dwr运行时出现Servlet.init() for servlet dwr

错误信息如下:

javax.servlet.ServletException: Servlet.init() for servlet dwr-invoker threw exception

org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)

org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)

org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)

org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)

org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)

java.lang.Thread.run(Unknown Source)

root cause

java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory

org.directwebremoting.dwrp.PollHandler.<clinit>(PollHandler.java:382)

java.lang.Class.forName0(Native Method)

java.lang.Class.forName(Unknown Source)

org.directwebremoting.impl.ContainerUtil.class$(ContainerUtil.java:97)

org.directwebremoting.impl.ContainerUtil.setupDefaults(ContainerUtil.java:150)

org.directwebremoting.impl.ContainerUtil.setupDefaultContainer(ContainerUtil.java:125)

org.directwebremoting.servlet.DwrServlet.init(DwrServlet.java:73)

org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)

org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)

org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)

org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)

org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)

java.lang.Thread.run(Unknown Source)

root cause

java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory

org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1360)

org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1206)

java.lang.ClassLoader.loadClassInternal(Unknown Source)