URL的幾個簡單方法以及很初級的同步和異步

@implementation ViewController
            
- (void)viewDidLoad {
    [super viewDidLoad];
    
    //創建一個URL
    NSURL *url = [NSURL URLWithString:@"http://www.baidu.com/"];
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    NSLog(@"%@",[request HTTPMethod]);
    
    NSLog(@"%@",[request allHTTPHeaderFields]);
    
    //獲取請求的地址
    NSLog(@"%@",[request URL]);
    
    //對這個請求進行緩存優化
    [request cachePolicy];
    
    //這是一個同步的方法
//    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
//    NSLog(@"%d",data.length);
//    NSLog(@"結束了");
    
    //這是一個異步的方法
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectError){
        NSLog(@"%d",data.length);
    }];
    NSLog(@"end");
}