需求： 需要对List中的每个student对象按照birthday顺序排序，时间由小到大排列。

1. 刚开始用的是冒泡排序，出现数据覆盖的情况

for (int i = 0; i < list.size() - 1; i++) {for (int j = 0; j < list.size() - 1 - i; j++) {long time = list.get(j).getCreateAt().getTime();long time1 = list.get(j + 1).getCreateAt().getTime();if (time >time1) {tObject temp = list.get(j+1);BeanUtils.copyProperties(list.get(j), list.get(j+1));BeanUtils.copyProperties(temp, list.get(j));}}

2. 之后想到了Comparator比较器

public static <T> void sort(List<T> list，Comparator<? super T> )

这个里面就涉及到了Comparator 这个接口，位于位于java.util包下，排序是comparator能实现的功能之一,通俗地讲需要比较两个对象 谁排在前谁排在后，那么比较的方法就是：

• public int compare(String o1, String o2)：比较其两个参数的顺序

两个对象比较的结果有三种：大于，等于，小于。 
如果要按照升序排序， 则o1 小于o2，返回（负数），相等返回0，01大于02返回（正数） 
如果要按照降序排序 则o1 小于o2，返回（正数），相等返回0，01大于02返回（负数）

操作如下

package com.hbsi.test;import java.text.SimpleDateFormat;
import java.util.*;public class ListSort {static class Student {private String userName;private String birthday;public Student() {}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getBirthday() {return birthday;}public void setBirthday(String birthday) {this.birthday = birthday;}@Overridepublic String toString() {return "Student{" +"userName='" + userName + '\'' +", birthday='" + birthday + '\'' +'}';}}public static void main(String[] args) {Student s1 = new Student();Student s2 = new Student();Student s3 = new Student();List<Student> list = new ArrayList<Student>();s1.setUserName("aa");s1.setBirthday("1997-01-08");s2.setUserName("bb");s2.setBirthday("1990-11-08");s3.setUserName("cc");s3.setBirthday("1957-05-08");list.add(s1);list.add(s2);list.add(s3);System.out.println("排序前:");for (Student o : list) {System.out.println(o);}listSort(list);System.out.println("排序后:");for (Student o : list) {System.out.println(o);}}private static void listSort(List<Student> list) {Collections.sort(list, new Comparator<Student>() {SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");public int compare(Student o1, Student o2) {try {Date dt1 = sf.parse(o1.getBirthday());Date dt2 = sf.parse(o2.getBirthday());if (dt1.getTime() > dt2.getTime()) {return 1;} else if (dt1.getTime() < dt2.getTime()) {return -1;} else {return 0;}} catch (Exception e) {e.printStackTrace();}return 0;}});}
}

List集合, 时间正序排列、倒序排序

public class Test {public static void main(String[] args) {//MySQL识别的日期格式String str01 = "2021-06-26T12:11:52.000+0000";String str02 = "2021-06-25T12:08:41.000+0000";String str03 = "2021-06-27T12:18:22.000+0000";Student student01 = new Student(1, "张三", dealDateFormat(str01));Student student02 = new Student(2, "李四", dealDateFormat(str02));Student student03 = new Student(3, "王五", dealDateFormat(str03));List<Student> arrayList = new ArrayList<>();Collections.addAll(arrayList, student01, student02, student03);//TODO:正序排列[最小的时间在前]// 输出: [{"date":"2021-06-25 12:08:41","name":"李四","id":2},// {"date":"2021-06-26 12:11:52","name":"张三","id":1},// {"date":"2021-06-27 12:18:22","name":"王五","id":3}]Collections.sort(arrayList, Comparator.comparing(Student::getDate));System.out.println(JSON.toJSON(arrayList));//TODO:倒序排序[最大的在前]//输出: [{"date":"2021-06-27 12:18:22","name":"王五","id":3},// {"date":"2021-06-26 12:11:52","name":"张三","id":1},// {"date":"2021-06-25 12:08:41","name":"李四","id":2}]        Collections.sort(arrayList, new CalendarComparator());System.out.println(JSON.toJSON(arrayList));}// 时间倒序排序    private static class CalendarComparator implements Comparator {public int compare(Object object1, Object object2) {//实现接口中的方法            Student p1 = (Student) object1; // 强制转换           Student p2 = (Student) object2;return p2.getDate().compareTo(p1.getDate());}}}

 static String dealDateFormat(String oldDate) {Date date1 = null;DateFormat df2 = null;try {DateFormat df = new SimpleDateFormat(ExchangeConstants.FORMAT_T);Date date = df.parse(oldDate);SimpleDateFormat df1 = new SimpleDateFormat(ExchangeConstants.FORMAT_Z, Locale.UK);date1 = df1.parse(date.toString());df2 = new SimpleDateFormat(ExchangeConstants.FORMAT);} catch (Exception e) {e.printStackTrace();}return df2.format(date1);}