java list map元素排序Collections.sort() 、list.sort()和list.sort()的Lambda表达式 三种实现

list<map>元素排序两种方法：

1、Collections.sort() 

package me.zhengjie;

import org.springframework.web.bind.annotation.RequestParam;

import java.text.ParseException;
import java.util.*;

public class test {

    /**
     * @param args
     */
    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static void main(String[] args) throws ParseException {
        // TODO Auto-generated method stub
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        Map<String, Object> map1 = new HashMap<String, Object>();
        map1.put("监测时间", "2020-06-06");
        Map<String, Object> map2 = new HashMap<String, Object>();
        map2.put("监测时间", "2020-06-07");
        Map<String, Object> map3 = new HashMap<String, Object>();
        map3.put("监测时间", "2020-06-09");
        list.add(map1);
        list.add(map3);
        list.add(map2);
        //排序前
        for (Map<String, Object> map : list) {

            System.out.println(map.get("监测时间"));
        }
        Collections.sort(list, new Comparator<Map<String, Object>>(){

            public int compare(Map<String, Object> o1, Map<String, Object> o2) {
                String name1 =(String)o1.get("监测时间");//name1是从你list里面拿出来的一个
                String name2= (String)o2.get("监测时间"); //name1是从你list里面拿出来的第二个name
                return name1.compareTo(name2);
            }

        });



        //排序后
        System.out.println("-------------------");
        for (Map<String, Object> map : list) {

            System.out.println(map.get("监测时间"));
        }


    }

}

 执行结果：（正序）
2020-06-06
2020-06-09
2020-06-07
-------------------
2020-06-06
2020-06-07
2020-06-09

 

2、list.sort()

package me.zhengjie;

import org.springframework.web.bind.annotation.RequestParam;

import java.text.ParseException;
import java.util.*;

public class test {

    /**
     * @param args
     */
    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static void main(String[] args) throws ParseException {
        // TODO Auto-generated method stub
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        Map<String, Object> map1 = new HashMap<String, Object>();
        map1.put("监测时间", "2020-06-06");
        Map<String, Object> map2 = new HashMap<String, Object>();
        map2.put("监测时间", "2020-06-07");
        Map<String, Object> map3 = new HashMap<String, Object>();
        map3.put("监测时间", "2020-06-09");
        list.add(map1);
        list.add(map3);
        list.add(map2);
        //排序前
        for (Map<String, Object> map : list) {

            System.out.println(map.get("监测时间"));
        }

        list.sort(new Comparator<Map<String, Object>>() {
            public int compare(Map<String, Object> o1, Map<String, Object> o2){
                String i1 =  (String)o1.get("监测时间");
                String i2 =  (String)o2.get("监测时间");
                return i2.compareTo(i1);
            }
        });


        //排序后
        System.out.println("-------------------");
        for (Map<String, Object> map : list) {

            System.out.println(map.get("监测时间"));
        }


    }

}

执行结果：（倒序）

2020-06-06
2020-06-09
2020-06-07
-------------------
2020-06-09
2020-06-07
2020-06-06

3、list.sort() Lambda表达式

list.sort((o1,o2)->((String)o2.get("监测时间")).compareTo((String)o1.get("监测时间")));

package me.zhengjie;

import org.springframework.web.bind.annotation.RequestParam;

import java.text.ParseException;
import java.util.*;

public class test {

    /**
     * @param args
     */
    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static void main(String[] args) throws ParseException {
        // TODO Auto-generated method stub
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        Map<String, Object> map1 = new HashMap<String, Object>();
        map1.put("监测时间", "2020-06-06");
        Map<String, Object> map2 = new HashMap<String, Object>();
        map2.put("监测时间", "2020-06-07");
        Map<String, Object> map3 = new HashMap<String, Object>();
        map3.put("监测时间", "2020-06-09");
        list.add(map1);
        list.add(map3);
        list.add(map2);
        //排序前
        for (Map<String, Object> map : list) {

            System.out.println(map.get("监测时间"));
        }

        list.sort((o1,o2)->((String)o2.get("监测时间")).compareTo((String)o1.get("监测时间")));


        //排序后
        System.out.println("-------------------");
        for (Map<String, Object> map : list) {

            System.out.println(map.get("监测时间"));
        }


    }

}

执行结果同上