1.缓存策略详见API

public enum NSURLRequestCachePolicy : UInt {
    //缓存策略定义在 web 协议实现中，用于请求特定的URL。是默认的URL缓存策略
    case UseProtocolCachePolicy

    //从服务端获取数据，忽略本地缓存
    case ReloadIgnoringLocalCacheData

    //不仅忽略本地的缓存数据，还忽略中间网络媒介（如代理服务器）忽略缓存。直接从最原始的服务器拿取
    case ReloadIgnoringLocalAndRemoteCacheData // Unimplemented

    //被NSURLRequestReloadIgnoringLocalCacheData替换了
Replaced by NSURLRequestReloadIgnoringLocalCacheData.
    public static var ReloadIgnoringCacheData: NSURLRequestCachePolicy { get }

    //已经存在的缓存数据用于请求返回，不管它的过期日期和已经存在了多久。如果没有请求对应的缓存数据，从数据源读取
    case ReturnCacheDataElseLoad

    //已经存在的缓存数据用于请求返回，不管它的过期日期和已经存在了多久。如果没有请求对应的缓存数据，不要去数据源读取，该请求被设置为失败，这种情况多用于离线模式
    case ReturnCacheDataDontLoad

     //已经存在的缓存数据先去数据源验证有效性，如果无效，将从数据源获取
    case ReloadRevalidatingCacheData // Unimplemented
}

2.上部分关键代码

class BaseWebViewController: UIViewController,UIWebViewDelegate {
     /// UIWebView
    lazy var webView:UIWebView
        = {
            let web = UIWebView(frame: CGRectZero).then({
                let cookies = NSHTTPCookieStorage.sharedHTTPCookieStorage().cookiesForURL(self.requestURL!)
                var request = NSMutableURLRequest(URL: self.requestURL!)
                //判断请求方式
                if self.requestURL?.absoluteString.containsString(API_shoppingCart) == true {
                  request.HTTPMethod = "POST"
                }else{
                  request.HTTPMethod = "GET"
                }
                //缓存策略定义在 web 协议实现中，用于请求特定的URL。是默认的URL缓存策略
                request.cachePolicy = .UseProtocolCachePolicy
                //对象代表一个HTTP cookie。 这是一个不可改变的对象，从一个包含cookie的属性的字典初始化,这个类可以用来手动创建cookie的Properties 。
                request.HTTPShouldHandleCookies = true
                request.allHTTPHeaderFields = NSHTTPCookie.requestHeaderFieldsWithCookies(cookies!)
                $0.loadRequest(request)
            })
            return web
    }()


     func webView(webView: UIWebView, shouldStartLoadWithRequest request: NSURLRequest, navigationType: UIWebViewNavigationType) -> Bool{
          //判断是否为购物车URL
          if request.URL?.absoluteString == API_shoppingCart {

            //获取session_id
            let session_id = (NSUserDefaults.standardUserDefaults().valueForKey("session_id") as? String) ?? ""

            var shoppingCart = ""

            //判断登录状态 1为未登录,然后相应根据session_id拼接URL
            if   let user_id = HLCheckUserID(true) == 1 {
                shoppingCart = API_shoppingCart + "&session_id=\(session_id.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet())!)" + "&user_id="
            }else{
                shoppingCart = API_shoppingCart + "&session_id=\(session_id.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet())!)" + "&user_id=\(HLCheckUserID(true))"
            }
    
            let newRequest = NSMutableURLRequest(URL: NSURL(string: shoppingCart)!)
            
            let cookies = NSHTTPCookieStorage.sharedHTTPCookieStorage().cookiesForURL(NSURL(string: shoppingCart)!)
            newRequest.HTTPMethod = "POST"
            newRequest.cachePolicy = .UseProtocolCachePolicy
            newRequest.HTTPShouldHandleCookies = true
            newRequest.allHTTPHeaderFields = NSHTTPCookie.requestHeaderFieldsWithCookies(cookies!)
            webView.loadRequest(newRequest)
            return false
        }
       return true
  }

    func webViewDidFinishLoad(webView: UIWebView){ 
        //对cookie进行缓存处理
        saveSessionIDCookie()

   }

//对cookie进行缓存处理
    func saveSessionIDCookie() {
        let cookiesToSet = NSHTTPCookieStorage.sharedHTTPCookieStorage().cookiesForURL(requestURL!)!
        var tempCookies: [NSHTTPCookie] = []
        for cookie in cookiesToSet {
            
            let params = [NSHTTPCookieValue: cookie.value, NSHTTPCookieName: cookie.name, NSHTTPCookiePath: cookie.path, NSHTTPCookieDomain: cookie.domain, NSHTTPCookieExpires: NSDate(timeIntervalSinceNow: 3600*24*30)]
            let tempCookie = NSHTTPCookie(properties: params)
            tempCookies.append(tempCookie!)
        }
        NSHTTPCookieStorage.sharedHTTPCookieStorage().setCookies(tempCookies, forURL: requestURL!, mainDocumentURL: nil)
    }
    

}