java.lang.NoClassDefFoundError:com/couchbase/client/CouchbaseClient

上个基于MSM配置tomcat session共享集群实验http://blog.chinaunix.net/uid-30212356-id-5727916.html时，在配置好一切后启动tomcat服务时无法启动，查看了错误日志catalina.out后发现了一处错误造成tomcat无法启动：
SEVERE: Begin event threw error
java.lang.NoClassDefFoundError: com/couchbase/client/CouchbaseClient
        at de.javakaffee.web.msm.MemcachedBackupSessionManager.(MemcachedBackupSessionManager.java:80)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
        at java.lang.Class.newInstance(Class.java:442)
        at org.apache.tomcat.util.digester.ObjectCreateRule.begin(ObjectCreateRule.java:145)
        at org.apache.tomcat.util.digester.Digester.startElement(Digester.java:1282)
        at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:509)
        at com.sun.org.apache.xerces.internal.parsers.AbstractXMLDocumentParser.emptyElement(AbstractXMLDocumentParser.java:182)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(XMLDocumentFragmentScannerImpl.java:1344)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2787)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
        at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848)
        at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777)
        at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
        at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
        at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
        at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1555)
        at org.apache.catalina.startup.Catalina.load(Catalina.java:616)
        at org.apache.catalina.startup.Catalina.load(Catalina.java:667)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.apache.catalina.startup.Bootstrap.load(Bootstrap.java:253)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:427)
Caused by: java.lang.ClassNotFoundException: com.couchbase.client.CouchbaseClient
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 28 more

原因：msm1.6.5依赖了Couchbase，需要添加couchbase-client的jar包，否则启动会报java.lang.NoClassDefFoundError:com/couchbase/client/CouchbaseClient错误；

解决办法：下载名为couchbase-client的jar包放到各tomcat的$CATALINA_HOME/lib下即可；
  
下载地址：   

或者这里：



解决问题参考的文章：