如何修改HttpServletRequest

public class MyHttpServletRequestWrapper extends HttpServletRequestWrapper {
    Map<String, String[]> params = null;

    public MyHttpServletRequestWrapper(HttpServletRequest request, Map inParam) {
        super(request);
        params = new HashMap(inParam);
    }

    public void setParameter(String key,String value){
        params.put(key, new String[]{value});
    }
    public void setParameter(String key,String[] values){
        params.put(key, values);
    }

    @Override
    public String getParameter(String name) {
        Object v = params.get(name);
        if (v == null) {
            return null;
        } else if (v instanceof String[]) {
            String[] strArr = (String[]) v;
            if (strArr.length > 0) {
                return strArr[0];
            } else {
                return null;
            }
        } else {
            return v.toString();
        }
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        return params;
    }

    @Override
    public Enumeration<String> getParameterNames() {
        Vector l = new Vector(params.keySet());
        return l.elements();
    }

    @Override
    public String[] getParameterValues(String name) {
        return params.get(name);
    }
}

public class MyFilter implements Filter{
    private static Log log = LogFactory.getLog(MyFilter.class);

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest http_req = (HttpServletRequest)req;
        MyHttpServletRequestWrapper myHttpServletRequestWrapper = new MyHttpServletRequestWrapper(http_req, req.getParameterMap());
        chain.doFilter(myHttpServletRequestWrapper, res);
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void destroy() {
    }
}