为什么下面程序的“清空”按钮失效？？
<%@ page contentType="text/html;charset=GB2312"%>
<%@ page import="Factory.*"%>
<%@ page import="lists.*"%>

<center>
<%
        request.setCharacterEncoding("GB2312");
    String str1=(String)session.getAttribute("name");
    String str2=request.getParameter("title");
    lists L=new lists();
        if(str1!=null)
        {
            L.setTitle(str2);
                L=Factory.getListDAOImpl().queryByTitle(L);
%>
                <h1>留言管理</h1>
                <hr>
                <form action="update.jsp" method="post">
                <table>
                    <tr>
                        <td align="center" colspan=2><font color="blue">修改留言</font></td></tr>
                    <tr>
                        <td>标题:</td>
                        <td><input type="text" name="title" value=<%=L.getTitle()%>></td></tr>
                    <tr>
                        <td>作者</td>
                        <td><input type="text" name="author" value=<%=L.getAuthor()%>></td></tr>
                    <tr>
                        <td>内容:</td>
                        <td><textarea cols=30 rows=8 name="content"><%=L.getContent()%></textarea></td></tr>
                    <tr>
                        <td><input type="reset" value="清空"></td></tr>  
                    <tr>
                        <td>&nbsp;</td></tr>
                    <tr>    
                        <td align="center" colspan=2><a href="list_notes.jsp">回到留言列表页</a></td></tr>
                </table>
              </form>
<%
    }
    else 
    {
                    response.setHeader("refresh","2;url=login.jsp");
%>
                  <div align="center"><font size=5>你还没有登陆,请先登陆!!<br>
                  2秒后自动跳转到登陆页<br>
              如果没有跳转,请按<a href="login.jsp">这里</a></font></div>    
<%
        }            
%>    
</center>