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[学习交流] 【上海校区】SSS框架整合no session（延迟加载）问题分析及...

© 不二晨 金牌黑马   /  2018-7-11 09:20  /  869 人查看  /  3 人回复  /   0 人收藏 转载请遵从CC协议 禁止商业使用本文

问题描述：

        在做BOS物流管理系统的时候，点击区域页面显示配送区域信息，这个时候后台显示了no session的错误



  • org.apache.struts2.json.JSONException: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.itheima.domain.Area.subareas, could not initialize proxy - no Session



  •         at org.apache.struts2.json.JSONWriter.bean(JSONWriter.java:246)



  •         at org.apache.struts2.json.JSONWriter.processCustom(JSONWriter.java:178)



  •         at org.apache.struts2.json.JSONWriter.process(JSONWriter.java:168)



  •         at org.apache.struts2.json.JSONWriter.value(JSONWriter.java:134)



  •         at org.apache.struts2.json.JSONWriter.array(JSONWriter.java:492)



  •         at org.apache.struts2.json.JSONWriter.process(JSONWriter.java:158)



  •         at org.apache.struts2.json.JSONWriter.value(JSONWriter.java:134)



  •         at org.apache.struts2.json.JSONWriter.map(JSONWriter.java:447)



  •         at org.apache.struts2.json.JSONWriter.process(JSONWriter.java:154)



  •         at org.apache.struts2.json.JSONWriter.value(JSONWriter.java:134)



  •         at org.apache.struts2.json.JSONWriter.write(JSONWriter.java:102)



  •         at org.apache.struts2.json.JSONUtil.serialize(JSONUtil.java:107)



  •         at org.apache.struts2.json.JSONResult.createJSONString(JSONResult.java:203)



  •         at org.apache.struts2.json.JSONResult.execute(JSONResult.java:177)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:369)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:273)



  •         at org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)



  •         at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)



  •         at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:76)



  •         at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)



  •         at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)



  •         at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept(DateTextFieldInterceptor.java:125)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:253)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)



  •         at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)



  •         at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)



  •         at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)



  •         at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)



  •         at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)



  •         at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)



  •         at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)



  •         at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)



  •         at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)



  •         at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)



  •         at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)



  •         at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)



  •         at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)



  •         at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)



  •         at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)



  •         at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)



  •         at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)



  •         at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)



  •         at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)



  •         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)



  •         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)



  •         at java.lang.Thread.run(Thread.java:748)



  • Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.itheima.domain.Area.subareas, could not initialize proxy - no Session



  •         at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:563)



  •         at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:205)



  •         at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:542)



  •         at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:133)



  •         at org.hibernate.collection.internal.PersistentSet.equals(PersistentSet.java:423)



  •         at java.util.Vector.indexOf(Vector.java:411)



  •         at java.util.Vector.contains(Vector.java:370)



  •         at org.apache.struts2.json.JSONWriter.value(JSONWriter.java:117)



  •         at org.apache.struts2.json.JSONWriter.add(JSONWriter.java:401)



  •         at org.apache.struts2.json.JSONWriter.bean(JSONWriter.java:231)



  •         ... 81 more


看系统提示可以看出来是因为加载Area类中的subareas属性出现了问题。我们再来看下Area类中有哪些属性



  •         @Id



  •         @Column(name = "C_ID")



  •         private String id;



  •         @Column(name = "C_PROVINCE")



  •         private String province; // 省



  •         @Column(name = "C_CITY")



  •         private String city; // 城市



  •         @Column(name = "C_DISTRICT")



  •         private String district; // 区域



  •         @Column(name = "C_POSTCODE")



  •         private String postcode; // 邮编



  •         @Column(name = "C_CITYCODE")



  •         private String citycode; // 城市编码



  •         @Column(name = "C_SHORTCODE")



  •         private String shortcode; // 简码







  •         @OneToMany(mappedBy = "area")



  •         private Set<SubArea> subareas = new HashSet<SubArea>();


        为什么Area中这么多属性，只有subareas属性出现了问题？可以看出来这里的subareas是一个集合，问题就出现在这里，在spring框架中集合属性的查询默认的是懒加载的，也就是说在service层调用dao层的查询方法时，dao层并不会向数据库发送查询语句，而是将查询语句藏在了session的一级缓存区域，在下一次subareas被使用到的时候才会真正向数据区发送查询语句，这样的好处是可以为系统节省资源，但是同样也带来一个问题，因为我们第一次调用subareas是在web层将查询到的数据打包成json数据的时候，但是我们的session在service层就已经被关闭了，我们都知道sss框架和ssh框架的底层都是Hibernate中的session对象对数据库进行操作的。因此就会出现no session的异常。

问题解决：第一种：让session存活到web层

    添加OpenEntityManagerInViewFilter过滤器（必须配置在struts拦截器前）,原理就是将session的创建和关闭放在过滤器中，这样就可以让session存活到web层。

第二种：立即加载（不建议）

        立即加载就是消除懒加载，运用JPA注解的属性fetch=FetchType.EAGER




  •         @OneToMany(mappedBy = "area",fetch=FetchType.EAGER)



  •         private Set<SubArea> subareas = new HashSet<SubArea>();


      这样就可以在dao层立即加载subareas，这样在web层就可以直接使用到subareas的数据了。

第三种：取消序列化

        如果subareas这个属性并不是需要的数据的话，可以通过注解让json在序列化Area的属性的时候，跳过subareas这个属性。这样就不需要向数据库查询subareas的数据了，也就不会出现懒加载的问题了。

【转载】原文地址：https://blog.csdn.net/GechangLiu/article/details/80994568


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