怎么样在一个已存在的Web应用中利用Axis2发布服务

都导入了，web.xml中配置了AxisServlet，lib中也把axis2.war中的所有jar都导入了，但是还是会报一个错：
escription The server encountered an internal error () that prevented it from fulfilling this request.exceptionjavax.servlet.ServletException
org.apache.axis2.transport.http.AxisServlet.init(AxisServlet.java:334)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:307)
org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:385)
org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:748)
org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:678)
org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:871)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
java.lang.Thread.run(Thread.java:534)root causejavax.servlet.ServletException
org.apache.axis2.transport.http.AxisServlet.initConfigContext(AxisServlet.java:378)
org.apache.axis2.transport.http.AxisServlet.init(AxisServlet.java:317)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:307)
org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:385)
org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:748)
org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:678)
org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:871)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
java.lang.Thread.run(Thread.java:534)root causejava.lang.NullPointerException
org.apache.axis2.deployment.DeploymentEngine.loadServices(DeploymentEngine.java:88)
org.apache.axis2.deployment.WarBasedAxisConfigurator.loadServices(WarBasedAxisConfigurator.java:239)
org.apache.axis2.context.ConfigurationContextFactory.createConfigurationContext(ConfigurationContextFactory.java:72)
org.apache.axis2.transport.http.AxisServlet.initConfigContext(AxisServlet.java:373)
org.apache.axis2.transport.http.AxisServlet.init(AxisServlet.java:317)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:307)
org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:385)
org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:748)
org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:678)
org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:871)
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
java.lang.Thread.run(Thread.java:534)note The full stack trace of the root cause is available in the Apache Tomcat/5.5.9 logs.