java8 日期时间处理

之前有个项目频繁用到年、月、周的数据库统计。为此专门写了一个蛮复杂的工具类。最近了解了一下java8的新日期时间类库，简直方便到感人。重构了一下代码，行数少了多一半，有些方法直接删掉了，因为已经自带了。适用多种业务场景：展示、统计、设置有效期、增加/减少日期、日期比较等。

package com.utils.zjc;

import java.time.DayOfWeek;
import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;

public class DateMethod8{

	//把毫秒数转换为标准日期时间字符串
	public String formatMilliSecond(long milliSeconds) {
		ZoneId z=ZoneId.systemDefault();
		Instant instant = Instant.now();
		LocalDateTime datetime = LocalDateTime.ofEpochSecond(milliSeconds/1000, 0,z.getRules().getOffset(instant));
		DateTimeFormatter formatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
		return datetime.format(formatter);
	}

	//获取当前日期时间字符串
	public String getNowDateAndTimeString() {
		LocalDateTime now = LocalDateTime.now();
		DateTimeFormatter formatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
		return now.format(formatter);
	}

	//获取当前日期字符串
	public String getNowDateString() {
		LocalDate today=LocalDate.now();
		return today.toString();
	}

	//获取当前时间字符串
	public String getNowTimeString() {
		LocalTime now = LocalTime.now();
		DateTimeFormatter formatter=DateTimeFormatter.ofPattern("HH:mm:ss");
		return now.format(formatter);
	}

	//获取某年某月第一天
	public String getYearMonthFirstDayString(int year, int month) throws Exception {
		if(month<1||month>12){
			throw new Exception("invalid parameters");
		}
		Integer iyear = Integer.valueOf(year);
		Integer imonth = Integer.valueOf(month);
		if(month<10){
			return iyear.toString()+"-0"+imonth.toString()+"-01 00:00:00";
		}else{
			return iyear.toString()+"-"+imonth.toString()+"-01 00:00:00";
		}
	}

	//获取某年某月最后一天
	public String getYearMonthLastDayString(int year, int month) throws Exception {
		if(month<1||month>12){
			throw new Exception("invalid parameters");
		}
		LocalDate date = LocalDate.of(year,month,1);
		Integer lastday=date.getMonth().length(date.isLeapYear());
		Integer iyear = Integer.valueOf(year);
		Integer imonth = Integer.valueOf(month);
		if(month<10){
			return iyear.toString()+"-0"+imonth.toString()+"-"+lastday.toString()+" 23:59:59";
		}else{
			return iyear.toString()+"-"+imonth.toString()+"-"+lastday.toString()+" 23:59:59";
		}
	}

	//获取某年某月某日所在周的某一天
	public String getWeekDayString(int year, int month, int day, DayOfWeek dow) throws Exception{
		try{
			LocalDate date = LocalDate.of(year,month,day);
			LocalDate newDate = date.with(TemporalAdjusters.nextOrSame(dow));
			return newDate.toString();
		}catch(Exception e){
			throw new Exception("invalid parameters");
		}
	}
	public static void main(String[] args){
		LocalDateTime now = LocalDateTime.now();
		LocalDateTime nextMonth = now.plusMonths(1);  //向后延续一个月
		DateTimeFormatter formatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
		System.out.println(nextMonth.format(formatter));
		int compareResult = nextMonth.compareTo(now); //比较日期和时间
		if(compareResult>0){
			System.out.println("晚于当前");
		}else if(compareResult==0){
			System.out.println("相同");
		}else{
			System.out.println("早于当前");
		};
		LocalDate temp = LocalDate.now();
		System.out.println(temp.with(TemporalAdjusters.lastDayOfMonth()));//月末一天的另一种方法
		Duration dtime = Duration.between(now, nextMonth);  //计算时间间隔
		long seconds = dtime.getSeconds();//秒表示 
		long millis = dtime.toMillis();//毫秒表示
		System.out.println(seconds);
		System.out.println(millis);
		try{
			LocalDate newDate = LocalDate.of(2005,2,28);  //验证日期有效性
			LocalDateTime newTime = LocalDateTime.of(newDate, LocalTime.now());
			System.out.println("日期有效");
			System.out.println(newTime.format(formatter));
		}catch(Exception e){
			System.out.println("日期无效");
		}
	}
}