我正在尝试使用网络服务。我的客户端作为托管在 Tomcat 上的 JSP 页面运行。在尝试使用该服务时，我收到此错误：
HTTP Status 500 - Unexpected error: null
我知道这个问题出在服务器端。我正在使用 RPC 样式的 SOAP 请求。我是 JAVA 和 Web 服务的新手，所以我需要一种方法来找到错误的变量。我该如何解决这个问题？
type Exception report
message Unexpected error: null
description The server encountered an internal error that prevented it from fulfilling this request.
exception
Unexpected error: null
org.apache.axis.message.SOAPFaultBuilder.createFault(SOAPFaultBuilder.java:222)
org.apache.axis.message.SOAPFaultBuilder.endElement(SOAPFaultBuilder.java:129)
org.apache.axis.encoding.DeserializationContext.endElement(DeserializationContext.java:1087)
com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(Unknown Source)
com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source)
com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source)
com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(Unknown Source)
com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source)
com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl.parse(Unknown Source)
org.apache.axis.encoding.DeserializationContext.parse(DeserializationContext.java:227)
org.apache.axis.SOAPPart.getAsSOAPEnvelope(SOAPPart.java:696)
org.apache.axis.Message.getSOAPEnvelope(Message.java:435)
org.apache.axis.handlers.soap.MustUnderstandChecker.invoke(MustUnderstandChecker.java:62)
org.apache.axis.client.AxisClient.invoke(AxisClient.java:206)
org.apache.axis.client.Call.invokeEngine(Call.java:2784)
org.apache.axis.client.Call.invoke(Call.java:2767)
org.apache.axis.client.Call.invoke(Call.java:2443)
org.apache.axis.client.Call.invoke(Call.java:2366)
org.apache.axis.client.Call.invoke(Call.java:1812)
com.xxxx.xxxx.xxxx.xxxx.Ouxxxxxxx._xxxx.OutagexxxxxxxStub.newOutageRequest(OxxxxxxxxxxxngStub.java:1986)
com.xxxx.xxxx.xxxx.xxxx.Outxxxxxxxrvice._xxxx.OutxxxxxxxxxxiceProxy.newOutageRequest(Oxxxxxxxxy.java:158)
com.xxxx.xxxxxxxxxx.doPost(SubmxxxxID.java:178)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)