时间类型

timestamp与String的相互转换
 用Timestamp来记录日期时间还是很方便的，但有时候显示的时候是不需要小数位后面的毫秒的，这样就需要在转换为String时重新定义格式。
 
      Timestamp转化为String:
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//定义格式，不显示毫秒
Timestamp now = new Timestamp(System.currentTimeMillis());//获取系统当前时间
String str = df.format(now);
 
      String转化为Timestamp:
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String time = df.format(new Date());
Timestamp ts = Timestamp.valueOf(time);

Date类型转换成String:

Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); 
String dBegin = sdf.format(date);

 SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//设置日期格式
 System.out.println(df.format(new Date()));// new Date()为获取当前系统时间

String类型转换成Date:

String start="2017-11-10";

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); 
Date dBegin = sdf.parse(start);

Calendar c = Calendar.getInstance();//可以对每个时间域单独修改
c.setTime(dBegin);
int year = c.get(Calendar.YEAR); 
int month = c.get(Calendar.MONDAY)+1; 
int weekday = c.get(Calendar.DAY_OF_WEEK); 
int day = c.get(Calendar.DATE); 
String week ="";
if (weekday == 1) {
week = "周日";
} else if (weekday == 2) {
week = "周一";
} else if (weekday == 3) {
week = "周二";
} else if (weekday == 4) {
week = "周三";
} else if (weekday == 5) {
week = "周四";
} else if (weekday == 6) {
week = "周五";
} else if (weekday == 7) {
week = "周六";
}