java 日期的格式化 输入/输出

想要得到形如2018.07.09的格式化好的当天日期

创建Date对象，调用SimpleDateFormat对象的format方法：

indexstr="logstash-"+new SimpleDateFormat("yyyy.MM.dd").format(new Date());

package com.ob;  

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;  

public class DateTest {  

    public static void main(String[] args) throws ParseException {
        Calendar now = Calendar.getInstance();
        System.out.println("年: " + now.get(Calendar.YEAR));
        System.out.println("月: " + (now.get(Calendar.MONTH) + ) + "");
        System.out.println("日: " + now.get(Calendar.DAY_OF_MONTH));
        System.out.println("时: " + now.get(Calendar.HOUR_OF_DAY));
        System.out.println("分: " + now.get(Calendar.MINUTE));
        System.out.println("秒: " + now.get(Calendar.SECOND));
        System.out.println("当前时间毫秒数：" + now.getTimeInMillis());
        System.out.println(now.getTime());  

        Date d = new Date();
        System.out.println(d);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateNowStr = sdf.format(d);
        System.out.println("格式化后的日期：" + dateNowStr);  

        String str = "2012-1-13 17:26:33";  //要跟上面sdf定义的格式一样
        Date today = sdf.parse(str);
        System.out.println("字符串转成日期：" + today);
    }
}  

输出结果：

年: 2012
月: 1
日: 13
时: 17
分: 28
秒: 19
当前时间毫秒数：1326446899902
Fri Jan 13 17:28:19 CST 2012
Fri Jan 13 17:28:19 CST 2012
格式化后的日期：2012-01-13 17:28:19
字符串转成日期：Fri Jan 13 17:26:33 CST 2012

参考https://blog.csdn.net/qq_29347295/article/details/77482694