?//清除cookies
    NSHTTPCookie *cookie;
    NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage];
    for (cookie in [storage cookies])
    {
        [storage deleteCookie:cookie];
    }
 
    //清除UIWebView的缓存
    [[NSURLCache sharedURLCache] removeAllCachedResponses];?