想要得到形如2018.07.09的格式化好的當天日期

創建Date對象，調用SimpleDateFormat對象的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) + 1) + "");  
        System.out.println("日: 
 
" + now.get(Calendar.DAY_OF_MONTH));  
        System.out.println("時: " + 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("當前時間毫秒數：" + 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("格式化後的日期：" + dateNowStr);  
          
        String str = "2012-1-13 17:26:33";  //要跟上面sdf定義的格式一樣  
        Date today = sdf.parse(str);  
        System.out.println("字符串轉成日期：" + today);  
    }  
}  

輸出結果：

年: 2012
月: 1
日: 13
時: 17
分: 28
秒: 19
當前時間毫秒數：1326446899902
Fri Jan 13 17:28:19 CST 2012
Fri Jan 13 17:28:19 CST 2012
格式化後的日期：2012-01-13 17:28:19
字符串轉成日期：Fri Jan 13 17:26:33 CST 2012

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

java 日期的格式化 輸入/輸出