新手上路，问servlet过滤器问题，跪求高手解答，谢谢

我写的servlet过滤器好像没用，根本没起到过滤的作用，请高手指点
JSP页面<%@ page contentType="text/html; charset=GBK" %>
<html>
<head>
<title>
hello
</title>
</head>
<body bgcolor="#ffffff">
<h1>
JBuilder Generated JSP
</h1>
<form method="post" action="/JspServletapp/testservlet">
<br><br>
  <input type="text" name="user" value="">
<input type="submit" name="Submit" value="Submit"></form>
</body>
</html>servlet过滤器
package jspservlet;import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;public class FiterServlet implements Filter {
  private FilterConfig filterConfig;  //Handle the passed-in FilterConfig
  public void init(FilterConfig filterConfig) throws ServletException {
    this.filterConfig = filterConfig;
  }  //Process the request/response pair
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) {
    try {      String userName = ((HttpServletRequest)request).getParameter("user");
      if(userName == "ddd")
      {
        userName = "dd";
      }
      else
      {
        filterChain.doFilter(request, response);
      }
    }
    catch(ServletException sx) {
      filterConfig.getServletContext().log(sx.getMessage());
    }
    catch(IOException iox) {
      filterConfig.getServletContext().log(iox.getMessage());
    }
  }  //Clean up resources
  public void destroy() {
  }
}我在JSP页面的文本框中输入ddd，servlet过滤器没用，还是跳到下个SERVLET了
servlet
package jspservlet;import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;public class TestServlet extends HttpServlet {
  private static final String CONTENT_TYPE = "text/html; charset=GBK";  //Initialize global variables
  public void init() throws ServletException {
  }  //Process the HTTP Get request
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType(CONTENT_TYPE);
    String userName= request.getParameter("user");
    PrintWriter out = response.getWriter();
    out.println("<html>");
    out.println("<head><title>TestServlet</title></head>");
    out.println("<body bgcolor=\"#ffffff\">");
    out.println("<p>The servlet has received a GET. This is the reply.</p>");
    out.println("<i>"+userName+"</i><br>");
    out.println("</body></html>");  }  //Clean up resources
  public void destroy() {
  }
}
web.xml<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
  <filter>
    <filter-name>fiterservlet</filter-name>
    <filter-class>jspservlet.FiterServlet</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>fiterservlet</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <servlet>
    <servlet-name>testservlet</servlet-name>
    <servlet-class>jspservlet.TestServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>testservlet</servlet-name>
    <url-pattern>/testservlet</url-pattern>
  </servlet-mapping>
</web-app>请高手来看下