同步和异步请求

同步和异步都是表态方法：

#pragma mark 异步请求
- (void)post2 {
    NSURL *url = [NSURL fileURLWithPath:@"/Users/apple/Desktop/备课.txt"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
   
    // 这个操作队列是用来执行Block的
    NSOperationQueue *queue = [[[NSOperationQueue alloc] init] autorelease];
    [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:
     // 请求结束后会回调这个Block
     ^(NSURLResponse *response, NSData *data, NSError *error) {
         NSString *str = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
         
         NSLog(@"%@", str);
         
         NSLog(@"%@", [response MIMEType]);
    }];
}

#pragma mark 同步请求-获取文件的MIMEType
- (void)getType {
    NSURL *url = [NSURL fileURLWithPath:@"/Users/apple/Desktop/备课.txt"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    // 发送一个同步请求
    NSURLResponse *response = nil;
    
    // 发送一个同步请求
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
    
    NSString *type = [response MIMEType];
    NSString *str = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
    
    NSLog(@"%@", str);
    NSLog(@"%@", type);
}