【发布时间】：2014-05-14 10:14:25
【问题描述】：
我正在从 Myfaces 1.2 升级到 Myfaces 2.2。
我遇到了一个问题，当 bean 的值由于 bean 的重新初始化而丢失时。所以我尝试将 bean 的范围从请求范围更改为查看范围，但我遇到了错误。
控制台错误：-
java.lang.NullPointerException
at org.apache.myfaces.el.unified.resolver.ManagedBeanResolver$5.put(ManagedBeanResolver.java:101) [myfaces-impl-2.2.2.jar]
at org.apache.myfaces.el.unified.resolver.ManagedBeanResolver.putInScope(ManagedBeanResolver.java:367) [myfaces-impl-2.2.2.jar]
at org.apache.myfaces.el.unified.resolver.ManagedBeanResolver.createManagedBean(ManagedBeanResolver.java:340) [myfaces-impl-2.2.2.jar]
at org.apache.myfaces.el.unified.resolver.ManagedBeanResolver.getValue(ManagedBeanResolver.java:296) [myfaces-impl-2.2.2.jar]
at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67) [el-api.jar:2.2.FR]
at org.apache.myfaces.el.unified.resolver.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:179) [myfaces-impl-2.2.2.jar]
at org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:72) [jasper-el.jar:7.0.39]
at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185) [jasper-el.jar:7.0.39]
at org.apache.myfaces.lifecycle.PhaseListenerManager.informPhaseListenersBefore(PhaseListenerManager.java:77) [myfaces-impl-2.2.2.jar]
at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:184) [myfaces-impl-2.2.2.jar]
at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:143) [myfaces-impl-2.2.2.jar]
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:198) [myfaces-api-2.2.2.jar]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) [catalina.jar:7.0.39]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39]
at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:349) [tomahawk20-1.1.10.jar]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) [catalina.jar:7.0.39]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) [catalina.jar:7.0.39]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) [catalina.jar:7.0.39]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) [catalina.jar:7.0.39]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) [catalina.jar:7.0.39]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) [catalina.jar:7.0.39]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) [catalina.jar:7.0.39]
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:947) [catalina.jar:7.0.39]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) [catalina.jar:7.0.39]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) [catalina.jar:7.0.39]
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1009) [tomcat-coyote.jar:7.0.39]
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) [tomcat-coyote.jar:7.0.39]
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) [tomcat-coyote.jar:7.0.39]
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [1.6.0_35]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [1.6.0_35]
at java.lang.Thread.run(Thread.java:662) [1.6.0_35]
【问题讨论】：
-
看起来您正试图在创建视图之前访问视图范围 bean，这是无效的。从请求更改为查看范围将无济于事。你需要用其他方式解决原来的问题。
-
当我在请求范围内使用 JSF 1.2 时，应用程序之前运行良好。只是在升级之后，我开始遇到问题，然后我更改为查看范围。
-
查看范围与请求范围不同，因此您不应该进行这种更改。
-
我知道它们不一样，但随着 bean 值丢失，我尝试增加查看范围。
-
您应该使用一个 bean 来存储视图范围中的值，而另一个 bean 来处理请求范围逻辑，在这种情况下绑定到阶段侦听器方法。这样它就可以工作了。