java8 instant 사용자 정의 포맷 방법

java8 instant 사용자 정의 포맷 방법

package com.github.jdk8;

import java.time.Instant; import java.time.LocalDateTime; import java.time.ZoneId; import java.time.format.DateTimeFormatter; import java.time.temporal.UnsupportedTemporalTypeException;

import org.junit.Rule; import org.junit.Test; import org.junit.rules.ExpectedException;

/** 
 * @see http://stackoverflow.com/questions/25229124/format-instant-to-string
 * @author doctor 
 *
 */ 

public class InstantFormat {

@Rule
public ExpectedException ex = ExpectedException.none();

@Test
public void test_wrong_format() {
    Instant now = Instant.now();
    ex.expect(UnsupportedTemporalTypeException.class);
    String format = DateTimeFormatter.ofPattern("yyyy:MM:dd HH:mm:ss").format(now);
    // java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: YearOfEra
    // at java.time.Instant.getLong(Instant.java:608)
}

/**
 * You can not use DateTimeFormatter to format an instant. Instead you must format it by hand.
 * One way to do this is to convert the Instant to a LocalDateTime
 */
@Test
public void test_right_format() {
    LocalDateTime localDateTime = LocalDateTime.ofInstant(Instant.now(), ZoneId.systemDefault());
    String format = localDateTime.format(DateTimeFormatter.ofPattern("yyyy:MM:dd HH:mm:ss"));
    System.out.println(format);
    }
}