使用POI读取word文档，读出下标越界

在网上下了POI包和tm-extractors-o.4.jar包，跟着网上的例子写了一个读word文档的程序，文档中只有几个字时能读出文档长度，加了一页后就报了以下异常，请各位帮帮忙，看看为什么会这样。谢谢
程序如下：
/*
 * Generated by MyEclipse Struts
 * Template path: templates/java/JavaClass.vtl
 */
package com.yourcompany.struts.action;import java.io.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.textmining.text.extraction.WordExtractor;
/** 
 * MyEclipse Struts
 * Creation date: 09-26-2010
 * 
 * XDoclet definition:
 * @struts.action validate="true"
 */
public class TowordAction extends Action {
/*
 * Generated Methods
 */ /** 
 * Method execute
 * @param mapping
 * @param form
 * @param request
 * @param response
 * @return ActionForward
 */
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
// TODO Auto-generated method stub
try{
FileInputStream in = new FileInputStream("d:\\aa.doc");
WordExtractor text = new WordExtractor();
String s = text.extractText(in);
System.out.print(s);
}catch(Exception e){
e.printStackTrace();
}
return null;
}
}
异常如下：
java.lang.StringIndexOutOfBoundsException: String index out of range: -1047
at java.lang.AbstractStringBuilder.substring(AbstractStringBuilder.java:881)
at java.lang.StringBuffer.substring(StringBuffer.java:416)
at org.apache.poi.hwpf.model.TextPiece.substring(TextPiece.java:88)
at org.textmining.text.extraction.WordExtractor.extractText(WordExtractor.java:179)
at com.yourcompany.struts.action.TowordAction.execute(TowordAction.java:42)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:743)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:284)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:204)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:750)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:510)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:359)
at org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:712)
at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:682)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:61)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:284)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:204)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:257)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:567)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:245)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:199)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:567)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:184)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:164)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:149)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:567)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:156)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:567)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:972)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:206)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:833)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:732)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:619)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:688)
at java.lang.Thread.run(Thread.java:619)