这个又是什么原因
2011-9-27 12:42:26 org.apache.coyote.http11.Http11AprProtocol init
信息: Initializing Coyote HTTP/1.1 on http-8080
2011-9-27 12:42:26 org.apache.coyote.ajp.AjpAprProtocol init
信息: Initializing Coyote AJP/1.3 on ajp-8009
2011-9-27 12:42:26 org.apache.catalina.startup.Catalina load
信息: Initialization processed in 328 ms
2011-9-27 12:42:26 org.apache.catalina.core.StandardService start
信息: Starting service Catalina
2011-9-27 12:42:26 org.apache.catalina.core.StandardEngine start
信息: Starting Servlet Engine: Apache Tomcat/5.5.20
2011-9-27 12:42:26 org.apache.catalina.core.StandardHost start
信息: XML validation disabled
2011-9-27 12:42:26 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextInitialized()
2011-9-27 12:42:26 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextInitialized()
2011-9-27 12:42:26 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextInitialized()
2011-9-27 12:42:26 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextInitialized()
2011-9-27 12:42:26 org.apache.catalina.core.ApplicationContext log
信息: org.apache.webapp.balancer.BalancerFilter: init(): ruleChain: [org.apache.webapp.balancer.RuleChain: [org.apache.webapp.balancer.rules.URLStringMatchRule: Target string: News / Redirect URL: http://www.cnn.com], [org.apache.webapp.balancer.rules.RequestParameterRule: Target param name: paramName / Target param value: paramValue / Redirect URL: http://www.yahoo.com], [org.apache.webapp.balancer.rules.AcceptEverythingRule: Redirect URL: http://jakarta.apache.org]]
2011-9-27 12:42:30 org.apache.coyote.http11.Http11AprProtocol start
信息: Starting Coyote HTTP/1.1 on http-8080
2011-9-27 12:42:30 org.apache.coyote.ajp.AjpAprProtocol start
信息: Starting Coyote AJP/1.3 on ajp-8009
2011-9-27 12:42:30 org.apache.catalina.storeconfig.StoreLoader load
信息: Find registry server-registry.xml at classpath resource
2011-9-27 12:42:30 org.apache.catalina.startup.Catalina start
信息: Server startup in 4157 ms
[framework] 2011-09-27 12:42:53,906 - org.apache.struts.action.RequestProcessor -0 [http-8080-1] WARN org.apache.struts.action.RequestProcessor - Unhandled Exception thrown: class java.lang.NullPointerException
 [framework] 2011-09-27 12:42:53,906 - org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/log].[action] -0 [http-8080-1] ERROR org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/log].[action] - Servlet.service() for servlet action threw exception
 java.lang.NullPointerException
at com.hello.model.service.impl.UserService.isValidUser(UserService.java:15)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:304)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.aop.framework.Jdk