System.out.println() 在 Java 中有副作用吗？答案

【问题标题】：Does System.out.println() have a side effect in Java?System.out.println() 在 Java 中有副作用吗？
【发布时间】：2023-03-27 12:07:01
【问题描述】：

当我将 println() 放在 DAO 方法中时，当我调用 update 方法时，程序就会工作。

@Override
public Post getPostById(int id) {
    Session session = DatabaseConnection.connect().openSession();
    Post post = (Post) session.load(Post.class, new Integer(id));
    System.out.println("debug " + post);
    session.close();
    return post;
}

如果我不这样做，它会给我一个错误

@Override
public Post getPostById(int id) {
    Session session = DatabaseConnection.connect().openSession();
    Post post = (Post) session.load(Post.class, new Integer(id));

    session.close();
    return post;
}

这是错误消息：

   SEVERE: Invalid property 'account' of bean class [com.personal.pojo.Post_$$_jvsta3d_0]: Getter for property 'account' threw exception; nested exception is java.lang.reflect.InvocationTargetException
org.springframework.beans.InvalidPropertyException: Invalid property 'account' of bean class [com.personal.pojo.Post_$$_jvsta3d_0]: Getter for property 'account' threw exception; nested exception is java.lang.reflect.InvocationTargetException
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:704)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getNestedPropertyAccessor(AbstractNestablePropertyAccessor.java:836)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyAccessorForPropertyPath(AbstractNestablePropertyAccessor.java:813)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:608)
    at org.springframework.validation.AbstractPropertyBindingResult.getActualFieldValue(AbstractPropertyBindingResult.java:99)
    at org.springframework.validation.AbstractBindingResult.getFieldValue(AbstractBindingResult.java:229)
    at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:120)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:168)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:188)
    at org.springframework.web.servlet.tags.form.LabelTag.autogenerateFor(LabelTag.java:130)
    at org.springframework.web.servlet.tags.form.LabelTag.resolveFor(LabelTag.java:120)
    at org.springframework.web.servlet.tags.form.LabelTag.writeTagContent(LabelTag.java:90)
    at org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:84)
    at org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
    at org.apache.jsp.WEB_002dINF.jsp.edit_jsp._jspx_meth_form_005flabel_005f0(edit_jsp.java:278)
    at org.apache.jsp.WEB_002dINF.jsp.edit_jsp._jspx_meth_form_005fform_005f0(edit_jsp.java:193)
    at org.apache.jsp.WEB_002dINF.jsp.edit_jsp._jspService(edit_jsp.java:144)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:719)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:465)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:390)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:317)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1243)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:169)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.beans.BeanWrapperImpl$BeanPropertyHandler.getValue(BeanWrapperImpl.java:307)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:622)
    ... 95 more
Caused by: org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    at com.personal.pojo.Post_$$_jvsta3d_0.getAccount(Post_$$_jvsta3d_0.java)
    ... 101 more

Dec 31, 2015 7:03:28 PM org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet jsp threw exception
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    at com.personal.pojo.Post_$$_jvsta3d_0.getAccount(Post_$$_jvsta3d_0.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 org.springframework.beans.BeanWrapperImpl$BeanPropertyHandler.getValue(BeanWrapperImpl.java:307)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:622)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getNestedPropertyAccessor(AbstractNestablePropertyAccessor.java:836)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyAccessorForPropertyPath(AbstractNestablePropertyAccessor.java:813)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:608)
    at org.springframework.validation.AbstractPropertyBindingResult.getActualFieldValue(AbstractPropertyBindingResult.java:99)
    at org.springframework.validation.AbstractBindingResult.getFieldValue(AbstractBindingResult.java:229)
    at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:120)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:168)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:188)
    at org.springframework.web.servlet.tags.form.LabelTag.autogenerateFor(LabelTag.java:130)
    at org.springframework.web.servlet.tags.form.LabelTag.resolveFor(LabelTag.java:120)
    at org.springframework.web.servlet.tags.form.LabelTag.writeTagContent(LabelTag.java:90)
    at org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:84)
    at org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
    at org.apache.jsp.WEB_002dINF.jsp.edit_jsp._jspx_meth_form_005flabel_005f0(edit_jsp.java:278)
    at org.apache.jsp.WEB_002dINF.jsp.edit_jsp._jspx_meth_form_005fform_005f0(edit_jsp.java:193)
    at org.apache.jsp.WEB_002dINF.jsp.edit_jsp._jspService(edit_jsp.java:144)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:719)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:465)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:390)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:317)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1243)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:169)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

这是我调用的方法：

@RequestMapping("/edit/{id}")
public String editPost(@PathVariable("id") int id, Model model)
{
    model.addAttribute("post", RegistryDAO.getPostDAO().getPostById(id));
    return "edit";
}

这怎么可能？

【问题讨论】：

问题出在生成的 getter 上，如果没有 COMPLETE 堆栈跟踪显示导致 InvocationTargetException 的原因，则无法进一步排除故障。
潜在重复：stackoverflow.com/questions/21574236/…stackoverflow.com/questions/14542140/…stackoverflow.com/questions/19361963/…stackoverflow.com/q/7654818/18157
请发布您的edit.jsp内容和com.personal.pojo.Post的完整来源。显然，您的 JSP 正在尝试显示它无法在 Post 中访问的字段（帐户）。
System.out.println 中使用的连接运算符可能会产生副作用。这将导致post.toString() 被调用；通常，这样的方法不应该有影响其他任何东西的副作用，但取决于它的编码方式，它可以。对此进行测试的一种方法是使用System.out.println("debug") 并查看错误是否仍然存在。

标签： java spring

【解决方案1】：

System.out.println() 在 Java 中有副作用吗？

是的。一个副作用是它会产生输出！

但更重要的是（在您的情况下）它可以改变时间和线程调度。如果您的代码中的其他地方存在并发错误，则 println 可以防止该错误发生。

错误信息不是很丰富，但似乎是说某些对象（bean）具有account 属性，并且getter 失败了。如果您可以获得完整的异常堆栈跟踪（例如从日志文件中），那么那里应该有更多线索。

这是根异常消息（来自您添加的堆栈跟踪）：

Caused by: org.hibernate.LazyInitializationException: 
    could not initialize proxy - no Session

Jim Garrison 根据该消息确定了许多可能的重复项；见上面的评论。先检查那些。

可能是那个 session.close(); getPostById 内部过早关闭会话？

是的，它可能是。您需要在处理（打开和关闭）会话的方式上保持一致。

请注意，如果您“缓存”使用短期Session 创建的对象，那么当Session 关闭时它们会断开连接。如果对象被延迟初始化，这可能会导致问题。我找到了这个解释（在Altassian documentation）：

休眠会话

会话是一种 Hibernate 构造，用于调解与数据库的连接。

会话在创建时打开单个数据库连接，并一直保持到会话关闭。 Hibernate 从数据库中加载的每个对象都与会话相关联，允许 Hibernate 自动持久化被修改的对象，并允许 Hibernate 实现延迟加载等功能。

断开的对象

如果一个对象从其会话中被逐出（例如通过清除，见下文），或者会话在对象仍保持活动状态时关闭，则该对象与会话“断开连接”。只要您不执行任何需要返回数据库的操作（例如访问延迟加载的集合），断开连接的对象将继续工作。

如果您看到 LazyInitializationException，这意味着 Hibernate 管理的对象的寿命比它的会话长。

托管对象在会话之间不可移植。尝试在一个会话中加载对象然后将其保存到另一个会话中也会导致错误。（您可以使用 Session.load() 或 Session.get() 将对象重新引入新会话，但最好先解决导致您尝试在会话之间移动对象的任何问题.

【讨论】：

会不会是那个 session.close(); getPostById 内部过早关闭会话？
我不知道，为什么你会称它为“过早”。当调用session.close() 时，会话关闭。因此，如果您不想这样做，请删除该方法调用。
嗯，对，但我应该让它保持打开状态，还是有比这更好的解决方案？