运用Filter，ThreadLocal和Reflection，实现form到bean的填充

 if(beanMethod != null) {
                    try {
                        beanMethod.invoke(beanObject, fieldValue);
                    } catch (IllegalArgumentException ex) {
                        request.setAttribute("MainErrMsg", "illegal argument for the method " + sb.toString() + " of " + beanName);
                        this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                        return;
                    } catch (InvocationTargetException ex) {
                        request.setAttribute("MainErrMsg", beanName + " invoke target exception ");
                        this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                        return;
                    } catch (IllegalAccessException ex) {
                        request.setAttribute("MainErrMsg", beanName + " illegal access to " + sb.toString());
                        this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                        return;
                    }
                }
            }
            Form2BeanUtil.put(beanObject);
           
            Method getAllErrors = null;
            try {
                getAllErrors = beanClazz.getDeclaredMethod("getAllErrors");
            } catch (SecurityException ex) {
                System.err.println("Security exception when call getAllErrors()");
            } catch (NoSuchMethodException ex) {
                System.err.println("No such method named getAllErrors()");
            }
           
            if(getAllErrors != null) {
                try {
                    isValid = ((HashMap)getAllErrors.invoke(beanObject)).isEmpty();
                } catch (IllegalArgumentException ex) {
                    System.err.println("Illegal argument for getAllErrors()");
                } catch (IllegalAccessException ex) {
                    System.err.println("Illegal Access to getAllErrors()");
                } catch (InvocationTargetException ex) {
                    System.err.println("Invocation target exception");
                }
            }
        }
       
        if(beanName == null || isValid) {
            chain.doFilter(request, response);
        } else {
            if(beanObject != null) {
                request.setAttribute("formbean", beanObject);
            }
            this.filterConfig.getServletContext().getRequestDispatcher(getRequestURI(request)).forward(request, response);
        }
    }

    /**
     * Destroy method for this filter
     *
     */
    public void destroy() {
    }

    public String getRequestURI(ServletRequest request) {
        String requestURI = ((HttpServletRequest)request).getRequestURI();
        String queryString = ((HttpServletRequest)request).getQueryString();
        return requestURI + queryString;
    }
   
    /**
     * Return a String representation of this object.
     */
    public String toString() {
       
        if (filterConfig == null) return ("SimpleFilter()");
        StringBuffer sb = new StringBuffer("SimpleFilter(");
        sb.append(filterConfig);
        sb.append(")");
        return (sb.toString());
    }

}