java 将yyyyMMddHHmmss转化为yyyy-MM-dd HH:mm:ss格式的字符串

思路很简单：先转化为yyyyMMddHHmmss格式的Date类型，再格式化为yyyy-MM-dd HH:mm:ss格式的字符串类型

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ConsoleTest {    
    public static void main(String args[]) {        
        String str = "20200402150221";        
        DateFormat df1 = new SimpleDateFormat("yyyyMMddHHmmss");
        DateFormat df2 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        try {
            Date time1 = df1.parse(str);
            String time2 = df2.format(time1);
            System.out.println(time2);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }        
    }
}

jdk1.8

        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMddHHmmss");
        LocalDateTime ldt = LocalDateTime.parse(datetime,dtf);
        DateTimeFormatter fa = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String datetime2 = ldt.format(fa);

jdk1.7

public static String strToDateFormat(String date) throws ParseException{
           SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMddHHmmss");
           formatter.setLenient(false);
           Date newDate= formatter.parse(date);
           formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
           return formatter.format(newDate);
       }