1.NSURLsessionDataTask

 1     // 确定URL
 2     NSString *urlStr = @"http://localhost/试试看";
 3     urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
 4     NSURL *url = [NSURL URLWithString:urlStr];
 5     
 6     // 确定request
 7     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:0 timeoutInterval:2.0f];
 8     
 9     // 确定会话
10     NSURLSession *session = [NSURLSession sharedSession];
11     
12     // 由会话生成任务
13     NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
14         NSLog(@"response-- %@",response);
15         NSLog(@"data--%@",data);
16         
17         // 刷新UI,一定要返回主线程去刷新
18         dispatch_async(dispatch_get_main_queue(), ^{
19             [self.imageView  setImage:[UIImage imageWithData:data]];
20         });
21 
22     }];
23     // URLSession默认生成的任务都是挂起状态,需要使用以下语句执行任务
24     [dataTask resume];

2.NSURLSessionDownloadTask实现简单的下载功能

 1     // 确定URL
 2     NSString *urlStr = @"http://localhost/试试看";
 3     urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
 4     NSURL *url = [NSURL URLWithString:urlStr];
 5     
 6     // 确定request
 7     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:0 timeoutInterval:2.0f];
 8     
 9     // 确定会话
10     NSURLSession *session = [NSURLSession sharedSession];
11     
12     // 由会话生成任务
13     NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
14         // 从tmp中拷贝文件到cache
15         NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
16         NSURL *cachePathURL = [NSURL fileURLWithPath:cachePath];
17         NSString *fileNameBymd5 = [[[response URL] absoluteString] MD5];
18         NSURL *fileURL = [cachePathURL URLByAppendingPathComponent: fileNameByMD5];
19 
20         NSFileManager *mgr = [NSFileManager defaultManager];
21         [mgr moveItemAtURL:location toURL:fileURL  error:NULL];
22         
23     }];
24     
25     [downloadTask resume];

 1 - (NSString *)MD5
 2 {
 3     const char *cStr = [self UTF8String];
 4     unsigned char digest[CC_MD5_DIGEST_LENGTH];
 5 
 6     CC_MD5(cStr, strlen(cStr), digest);
 7 
 8     NSMutableString *result = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
 9 
10     for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) {
11         [result appendFormat:@"%02x", digest[i]];
12     }
13 
14     return result;
15 }

3.NSURLSessionDownloadTask实现复杂的下载功能:断点续传\后台下载

http://blog.csdn.net/majiakun1/article/details/38133789