[求助]webservice调用出错

呀.我也遇到这个问题呀.真的好郁闷,,空指针..查了N久也不知道出在什么原因.
测试2007-09-21
测试2007-09-LoginName=mok
测试2007-09-Password=123
测试2007-09-21ssssssssss
java.lang.NullPointerException
        at com.webservice.OnLineExamClient.getExamList(OnLineExamClient.java:40)        at com.struts.action.ExamAction.getExamList(ExamAction.java:97)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchActio
n.java:274)
        at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:
194)
        at org.apache.struts.action.RequestProcessor.processActionPerform(Reques
tProcessor.java:419)
        at org.apache.struts.action.RequestProcessor.process(RequestProcessor.ja
va:224)
        at org.apache.struts.action.ActionServlet.process(ActionServlet.java:119
4)
        at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl
icationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF
ilterChain.java:173)
        at com.util.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilt
er.java:74)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl
icationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF
ilterChain.java:173)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperV
alve.java:213)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextV
alve.java:178)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.j
ava:126)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.j
ava:105)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineVal
ve.java:107)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.jav
a:148)
        at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcesso
r.java:833)
        at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.pr
ocess(Http11AprProtocol.java:639)
        at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:12
85)
        at java.lang.Thread.run(Unknown Source)