NSURLConnection

    //同步方法發送請求並獲取返回數據
    NSURLResponse *response = [[NSURLResponse alloc]init];
    NSData *data = [NSURLConnection    sendSynchronousRequest:request returningResponse:&response error:nil];
    NSLog(@"%@",[(NSHTTPURLResponse *)response allHeaderFields]);
    
    NSLog(@"%d", [(NSHTTPURLResponse *)response statusCode]);
    常用方法：
    //異步方法發送請求下載
    NSURLConnection *_asyncConnect = nil;
    if(_asyncConnect == nil) {
    	NSURL *asyncURL = [NSURL URLWithString:@"http:// mirrors.163.com/ubuntu-releases/13.04/ubuntu-13.04- desktop-amd64.iso"];
        NSURLRequest *asyncRequest = [NSURLRequest requestWithURL:asyncURL];
        _asyncConnect = [[NSURLConnection alloc]initWithRequest:asyncRequest delegate:self];}
    //開始請求
    [_asyncConnect start]; 

集中常用的協議方法：

//請求連接出錯的處理方法
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(@“%@: failed:%@", [[connection currentRequest] URL], error);
}
//請求連接返回的響應頭的處理方法!
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
NSLog(@"response status code:%d",[(NSHTTPURLResponse *)response statusCode]);
NSLog(@"response expect length:%lld", [(NSHTTPURLResponse *)response expectedContentLength]);
NSLog(@"response all headfield:%@",[(NSHTTPURLResponse *)response allHeaderFields]);
}
//請求連接收到數據的處理方法,數據量大就可能會不斷調用
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
NSString *dataStr = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
NSLog(@"%@",dataStr);
}
//請求連接處理完成收據收發後的處理方法
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSSLog(@"connent to %@ finished", [[connection currentRequest] URL]);
}