCH查询（例如SELECT mag FROM Magazine mag LEFT JOIN FETCH mag.articles WHERE mag.id = 1 See more）加载对象
使用EclipseLink（EclipseLink将打开一个新的Session来为分离对象加载延迟加载字段）[我们正在使用这种方法]