NSDate 格式化 NSDate to NSString

NSLog(@"%@",[NSDate stringFromDate:[NSDate date] withFormat:@"yyyyMMdd__HH_mm_ss_zzz"]);     

输出结果为：

2015-09-15 17:08:08.720 IconMaker[23584:592901] 20150915__17_08_08_GMT+8