JAVA 獲取當前時間

package com.java2nb.novel.core.utils;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

/**
 * 日期工具
 * @author cd
 */
public class DateUtil {

    public static final String DATE_PATTERN = "yyyy-MM-dd";
    public static final String DATE_TIME_PATTERN = "yyyy-MM-dd HH:mm:ss";
    public static final String TIME_PATTERN = "HH:mm:ss";
    public static final String TIME_LONG = "yyyyMMddHHmmss";

    /**
     * 获取昨天的日期时间
     * */
    public static Date getYesterday(){
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.DATE, -1);
        return calendar.getTime();
    }

    /**
     * 根据日期，获取当天开始时间
     * */
    public static Date getDateStartTime(Date date){
        Calendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        /*
        * Calendar.HOUR_OF_DAY:是指获取24小时制的小时,取值范围:0-23;
        * Calendar.HOUR:是指获取12小时制的小时,取值范围:0-12,凌晨和中午都是0,不是12;
        * 需要配合Calendar.AM_PM使用;
        * */
        calendar.set(Calendar.HOUR_OF_DAY,0);
        calendar.set(Calendar.MINUTE,0);
        calendar.set(Calendar.SECOND,0);
        calendar.set(Calendar.MILLISECOND,0);
        return calendar.getTime();
    }

    /**
     * 根据日期，获取当天结束时间
     * */
    public static Date getDateEndTime(Date date){
        Calendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.set(Calendar.HOUR_OF_DAY,23);
        calendar.set(Calendar.MINUTE,59);
        calendar.set(Calendar.SECOND,59);
        calendar.set(Calendar.MILLISECOND,999);
        return calendar.getTime();
    }

    /**
     * 获取上个月开始时间
     *
     * @return
     */
    public static Date getLastMonthStartTime(){
        // 获取当前日期
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.YEAR, 0);
        calendar.add(Calendar.MONTH, -1);
        // 设置为1号,当前日期既为本月第一天
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        calendar.set(Calendar.MILLISECOND, 0);

        return calendar.getTime();
    }

    /**
     * 获取上个月结束时间
     *
     * @return
     */
    public static Date getLastMonthEndTime(){
        // 获取当前日期
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.YEAR, 0);
        calendar.add(Calendar.MONTH, -1);
        // 获取当前月最后一天
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        calendar.set(Calendar.HOUR_OF_DAY, 23);
        calendar.set(Calendar.MINUTE, 59);
        calendar.set(Calendar.SECOND, 59);
        calendar.set(Calendar.MILLISECOND, 999);

        return calendar.getTime();
    }

    public static Date getToday(){
          Calendar calendar = Calendar.getInstance();
          calendar.set(Calendar.MILLISECOND, 999);
          return calendar.getTime();
    }
    /**
     * 格式化日期
     * */
    public static String formatDate(Date date,String patten){

        return new SimpleDateFormat(patten).format(date);
    }


    public static void main(String[] args) {

   
        System.out.println(formatDate(getToday(),TIME_LONG));
        System.out.println(formatDate(getYesterday(),DATE_TIME_PATTERN));
        System.out.println(formatDate(getDateStartTime(getYesterday()),DATE_TIME_PATTERN));
        System.out.println(formatDate(getDateEndTime(getYesterday()),DATE_TIME_PATTERN));
        System.out.println(formatDate(getLastMonthStartTime(),DATE_TIME_PATTERN));
        System.out.println(formatDate(getLastMonthEndTime(),DATE_TIME_PATTERN));
    }

    /**
     * 日期转星期
     * 
     * @param datetime "2017-01-01"
     * @return
     */
    public static String dateToWeek() {
        Calendar calendar = Calendar.getInstance();
        //System.out.println(dateToWeek(formatDate(calendar.getTime(),DATE_TIME_PATTERN)));
        SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd");
        String[] weekDays = { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };
        Calendar cal = Calendar.getInstance(); // 获得一个日历
        Date datet = null;
        try {
            datet = f.parse(formatDate(calendar.getTime(),DATE_TIME_PATTERN));
            cal.setTime(datet);
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        int w = cal.get(Calendar.DAY_OF_WEEK) - 1; // 指示一个星期中的某天。
        if (w < 0)
            w = 0;
        return weekDays[w];
    }

}