How to get the current time and current timestamp in iOS

//Get the current time+(NSString*)getCurrentTimes{
 NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
 // ------------Set the format you want, the difference between hh and HH: respectively representing 12-hour system and 24-hour system [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
 // Now, you can output to see what format it is NSDate *datenow = [NSDate date];
 //-------------Convert nsdate to nsstring in formatter format NSString *currentTimeString = [formatter stringFromDate:datenow];
 NSLog(@"currentTimeString = %@",currentTimeString);
 return currentTimeString;
}

+(NSString *)getNowTimeTimestamp{
 NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
 [formatter setDateStyle:NSDateFormatterMediumStyle];
 [formatter setTimeStyle:NSDateFormatterShortStyle];
 [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"]; // ------------Set the format you want, the difference between hh and HH: respectively representing 12-hour system and 24-hour system //Set the time zone, this is sometimes very important for time processing NSTimeZone* timeZone = [NSTimeZone timeZoneWithName:@"Asia/Shanghai"];
 [formatter setTimeZone:timeZone];
 NSDate *datenow = [NSDate date];// Now, you can output to see what format it is NSString *timeSp = [NSString stringWithFormat:@"%ld", (long)[datenow timeIntervalSince1970]];
 return timeSp;
}
+(NSString *)getNowTimeTimestamp2{
 NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
 NSTimeInterval a=[dat timeIntervalSince1970];
 NSString*timeString = [NSString stringWithFormat:@"%", a];//Convert to character type ;
return timeString;
}
 //Get the current timestamp (in milliseconds)+(NSString *)getNowTimeTimestamp3{
 NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
 [formatter setDateStyle:NSDateFormatterMediumStyle];
 [formatter setTimeStyle:NSDateFormatterShortStyle];
 [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss SSS"]; // ------------Set the format you want, the difference between hh and HH: respectively representing 12-hour system and 24-hour system //Set the time zone, this is sometimes very important for time processing NSTimeZone* timeZone = [NSTimeZone timeZoneWithName:@"Asia/Shanghai"];
 [formatter setTimeZone:timeZone];
 NSDate *datenow = [NSDate date];// Now, you can output to see what format it is NSString *timeSp = [NSString stringWithFormat:@"%ld", (long)[datenow timeIntervalSince1970]*1000];
 return timeSp;
}