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)
解决方法：导入commons-logging.jar包即可
