/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Locale;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String dateString = "2018-03-20 09:31:31";
 
		DateTimeFormatter formatterForWrongFormat = new DateTimeFormatterBuilder()
				.append(DateTimeFormatter.ISO_LOCAL_DATE)
				.appendLiteral(" ")
				.append(DateTimeFormatter.ISO_LOCAL_TIME)
				.toFormatter();
 
		//1- from String(wrong format) into datetime object
		LocalDateTime dateTime = LocalDateTime.parse(dateString , formatterForWrongFormat);
 
		// 1.1 extract date object (Optional)
		LocalDate myDate =  dateTime.toLocalDate();
 
		// 2- now from your  LocalDateTime to the String in the RIGHT format
		DateTimeFormatter formatterForRightFormat =  DateTimeFormatter.ofPattern("MM/dd/yyyy HH:mm:ss a",
                Locale.ENGLISH);
 
		System.out.println("right format: "+dateTime.format(formatterForRightFormat));
 
	}
}

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