java 工具类 对比时间 格式转型DateUtil

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


public class DateUtils {
    
    public static final SimpleDateFormat TIME_FORMAT = 
            new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    public static final SimpleDateFormat DATE_FORMAT = 
            new SimpleDateFormat("yyyy-MM-dd");
    
    
    public static boolean before(String time1, String time2) {
        try {
            Date dateTime1 = TIME_FORMAT.parse(time1);
            Date dateTime2 = TIME_FORMAT.parse(time2);
            
            if(dateTime1.before(dateTime2)) {
                return true;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }
    
    
    public static boolean after(String time1, String time2) {
        try {
            Date dateTime1 = TIME_FORMAT.parse(time1);
            Date dateTime2 = TIME_FORMAT.parse(time2);
            
            if(dateTime1.after(dateTime2)) {
                return true;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }
    
    
    public static int minus(String time1, String time2) {
        try {
            Date datetime1 = TIME_FORMAT.parse(time1);
            Date datetime2 = TIME_FORMAT.parse(time2);
            
            long millisecond = datetime1.getTime() - datetime2.getTime();
            
            return Integer.valueOf(String.valueOf(millisecond / 1000));  
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 0;
    }
    
    
    public static String getDateHour(String datetime) {
        String date = datetime.split(" ")[0];
        String hourMinuteSecond = datetime.split(" ")[1];
        String hour = hourMinuteSecond.split(":")[0];
        return date + "_" + hour;
    }  
    
    
    public static String getTodayDate() {
        return DATE_FORMAT.format(new Date());  
    }
    
    
    public static String getYesterdayDate() {
        Calendar cal = Calendar.getInstance();
        cal.setTime(new Date());  
        cal.add(Calendar.DAY_OF_YEAR, -1);  
        
        Date date = cal.getTime();
        
        return DATE_FORMAT.format(date);
    }
    
    
    public static String formatDate(Date date) {
        return DATE_FORMAT.format(date);
    }
    
    
    public static String formatTime(Date date) {
        return TIME_FORMAT.format(date);
    }
    
}







获取某个月第一天的00：00：00

public static void main(String[] args) {
	        Date data = null;
	        try {
	            data = new SimpleDateFormat("yyyy-MM").parse("2020-6");
	        } catch (ParseException e) {
	            e.printStackTrace();
	        }
	        Calendar c = Calendar.getInstance();
	        c.setTime(data);
	        //设置为1号,当前日期既为本月第一天
	        c.set(Calendar.DAY_OF_MONTH, 1);
	        //将小时至0
	        c.set(Calendar.HOUR_OF_DAY, 0);
	        //将分钟至0
	        c.set(Calendar.MINUTE, 0);
	        //将秒至0
	        c.set(Calendar.SECOND,0);
	        //将毫秒至0
	        c.set(Calendar.MILLISECOND, 0);
	        // 本月第一天的时间戳转换为字符串
	        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
	        Date date;
	        try {
	            date = sdf.parse(sdf.format(new Date(new Long(c.getTimeInMillis()))));
	            //Date date = sdf.parse(sdf.format(new Long(s)));// 等价于
	            System.out.println( sdf.format(date));
	        } catch (NumberFormatException e) {
	            // TODO 自动生成的 catch 块
	            e.printStackTrace();
	        } catch (ParseException e) {
	            // TODO 自动生成的 catch 块
	            e.printStackTrace();
	        }
	}




    public static void main(String[] args) {
    	Calendar calendar = new GregorianCalendar();
    	SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    
        Date date = new Date();
        System.out.println(df.format(date));
        calendar.setTime(date);
        calendar.add(GregorianCalendar.YEAR, 1);//把日期往后增加一年.整数往后推,负数往前移动
        calendar.add(GregorianCalendar.DAY_OF_MONTH, 1);//把日期往后增加一个月.整数往后推,负数往前移动
        calendar.add(GregorianCalendar.DATE,1);//把日期往后增加一天.整数往后推,负数往前移动
        calendar.add(GregorianCalendar.WEEK_OF_MONTH, 1);//把日往后增加一个周.整数往后推,负数往前移动
        date=calendar.getTime();   //结果
        System.out.println(df.format(date));
       
       
       
	}