严重: Allocate exception for servlet aa

启动Tomcat出现以下异常

严重: Allocate exception for servlet aa
java.lang.ClassNotFoundException: cookie.aa
	at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1718)
	at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1569)
	at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:529)
	at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:511)
	at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:139)
	at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1143)
	at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:864)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:134)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

先说一下导致这个异常的原因，添加了两个servlet-api.jar包。

我是因为先是添加了这个包然后删除了tomcat再次添加一个新的tomcat再次添加了这个包导致出错了。

删除这个包的操作：

    右键工程Build Path->Config...，会出现以下图片。两个包都在我所画的框框里面，删除出错了的哪一个就好了。(我的已经删除了，出错的那个包下面会带有红叉)