清楚webView的缓存

+(void)clearCache
{
    NSHTTPCookie *cookie;
    NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage];
    for (cookie in [storage cookies])
    {
        [storage deleteCookie:cookie];
    }
    
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
}