[NSURLProtocol registerClass:[KKWebViewProtocol class]]; // 注册监听
@interface KKWebViewProtocol : NSURLProtocol
@end
// 判断是否拦截请求

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    return YES;
}
// 开始加载请求资源

+ (void)startLoading {
    // 再次获取cacheData
    NSURL *url = self.request.URL;
    NSData* cacheData = nil;
    if ([webViewProtocolDelegate respondsToSelector:@selector(dataForWebViewProtocolWithURL:)]) {
        // 拦截请求url 通过url查询是否存在已经缓存在本地的资源 如果存在则直接从本地读取返回NSData对象。如果不存在则返回null
        cacheData = [webViewProtocolDelegate dataForWebViewProtocolWithURL:[url absoluteString]];
        if (cacheData == nil) {
            // 发送网络请求
            self.downloadTask = [self.session dataTaskWithRequest:self.request];
            [self.downloadTask resume];
        }
        else{
            // 加载本地资源
            NSDictionary *dict = [NSDictionary dictionary];
            NSHTTPURLResponse* response = [[NSHTTPURLResponse alloc]
                                           initWithURL:url
                                           statusCode:200
                                           HTTPVersion:@"HTTP/2.0"
                                           headerFields:dict];
            [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
            [self.client URLProtocol:self didLoadData:cacheData];
            [self.client URLProtocolDidFinishLoading:self];
        }
    } else {
        self.downloadTask = [self.session dataTaskWithRequest:self.request];
        [self.downloadTask resume];
    }
}

// 停止资源加载
-(void)stopLoading{
    [self.downloadTask cancel];
    self.downloadTask = nil;
}

+ (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask*)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler {
    [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
    // 允许处理服务器的响应，才会继续接收服务器返回的数据
    completionHandler(NSURLSessionResponseAllow);
    self.cacheData = [NSMutableData data];
}

+ (void)URLSession:(NSURLSession *)session dataTask:(nonnull NSURLSessionDataTask*)dataTask didReceiveData:(nonnull NSData *)data{
    [self.client URLProtocol:self didLoadData:data];
    [self.cacheData appendData:data];
}

+ (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask*)task didCompleteWithError:(NSError *)error {
    // 下载完成之后的处理
    if (error) {
        [self.client URLProtocol:self didFailWithError:error];
    } else {
        //将数据存入到本地文件中
        [self.cacheData writeToFile:[self filePathWithUrlString:self.request.URL.absoluteString] atomically:YES];
        [self.client URLProtocolDidFinishLoading:self];
    }
}