各位大大，JSP初学者求助……

各位大大好！
我现在正在学JSP，这个JSP是教程上面的例子，但是我把它打下来准备在我自己建的tomcat服务器上运行就是报错，貌似服务器和JSP配置应该是没有错的……程序功能就是点击按钮，选择将当前页面保存为一个Word 文挡时，
JSP 页面动态地改变contentType的属性值为application/msword。这时，客户的浏览器
会提示客户用Ms-Word 格式来显示当前页面
JSP文件如下：
<%@ page contentType="text/html;charset=GB2312" %>
<HTML>
<BODY bgcolor=cyan><Font size=1 >
<P> 我正在学习response 对象的
<BR>setContentType 方法
<P> 将当前页面保存为word 文档吗？
<FORM action="" method="get" name=form>
<INPUT TYPE="submit" value="yes" name="submit">
</FORM>
<% String str=request.getParameter("submit");
if(str==null)
{str="";
}
if(str.equals("yes"))
{response.setContentType("application/msword;charset=GB2312");
}
%>
</FONT>
</BODY>
</HTML>错误报告：
HTTP Status 500 -type Exception reportmessagedescription The server encountered an internal error () that prevented it from fulfilling this request.exceptionorg.apache.jasper.JasperException: java.lang.IllegalStateException: Exception occurred when flushing data
       org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:532)
       org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:420)
       org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
       org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
       javax.servlet.http.HttpServlet.service(HttpServlet.java:803)root causejava.lang.IllegalStateException: Exception occurred when flushing data
       org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:194)
       org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:119)
       org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:78)
       org.apache.jsp.example3_005f10_jsp._jspService(example3_005f10_jsp.java:89)
       org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
       javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
       org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:384)
       org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
       org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
       javax.servlet.http.HttpServlet.service(HttpServlet.java:803)root causejava.io.UnsupportedEncodingException: GB2313
       sun.io.Converters.getConverterClass(Unknown Source)
       sun.io.Converters.newConverter(Unknown Source)
       sun.io.CharToByteConverter.getConverter(Unknown Source)
       sun.nio.cs.StreamEncoder$ConverterSE.<init>(Unknown Source)
       sun.nio.cs.StreamEncoder$ConverterSE.<init>(Unknown Source)
       sun.nio.cs.StreamEncoder.forOutputStreamWriter(Unknown Source)
       java.io.OutputStreamWriter.<init>(Unknown Source)
       org.apache.tomcat.util.buf.WriteConvertor.<init>(C2BConverter.java:174)
       org.apache.tomcat.util.buf.C2BConverter.<init>(C2BConverter.java:47)
       org.apache.catalina.connector.OutputBuffer.setConverter(OutputBuffer.java:520)
       org.apache.catalina.connector.OutputBuffer.checkConverter(OutputBuffer.java:486)
       org.apache.catalina.connector.Response.getWriter(Response.java:624)
       org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)
       org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
       org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)
       org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:191)
       org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:119)
       org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:78)
       org.apache.jsp.example3_005f10_jsp._jspService(example3_005f10_jsp.java:89)
       org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
       javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
       org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:384)
       org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
       org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
       javax.servlet.http.HttpServlet.service(HttpServlet.java:803)小的真心求助……呜呜，卡了半天了……