NSDateFormatter *dateFormtter=[[NSDateFormatter alloc] init];

[dateFormtter setDateFormat:@"yyyy-MM-dd"];

NSString *dateString=[dateFormtter stringFromDate:[dateFormtter dateFromString:@"2015-5-27"]];

NSLog(@"%@",dateString);

如果要不显示第一个0，可以写成@"yyyy-M-d"

@import url(http://i.cnblogs.com/Load.ashx?type=style&file=SyntaxHighlighter.css);@import url(/css/cuteeditor.css);