LazyInitializationException（Spring和Vaadin）儘管OpenEntityManagerInView

Question

我正在使用Spring Roo和Vaadin來創建（簡單）數據庫應用程序。有一個視圖顯示一個包含實體的表。對於要顯示的表，Hibernate需要延遲加載1：n引用的實體。這適用於小型表格，但只要表格變大，只有第一部分顯示正確，並且會發生以下異常。

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 

我知道，從其他的Hibernate應用此LazyInitializationException中例外，在那裏當會話未打開或者已經關閉再次發生。但看着堆棧跟蹤，看起來OpenEntityManagerInView過濾器正在被調用。

任何想法？非常感謝！

Answer 1

Vaadin在服務器端有一個持久狀態。如果您將對象綁定到Vaadin組件（例如，通過使用BeanItemContainer），則您的對象將在服務器端「活動」多個請求。

另一方面，Spring（通過OpenEntityManagerInView）將爲每個請求創建一個新的EntityManager（EntityManagers不是安全的），並在請求後關閉它。這樣，你已經加載的Entities將會變得分離（EM不再可用），並且當Vaadin提出新的請求時，例如，加載更多的錶行，懶加載文件將無法加載（你將得到LazyInitializationException），因爲加載它們的EM不再存在。

一些解決方案：

• 使用你反對的渴望JPA獲取（@ManyToOne (fetch= FetchType.EAGER)）
• 負載連接抓取查詢（例如SELECT mag FROM Magazine mag LEFT JOIN FETCH mag.articles WHERE mag.id = 1See more）
• 將EclipseLink（的EclipseLink將打開一個新的會話負載分離對象的延遲加載字段）[我們正在使用這種方法]