IOS 长链接与短链接之间的转换

#import <CommonCrypto/CommonDigest.h> @interface NSString (md5) -(NSString *) md5HexDigest; @end

#import "NSString+md5.h" @implementation NSString (md5) - (NSString *) md5HexDigest{  const char *original_str = [self UTF8String];  unsignedchar result[CC_MD5_DIGEST_LENGTH];  CC_MD5(original_str, strlen(original_str), result);  NSMutableString *hash = [NSMutableStringstring];  for (int i = 0; i < 16; i++)    [hash appendFormat:@"%02X", result[i]];  NSLog(@"lowercaseString = %@",[hash lowercaseString]);  return [hash lowercaseString];} @end

- (NSString *)shortUrl:(NSString *)url{  NSArray *chars = [[NSArray alloc] initWithObjects:@"a" , @"b" , @"c" , @"d" , @"e" , @"f" , @"g" , @"h" ,           @"i" , @"j" , @"k" , @"l" , @"m" , @"n" , @"o" , @"p" , @"q" , @"r" , @"s" , @"t" ,           @"u" , @"v" , @"w" , @"x" , @"y" , @"z" , @"0" , @"1" , @"2" , @"3" , @"4" , @"5" ,           @"6" , @"7" , @"8" , @"9" , @"A" , @"B" , @"C" , @"D" , @"E" , @"F" , @"G" , @"H" ,           @"I" , @"J" , @"K" , @"L" , @"M" , @"N" , @"O" , @"P" , @"Q" , @"R" , @"S" , @"T" ,           @"U" , @"V" , @"W" , @"X" , @"Y" , @"Z", nil];  NSLog(@"chars = %d", [chars count]);  NSString *key = @"xxxxxx";  NSString *hex = [NSStringstringWithFormat:@"%@",[[key stringByAppendingFormat:@"%@",url] md5HexDigest]];   NSLog(@"hex = %@", hex);  NSMutableArray *resUrl = [[NSMutableArrayalloc] initWithCapacity:4];  for (int i=0; i<4; i++) {    // 把加密字符按照 8 位一组 16 进制与 0x3FFFFFFF 进行位与运算    NSString *sTempSubString = [hex substringWithRange:NSMakeRange(i*8, 8)];        // 这里需要使用 long 型来转换，因为 Inteper只能处理 31 位 , 首位为符号位 , 如果不用 long ，则会越界    long longOfTemp;    sscanf([sTempSubString cStringUsingEncoding:NSASCIIStringEncoding], "%lx", &longOfTemp);    long lHexLong = 0x3FFFFFFF & longOfTemp;    NSString *outChars = @"";    for (int j=0; j<6; j++) {      // 把得到的值与 0x0000003D 进行位与运算，取得字符数组 chars 索引      long index = 0x0000003D & lHexLong;      // 把取得的字符相加      outChars = [outChars stringByAppendingFormat:@"%@",[chars objectAtIndex:(int)index]];      // 每次循环按位右移 5 位      lHexLong = lHexLong >> 5;    }    // 把字符串存入对应索引的输出数组    [resUrl insertObject:outChars atIndex:i];  }  return [resUrl objectAtIndex:0];//这里可以返回任意一个元素作为短链接（0，1，2，3）}