jsp添加项目中文乱码问题！求助！

Question

做了个投票系统，当添加投票项item时，添加成功了，但是中文乱码，显示的是问号，我测试了下，发现从manage.jsp中获得的additem到add.jsp就无法正常显示中文，可是我有 String additem=new String(request.getParameter("additem").getBytes("iso8859-1"),"GBK");  请问到底是哪里出了问题？
  代码：manage.jsp
<%@page contentType="text/html;charset=GBK" import="java.sql.*" %><%@include file="check.jsp" %>
<jsp:useBean id="db" class="bean.QueryBean" scope="session"/>
<center>
<h2>系统维护</h2>
<table border bordercolor=blue>
<tr><th colspan="3" bgcolor=yellow>删除投票项</th>
<%
    
     request.setCharacterEncoding("GBK"); 
     Connection conn=db.setConnection("movie");
     ResultSet rs=db.getQuery("select * from vote");
     int i=1;
     while(rs.next())
     {
       out.println("<tr>");
       out.println("<td>"+i+"</td>");
       out.println("<td>"+rs.getString("item")+"</td>");
       out.println("<td align='center'><a href='delete.jsp?delid="+rs.getString("id")+"'>删除</a></td>");
       i++;
     }
%>
<tr><th colspan="3" bgcolor=blue>添加投票项</th>    
<tr><td colspan="3">
<form method="post" action="add.jsp">
内容：<input type="text" name="additem" size="30"/>
      <input type="submit" value=提交/>
      <input type="reset" value=重置/>
</form></td>
<tr><td colspan="3" align="center" ><a href="index.jsp">返回投票页面</a></td>
</table>  </td> add.jsp
<%@page contentType="text/html;charset=GBK" import="java.sql.*" %>
<jsp:useBean id="db" class="bean.QueryBean" scope="session"/>
  <%
   request.setCharacterEncoding("GBK"); 
   String additem=new String(request.getParameter("additem").getBytes("iso8859-1"),"GBK");
   System.out.println(additem);
   if(additem!=null)
   {
    String sql="insert into vote(item,c)values('"+additem +"','"+0+"')";
    db.setModify(sql);
    db.close();
    }
   %>
  <jsp:forward page="manage.jsp"/>  

Answer 1

数据库，开发环境，应用服务器使用统一的字符集，如：utf-8。这样是不会出现乱码的

Answer 2

加个过滤器，过滤你的jsp文件<filter>
<filter-name>EncodeingFilter</filter-name>
<filter-class>com.sail.cot.common.filter.EncodeingFilter</filter-class>
<init-param>
<description>是否配置编码过滤器</description>
<param-name>useEncoding</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<description>配置使用的编码格式</description>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>EncodeingFilter</filter-name>
<url-pattern>*.do</url-pattern>
<url-pattern>/servlet/*</url-pattern>
<url-pattern>*.action</url-pattern>
</filter-mapping>
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest httpRequest = (HttpServletRequest) request;
HttpServletResponse httpResponse = (HttpServletResponse) response;


httpRequest.setCharacterEncoding(defaultEncodeing);
httpResponse.setContentType("text/html; charset=" + defaultEncodeing);
httpResponse.setCharacterEncoding(defaultEncodeing);
        System.out.println("url is " + httpRequest.getRequestURI());
        //response.setContentType("text/xml;charset=utf-8");
        chain.doFilter(request, response);
}

Answer 3

request.setCharacterEncoding("GBK");  
  String additem=new String(request.getParameter("additem").getBytes("iso8859-1"),"GBK");
 应该这样
//request.setCharacterEncoding("GBK");  
String additem=new String(request.getParameter("additem").getBytes("iso8859-1"),"GBK");
要么request.setCharacterEncoding("GBK"); 
String additem= request.getParameter("additem");
 // String additem=new String(request.getParameter("additem").getBytes("iso8859- //1"),"GBK");

Answer 4

就是我的manage.jsp页面从add.jsp页面获得的item项是显示乱码的，怎么解决？刚试了下过滤器，可是运行时显示404错误啊！好像这种问题不用过滤器也能解决吧？