NSURLConnection

    // 0.请求路径
    NSURL *url = [NSURL URLWithString:@"http://XXX.XXX.XXX.XXX:32812/login?username=123&pwd=345"];
   
    // 1.创建请求对象
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    // 2.发送请求
    // sendSynchronousRequest阻塞式的方法，等待服务器返回数据
    
    NSHTTPURLResponse *response = nil;
    NSError *error = nil;
    
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
    
    // 3.解析服务器返回的数据（解析成字符串）
    NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@ %@", string, response.allHeaderFields);

    // 0.请求路径
    NSURL *url = [NSURL URLWithString:@"http://XXX.XXX.XXX.XXX:32812/login?username=123t&pwd=123"];
    
    // 1.创建请求对象
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    // 2.发送请求
    [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        // 请求完毕会来到这个block
        // 3.解析服务器返回的数据（解析成字符串）
        NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"%@", string);
        //        NSHTTPURLResponse *r = (NSHTTPURLResponse *)response;
        //
        //        NSLog(@"%zd %@", r.statusCode, r.allHeaderFields);
    }];

- (void)delegateAysnc
{
    // 0.请求路径
    NSURL *url = [NSURL URLWithString:@"http://XXX.XXX.XXX.XXX:32812/login?username=122&pwd=123"];
    
    // 1.创建请求对象
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    // 2.创建连接对象
//    [[NSURLConnection alloc] initWithRequest:request delegate:self];
    
//    NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
//    [conn start];
    
    [NSURLConnection connectionWithRequest:request delegate:self];
    
    // 取消
//    [conn cancel];
}

#pragma mark - <NSURLConnectionDataDelegate> -- being
/**
 * 接收到服务器的响应
 */
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // 创建data对象
    self.responseData = [NSMutableData data];
    NSLog(@"didReceiveResponse");
}

/**
 * 接收到服务器的数据（如果数据量比较大，这个方法会被调用多次）
 */
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // 不断拼接服务器返回的数据
    [self.responseData appendData:data];
    NSLog(@"didReceiveData -- %zd", data.length);
}

/**
 * 服务器的数据成功接收完毕
 */
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"connectionDidFinishLoading");
    NSString *string = [[NSString alloc] initWithData:self.responseData encoding:NSUTF8StringEncoding];
    NSLog(@"%@", string);
    
    self.responseData = nil;
}

/**
 * 请求失败（比如请求超时）
 */
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"didFailWithError -- %@", error);
}
#pragma mark - <NSURLConnectionDataDelegate> -- end

 1.请求路径
    NSURL *url = [NSURL URLWithString:@"http://XXX.XXX.XXX.XXX:32812/login"];
    
    // 2.创建请求
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    // 更改请求方法
    request.HTTPMethod = @"POST";
    // 设置请求体
    request.HTTPBody = [@"username=123&pwd=123" dataUsingEncoding:NSUTF8StringEncoding];
    // 设置超时(5秒后超时)
    request.timeoutInterval = 5;
    // 设置请求头
//    [request setValue:@"iOS 9.0" forHTTPHeaderField:@"User-Agent"];
    
    // 3.发送请求
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        if (connectionError) { // 比如请求超时
            NSLog(@"----请求失败");
        } else {
            NSLog(@"------%@", [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
        }
    }];

- (void)post
{
    // 0.请求路径
    NSString *urlStr = @"http://XXX.XXX.XXX.XXX:32812/login2";
    NSURL *url = [NSURL URLWithString:urlStr];
    
    // 1.创建请求对象
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    request.HTTPMethod = @"POST";
    request.HTTPBody = [@"username=POST请求&pwd=123" dataUsingEncoding:NSUTF8StringEncoding];
    
    // 2.发送请求
    [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        // 3.解析服务器返回的数据（解析成字符串）
        NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"%@", string);
    }];
}

- (void)get
{
    // 0.请求路径
    NSString *urlStr = @"http://XXX.XXX.XXX.XXX:32812/login2?username=GET请求&pwd=123";
    // 将中文URL进行转码
    urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSURL *url = [NSURL URLWithString:urlStr];
    
    // 1.创建请求对象
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    // 2.发送请求
    [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        // 3.解析服务器返回的数据（解析成字符串）
        NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"%@", string);
    }];
}