SpringBoot启动项目报错： Cannot expose session attribute 'user' because of an existing model object of the_javax.servlet.servletexception: cannot expose sess-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_40615403/article/details/88124205

在使用SpringBoot和Freemarker时遇到报错：Cannot expose session attribute 'user' due to an existing model object. 解决方案是通过配置Freemarker，设置`expose-session-attributes: true`并启用`allow-session-override: true`来允许session属性被重写，从而解决session冲突问题。

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报错：Cannot expose session attribute 'user' because of an existing model object of the same name

javax.servlet.ServletException: Cannot expose session attribute 'user' because of an existing model object of the same name
	at org.springframework.web.servlet.view.AbstractTemplateView.renderMergedOutputModel(AbstractTemplateView.java:141) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1286) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1041) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:984) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:687) ~[javax.servlet-api-3.1.0.jar:3.1.0]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) ~[javax.servlet-api-3.1.0.jar:3.1.0]
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:848) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1772) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.websocket.server.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:205) ~[websocket-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55) ~[spring-boot-1.4.7.RELEASE.jar:1.4.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at com.mooc.house.web.filter.LogFilter.doFilter(LogFilter.java:28) ~[classes/:?]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:105) ~[spring-boot-actuator-1.4.7.RELEASE.jar:1.4.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:105) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:106) ~[spring-boot-actuator-1.4.7.RELEASE.jar:1.4.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.9.RELEASE.jar:4.3.9.RELEASE]
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) ~[jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:582) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548) [jetty-security-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1180) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:512) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1112) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.Server.handle(Server.java:534) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:320) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:251) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:283) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:108) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502]
	at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]

这个问题是session重复，解决方法就是session重写.

freemarker:
    charset: UTF-8
    content-type: text/html; charset=utf-8
    expose-request-attributes: true
    expose-session-attributes: true      #将session的属性暴露出来给后台
    expose-spring-macro-helpers: true    #暴露freemarker的宏定义
    suffix: .ftl    #设置freemarker的后缀
    allow-session-override : true   #设置允许session被重写