我已经在debian系统上得到java，tomcat6，并得到这个exception。 我该如何解决？

root@konrad:/var/lib/tomcat6/logs# cat localhost.2012-07-12.log Jul 12, 2012 9:26:30 AM org.apache.catalina.core.StandardContext filterStart SEVERE: Exception starting filter SetCharacterEncoding java.lang.ClassNotFoundException: org.apache.catalina.filters.SetCharacterEncodingFilter at java.net.URLClassLoader$1.run(URLClassLoader.java:217) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:205) at java.lang.ClassLoader.loadClass(ClassLoader.java:321) at java.lang.ClassLoader.loadClass(ClassLoader.java:266) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:269) at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:422) at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:115) at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4072) at org.apache.catalina.core.StandardContext.start(StandardContext.java:4726) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:799) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:779) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:601) at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:675) at org.apache.catalina.startup.HostConfig.deployDescriptors(HostConfig.java:601) at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:502) at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1317) at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:324) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:142) at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1065) at org.apache.catalina.core.StandardHost.start(StandardHost.java:840) at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057) at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:463) at org.apache.catalina.core.StandardService.start(StandardService.java:525) at org.apache.catalina.core.StandardServer.start(StandardServer.java:754) at org.apache.catalina.startup.Catalina.start(Catalina.java:595) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)