iOS 文件下载

#import <Foundation/Foundation.h>

@interface NSString (Password)

/**
*  32位MD5加密
*
*  @return 32位MD5加密结果
*/
- (NSString *)MD5;

/**
*  SHA1加密
*
*  @return SHA1加密结果
*/
- (NSString *)SHA1;

@end

#import "NSString+Password.h"
#import <CommonCrypto/CommonDigest.h>

@implementation NSString (Password)

#pragma mark 使用MD5加密字符串
- (NSString *)MD5
{
const char *cStr = [self UTF8String];
unsigned char digest[CC_MD5_DIGEST_LENGTH];

CC_MD5(cStr, strlen(cStr), digest);

NSMutableString *result = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];

for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) {
[result appendFormat:@"%02x", digest[i]];
}

return result;
}

#pragma mark 使用SHA1加密字符串
- (NSString *)SHA1
{
const char *cStr = [self UTF8String];
NSData *data = [NSData dataWithBytes:cStr length:self.length];
uint8_t digest[CC_SHA1_DIGEST_LENGTH];

CC_SHA1(data.bytes, data.length, digest);

NSMutableString *result = [NSMutableString stringWithCapacity:CC_SHA1_DIGEST_LENGTH * 2];

for(int i = 0; i < CC_SHA1_DIGEST_LENGTH; i++) {
[result appendFormat:@"%02x", digest[i]];
}

return result;
}

@end

FileDownload

#import <Foundation/Foundation.h>

@interface FileDownload : NSObject

- (void)downloadFileWithURL:(NSURL *)url completion:(void (^)(UIImage *image))completion;
@end

#import "FileDownload.h"
#import "NSString+Password.h"

#define kTimeOut        2.0f
// 每次下载的字节数
#define kBytesPerTimes  20250

@interface FileDownload()
@property (nonatomic, strong) NSString *cacheFile;
@property (nonatomic, strong) UIImage *cacheImage;
@end

@implementation FileDownload
/**
为了保证开发的简单,所有方法都不使用多线程,所有的注意力都保持在文件下载上

在开发中如果碰到比较绕的计算问题时,建议:
1> 测试数据不要太大
2> 测试数据的数值变化,能够用笔算计算出准确的数值
3> 编写代码对照测试

*/
//- (NSString *)cacheFile
//{
//    if (!_cacheFile) {
//        NSString *cacheDir = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0];
//        _cacheFile = [cacheDir stringByAppendingPathComponent:@"123.png"];
//    }
//    return _cacheFile;
//}
- (UIImage *)cacheImage
{
if (!_cacheImage) {
_cacheImage = [UIImage imageWithContentsOfFile:self.cacheFile];
}
return _cacheImage;
}

- (void)setCacheFile:(NSString *)urlStr
{
NSString *cacheDir = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0];
urlStr = [urlStr MD5];

_cacheFile = [cacheDir stringByAppendingPathComponent:urlStr];
}

- (void)downloadFileWithURL:(NSURL *)url completion:(void (^)(UIImage *image))completion
{
// GCD中的串行队列异步方法
dispatch_queue_t q = dispatch_queue_create("cn.itcast.download", DISPATCH_QUEUE_SERIAL);

dispatch_async(q, ^{
NSLog(@"%@", [NSThread currentThread]);

// 把对URL进行MD5加密之后的结果当成文件名
self.cacheFile = [url absoluteString];

// 1. 从网络下载文件,需要知道这个文件的大小
long long fileSize = [self fileSizeWithURL:url];
// 计算本地缓存文件大小
long long cacheFileSize = [self localFileSize];

if (cacheFileSize == fileSize) {
dispatch_async(dispatch_get_main_queue(), ^{
completion(self.cacheImage);
});
NSLog(@"文件已经存在");
return;
}

// 2. 确定每个数据包的大小
long long fromB = 0;
long long toB = 0;
// 计算起始和结束的字节数
while (fileSize > kBytesPerTimes) {
// 20480 + 20480
//
toB = fromB + kBytesPerTimes - 1;

// 3. 分段下载文件
[self downloadDataWithURL:url fromB:fromB toB:toB];

fileSize -= kBytesPerTimes;
fromB += kBytesPerTimes;
}
[self downloadDataWithURL:url fromB:fromB toB:fromB + fileSize - 1];

dispatch_async(dispatch_get_main_queue(), ^{
completion(self.cacheImage);
});
});
}

#pragma mark 下载指定字节范围的数据包
/**
NSURLRequestUseProtocolCachePolicy = 0,        // 默认的缓存策略,内存缓存

NSURLRequestReloadIgnoringLocalCacheData = 1,  // 忽略本地的内存缓存
NSURLRequestReloadIgnoringCacheData
*/
- (void)downloadDataWithURL:(NSURL *)url fromB:(long long)fromB toB:(long long)toB
{
NSLog(@"数据包:%@", [NSThread currentThread]);

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:kTimeOut];

// 指定请求中所要GET的字节范围
NSString *range = [NSString stringWithFormat:@"Bytes=%lld-%lld", fromB, toB];
[request setValue:range forHTTPHeaderField:@"Range"];
NSLog(@"range----%@", range);

NSURLResponse *response = nil;
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL];

// 写入文件,覆盖文件不会追加
//    [data writeToFile:@"/Users/aplle/Desktop/1.png" atomically:YES];
[self appendData:data];

NSLog(@"response*******%@", response);
}

#pragma mark - 读取本地缓存文件大小
- (long long)localFileSize
{
// 读取本地文件信息
NSDictionary *dict = [[NSFileManager defaultManager] attributesOfItemAtPath:self.cacheFile error:NULL];
NSLog(@"读取本地文件信息%lld", [dict[NSFileSize] longLongValue]);

return [dict[NSFileSize] longLongValue];
}

#pragma mark - 追加数据到文件
- (void)appendData:(NSData *)data
{
// 判断文件是否存在
NSFileHandle *fp = [NSFileHandle fileHandleForWritingAtPath:self.cacheFile];
// 如果文件不存在创建文件
if (!fp) {
[data writeToFile:self.cacheFile atomically:YES];
} else {
// 如果文件已经存在追加文件
// 1> 移动到文件末尾
[fp seekToEndOfFile];
// 2> 追加数据
[fp writeData:data];
// 3> 写入文件
[fp closeFile];
}
}

#pragma mark - 获取网络文件大小
- (long long)fileSizeWithURL:(NSURL *)url
{
// 默认是GET
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:0 timeoutInterval:kTimeOut];

// HEAD 头,只是返回文件资源的信息,不返回具体是数据
// 如果要获取资源的MIMEType,也必须用HEAD,否则,数据会被重复下载两次
request.HTTPMethod = @"HEAD";

// 使用同步方法获取文件大小
NSURLResponse *response = nil;

[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL];

// expectedContentLength文件在网络上的大小
NSLog(@"%lld", response.expectedContentLength);
return response.expectedContentLength;
}
@end

#import "MJViewController.h"
#import "FileDownload.h"

@interface MJViewController ()
@property (nonatomic, strong) FileDownload *download;
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@end

@implementation MJViewController

- (void)viewDidLoad
{
[super viewDidLoad];

self.download = [[FileDownload alloc] init];
// http://image.zcool.com.cn/56/13/1308200901454.jpg [self.download downloadFileWithURL:[NSURL URLWithString:@"http://image.zcool.com.cn/56/13/1308200901454.jpg"] completion:^(UIImage *image) {

self.imageView.image = image;
}];
}

@end