java中String类型转换为yyyy-MM-dd的Date类型

String转为Date

String birthday ="2017-02-22";

SimpleDateFormat sdf = new SimpleDateFormat(("yyyy-MM-dd"));
java.util.Date date = null;
try {
date = sdf.parse(birthday);
} catch (ParseException e) {
e.printStackTrace();
} 
System.out.println(new java.sql.Date(date.getTime()));

Date转为String

String sdate;  
Date ddate;  
……  
sdate=(new SimpleDateFormat("yyyy-MM-dd")).format(ddate);