//没有接受到数据
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
/* This method is called when the server has determined that it has
enough information to create the NSURLResponse. It can be called
multiple times, for example in the case of a redirect, so each time
we reset the data. */
NSLog(@"webdata length is :%d",[webData length]);
[webData setLength:0];
NSLog(@"connection:didReceiveResponse:1");
}