Tomcat 7.0在运行中出现下列错误提示，请问是什么原因？网站可以正常发布，但是控制台会出现下面的错误

错误代码如下：

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信息: Illegal access: this web application instance has been stopped already. Could not load org.apache.commons.pool2.impl.LinkedBlockingDeque$Node. The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.

java.lang.IllegalStateException

at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1610)

at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1569)

at org.apache.commons.pool2.impl.LinkedBlockingDeque.linkFirst(LinkedBlockingDeque.java:248)

at org.apache.commons.pool2.impl.LinkedBlockingDeque.offerFirst(LinkedBlockingDeque.java:393)

at org.apache.commons.pool2.impl.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:368)

at org.apache.commons.pool2.impl.GenericObjectPool.ensureIdle(GenericObjectPool.java:927)

at org.apache.commons.pool2.impl.GenericObjectPool.ensureMinIdle(GenericObjectPool.java:899)

at org.apache.commons.pool2.impl.BaseGenericObjectPool$Evictor.run(BaseGenericObjectPool.java:1036)

at java.util.TimerThread.mainLoop(Unknown Source)

at java.util.TimerThread.run(Unknown Source)

Exception in thread "commons-pool-EvictionTimer" java.lang.NoClassDefFoundError: org/apache/commons/pool2/impl/LinkedBlockingDeque$Node

at org.apache.commons.pool2.impl.LinkedBlockingDeque.linkFirst(LinkedBlockingDeque.java:248)

at org.apache.commons.pool2.impl.LinkedBlockingDeque.offerFirst(LinkedBlockingDeque.java:393)

at org.apache.commons.pool2.impl.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:368)

at org.apache.commons.pool2.impl.GenericObjectPool.ensureIdle(GenericObjectPool.java:927)

at org.apache.commons.pool2.impl.GenericObjectPool.ensureMinIdle(GenericObjectPool.java:899)

at org.apache.commons.pool2.impl.BaseGenericObjectPool$Evictor.run(BaseGenericObjectPool.java:1036)

at java.util.TimerThread.mainLoop(Unknown Source)

at java.util.TimerThread.run(Unknown Source)

Caused by: java.lang.ClassNotFoundException: org.apache.commons.pool2.impl.LinkedBlockingDeque$Node

at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1718)

at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1569)

... 8 more

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