关于HashMap遍历的问题

我在一个HashMap的遍历中，使用了四个以上不同的Iterator的next()方法，当程序执行到第四个next()的时候，开始抛出异常，如下：LinkedHashMap product = new LinkedHashMap();
LinkedHashMap order = new LinkedHashMap();
LinkedHashMap voucher = new LinkedHashMap();
LinkedHashMap quantity = new LinkedHashMap();
//以上hashmap我在实际中是经过数据库操作取得的，当前new仅为示例
Iterator pit = product.keySet().iterator();
Iterator oit = order.keySet().iterator();
Iterator vit = order.keySet().iterator();
Iterator qit = quantity.keySet().iterator();while(pit.hasNext()) {     String str_product = (String)pit.next();
     String str_order = (String)oit.next();
     String str_voucher = (String)vit.next();//当程序执行第四个next()时开始报出异常，如注释掉则可正常运行
     String str_qty = (String)qit.next();}
报出的异常如下：2008-12-10 9:43:18 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.IllegalStateException
at org.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java:435)
at org.apache.jsp._01309940orderquery_jsp._jspService(_01309940orderquery_jsp.java:503)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)请问在HashMap的遍历中，是不是不能使用多个不同Iterator的next()的方法?还是其它原因导致程序异常？非常感谢