史无前例tomcat6 怪问题 ?报错

在web.xml 添加一个servlet：

<servlet>
  <servlet-name>coreServlet</servlet-name>
  <servlet-class>com.TestServlet</servlet-class>
 </servlet>
 <servlet-mapping>
   <servlet-name>coreServlet</servlet-name>
   <url-pattern>/coreServlet</url-pattern>
 </servlet-mapping>

二、之前访问一直是正常的，然后过一会访问就报错：

exception

javax.servlet.ServletException: Error instantiating servlet class com.TestServlet org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
	org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
	org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
	org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	java.lang.Thread.run(Thread.java:662)

root cause

javax.naming.NameNotFoundException: Name com.TestServlet is not bound in this Context
	org.apache.naming.NamingContext.lookup(NamingContext.java:770)
	org.apache.naming.NamingContext.lookup(NamingContext.java:153)
	org.apache.catalina.util.DefaultAnnotationProcessor.lookupFieldResource(DefaultAnnotationProcessor.java:278)
	org.apache.catalina.util.DefaultAnnotationProcessor.processAnnotations(DefaultAnnotationProcessor.java:187)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
	org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
	org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
	org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	java.lang.Thread.run(Thread.java:662)