java日期比较例子等...

数据库中employ表，入职日期，今天日期：

测试代码：

package javademo;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class TimeCompare {
    
    public static void main(String args[]) throws Exception{
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test_demo?user=root&password=root");
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("select * from employ");
        
        while(rs.next()){
            String hireDatestr = rs.getString("hiredate");
            Date hireDate = new SimpleDateFormat("yyyy-MM-dd").parse(hireDatestr);
            System.out.println("(方法一)入职天数： " + compartDay(new Date(), hireDate));
            System.out.println("(方法二)入职天数： " + intervalDays(new Date(), hireDate));
            System.out.println("入职日期距今月数： " + getMonthSpace(hireDate, new Date()));
            System.out.println("入职日期是否超过了2个月：" + afterFewMonth(hireDate, 2));
            System.out.println("入职是否已经有半年：" + afterFewMonth(hireDate, 6));
            System.out.println("入职是否已经有两周：" + afterFewWeek(hireDate, 2));
            
            System.out.println();
        }
        
        rs.close();
        stmt.close();
        conn.close();
    }
    
    //比较入职日期距今是否过了n个月
    public static boolean afterFewMonth(Date hireDate, int n){
        boolean result = false;

        Calendar c = Calendar.getInstance();
        c.add(Calendar.MONTH, n);
        
        if(hireDate.after(c.getTime())){
            result = true;
        }
        
        return result;
    }
    
    //比较入职是否有了n周
    /**
     * Calendar.DATE  : 代表天数
     * Calendar.WEDNESDAY: 代表周数
     * Calendar.MONTH : 代表月数
     * Calendar.YEAR :代表年数
     */
    public static boolean afterFewWeek(Date hireDate, int n){
        boolean result = false;

        Calendar c = Calendar.getInstance();
        c.add(Calendar.WEDNESDAY, n);
        System.out.println("计算"+n+"周后日期：" + c.getTime());
        
        if(hireDate.after(c.getTime())){
            result = true;
        }
        
        return result;
    }
    
    /**
     * 比较两个日期之间相差的月数
     * 只能比较月数，计算的不精确，只是单纯的月数之间的比较
     */
    public static int getMonthSpace(Date start, Date end){
        if(start.after(end)){
            Date temp = start;
            start = end;
            end = temp;
        }
        
        Calendar c = Calendar.getInstance();
        c.setTime(start);
        int year1 = c.get(Calendar.YEAR);
        int month1 = c.get(Calendar.MONTH);
        
        c.setTime(end);
        int year2 = c.get(Calendar.YEAR);
        int month2 = c.get(Calendar.MONTH);
        
        int result;
        if(year1==year2){
            result = month2 - month1;
        }else{
            result = 12*(year2-year1) + month2 - month1;
        }
        
        return result;
    }
    
    /**
     * 比较和今天相差的天数 方法一
     * 用毫秒计算差值
     */
    public static int compartDay(Date date1, Date date2){
        if(date1.after(date2)){
            Date temp = date1;
            date1 = date2;
            date2 = temp;
        }
        long intervalMilli = date2.getTime() - date1.getTime();
        return (int)(intervalMilli/(24*60*60*1000));
    }
    
    /**
     * 比较和今天相差的天数方法二   ----不对，纠正结果见下面!!!!!!
     * 用日历的日来计算差值
     */
    public static int intervalDays(Date date1, Date date2){
        if(date1.after(date2)){
            Date temp = date1;
            date1 = date2;
            date2 = temp;
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date1);
        int day1 = calendar.get(Calendar.DAY_OF_YEAR);
        calendar.setTime(date2);
        int day2 = calendar.get(Calendar.DAY_OF_YEAR);
        return day2 - day1;
    }
}

控制台打印：

纠正：比较和今天相差的天数方法二  这个计算方法不对。更新如下：

上面的方法中，如果不是同一个年份的，计算的结果就不对，参考博客：https://blog.csdn.net/ZeroBz/article/details/80757391

代码如下：

package com.cy.test.date;

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

public class TestDate2 {

    public static void main(String[] args) throws ParseException {
        String str = "2010-08-19 14:20:00";
        SimpleDateFormat s = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        Date date1 = s.parse(str);
        Date date2 = new Date();

        System.out.println(intervalDays1(date1, date2));
        System.out.println(intervalDays2(date1, date2));
    }

    /**
     * 方法一
     * 计算两个日期的天数之差 这里默认date1<date2，date精确到时分秒
     * 使用日历的日来计算差值
     * @param date1
     * @param date2
     * @return
     */
    public static int intervalDays1(Date date1, Date date2){
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date1);
        int day1 = calendar.get(Calendar.DAY_OF_YEAR);
        int year1 = calendar.get(Calendar.YEAR);

        calendar.setTime(date2);
        int day2 = calendar.get(Calendar.DAY_OF_YEAR);
        int year2 = calendar.get(Calendar.YEAR);

        if (year1 != year2) {   //不同年
            int timeDistance = 0;
            for (int i = year1; i < year2; i++) {
                if (i % 4 == 0 && i % 100 != 0 || i % 400 == 0) {  //闰年
                    timeDistance += 366;
                }else{  //平年
                    timeDistance += 365;
                }
            }
            return timeDistance + (day2 - day1);
        }else{
            return day2 - day1;
        }
    }

    /**
     * 方法二
     * 计算两个日期的天数之差 这里默认date1<date2，date精确到时分秒
     * 使用SimpleDateFormat将时分秒的日期转化为只有年月日，再利用毫秒计算差值
     * @param date1
     * @param date2
     * @return
     */
    public static int intervalDays2(Date date1, Date date2){
        SimpleDateFormat s = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date day1 = s.parse(s.format(date1));
            Date day2 = s.parse(s.format(date2));
            int intervalDay = (int) ((day2.getTime() - day1.getTime()) / (1000 * 60 * 60 * 24));
            return intervalDay;
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("calculateTkDay，parseException");
        }
        return 0;
    }

}

console打印结果计算结果相同：

3289
3289