DWR初次使用遇到的问题：Servlet dwr-invoker is not available

问题描述：Servlet dwr-invoker is not available

问题详细：

严重: Allocate exception for servlet dwr-invoker
java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory
at org.directwebremoting.servlet.DwrServlet.<clinit>(DwrServlet.java:180)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at java.lang.Class.newInstance0(Unknown Source)
at java.lang.Class.newInstance(Unknown Source)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1115)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:808)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:129)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)
2010-7-19 19:40:45 org.apache.catalina.core.StandardWrapperValve invoke
信息: Servlet dwr-invoker is currently unavailable
2010-7-19 19:40:49 org.apache.catalina.core.StandardWrapperValve invoke
信息: Servlet dwr-invoker is currently unavailable

解决方法：导入commons-logging.jar包即可