文件下载

小文件下载方式：原因是它们有一个致命的缺点就是必须下载完成后才能返还给nsdata，也就是说无法监测到下载进度，实用性差，也就只能用于一些小文件的下载。
1.NSData dataWithContentsOfURL
2.NSURLConnection

//.NSData dataWithContentsOfURL
- (void)downloadFile{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 其实这就是一个GET请求
NSURL *url = [NSURL URLWithString:@”http://localhost:8080/MJServer/resources/images/minion_01.png“];
NSData *data = [NSData dataWithContentsOfURL:url];
NSLog(@”%d”, data.length);
});
}

//NSURLConnection
- (void)downloadFile2{
NSURL *url = [NSURL URLWithString:@”http://localhost:8080/MJServer/resources/images/minion_01.png“];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
NSLog(@”%d”, data.length);
}];
}

大文件下载方式：
大文件下载方式1：（由于内存问题不可取，但需要了解）
- (void)download{
// 1.URL
NSURL *url = [NSURL URLWithString:@”http://localhost:8080/MJServer/resources/videos.zip“];
// 2.请求
NSURLRequest *request = [NSURLRequest requestWithURL:url];
// 3.下载(创建完conn对象后，会自动发起一个异步请求)
[NSURLConnection connectionWithRequest:request delegate:self];

// [[NSURLConnection alloc] initWithRequest:request delegate:self];
// [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
// NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];//为NO 表示只是连接并没有立马开始请求，所以与 [conn start];套用
// [conn start];
}

• (void)touchesBegan:(NSSet )touches withEvent:(UIEvent )event{
  [self download];
  }
• (void)connection:(NSURLConnection )connection didFailWithError:(NSError )error{
  NSLog(@”didFailWithError”);
  }
  
  • 1.接收到服务器的响应就会调用
• (void)connection:(NSURLConnection )connection didReceiveResponse:(NSURLResponse )response{
  NSLog(@”didReceiveResponse”);
  // 初始化数据
  self.fileData = [NSMutableData data];
  // 取出文件的总长度方式1：
  // NSHTTPURLResponse resp = (NSHTTPURLResponse )response;
  // long long fileLength = [resp.allHeaderFields[@”Content-Length”] longLongValue];
  // 取出文件的总长度方式2：
  self.totalLength = response.expectedContentLength;
  }

/**
* 2.当接收到服务器返回的实体数据时调用（具体内容，这个方法可能会被调用多次）
- (void)connection:(NSURLConnection )connection didReceiveData:(NSData )data{
// 拼接数据
[self.fileData appendData:data];
// 设置进度值
// 0 ~ 1
// self.progressView.progress = (double)self.fileData.length / self.totalLength;
self.circleView.progress = (double)self.fileData.length / self.totalLength;
}

• 3.加载完毕后调用（服务器的数据已经完全返回后）
  */
  
  • (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@”connectionDidFinishLoading”)；
    // 拼接文件路径
    NSString *cache = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *file = [cache stringByAppendingPathComponent:@”videos.zip”];
    // 写到沙盒中
    [self.fileData writeToFile:file atomically:YES];
    }

大文件下载方式2：
// 用来写数据的文件句柄对象
@property (nonatomic, strong) NSFileHandle *writeHandle;
// 文件的总大小
@property (nonatomic, assign) long long totalLength;
// 当前已经写入的文件大小
@property (nonatomic, assign) long long currentLength;

• (void)touchesBegan:(NSSet )touches withEvent:(UIEvent )event{
  // 1.URL
  NSURL *url = [NSURL URLWithString:@”http://localhost:8080/MJServer/resources/music.zip“];
  // 2.请求
  NSURLRequest *request = [NSURLRequest requestWithURL:url];
  // 3.下载(创建完conn对象后，会自动发起一个异步请求)
  [NSURLConnection connectionWithRequest:request delegate:self];
  }
  // 1.接收到服务器的响应就会调用
  
  • (void)connection:(NSURLConnection )connection didReceiveResponse:(NSURLResponse )response{
    // 文件路径
    NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *filepath = [caches stringByAppendingPathComponent:@”videos.zip”];
    // 创建一个空的文件 到 沙盒中
    NSFileManager *mgr = [NSFileManager defaultManager];
    [mgr createFileAtPath:filepath contents:nil attributes:nil];
    // 创建一个用来写数据的文件句柄
    self.writeHandle = [NSFileHandle fileHandleForWritingAtPath:filepath];
    // 获得文件的总大小
    self.totalLength = response.expectedContentLength;
    }
    // 2.当接收到服务器返回的实体数据时调用（具体内容，这个方法可能会被调用多次）
  • (void)connection:(NSURLConnection )connection didReceiveData:(NSData )data{
    // 移动到文件的最后面
    [self.writeHandle seekToEndOfFile];
    // 将数据写入沙盒
    [self.writeHandle writeData:data];
    // 累计文件的长度
    self.currentLength += data.length;
    NSLog(@”下载进度：%f”, (double)self.currentLength/ self.totalLength);
    self.circleView.progress = (double)self.currentLength/ self.totalLength;
    }
    // 3.加载完毕后调用（服务器的数据已经完全返回后）
  • (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    self.currentLength = 0;
    self.totalLength = 0;
    // 关闭文件
    [self.writeHandle closeFile];
    self.writeHandle = nil;
    }