一、JDK8對list的流處理

1. 跟據某個屬性分組OfficeId：

Map<String, List<IncomeSumPojo>> collect = list.stream().collect(Collectors.groupingBy(IncomeSumPojo::getOfficeId));

2. 根據某個屬性分組OfficeId，彙總某個屬性Money：

Map<String, Double> collect = list.stream().collect(Collectors.groupingBy(IncomeSumPojo::getOfficeId,Collectors.summingDouble(IncomeSumPojo::getMoney)));

3. 根據某個屬性新增條件過濾資料：

list = list.stream().filter(u -> !u.getAmount().equals("0.00")).collect(Collectors.toList());

4. 判斷一組物件裡面有沒有屬性值是某個值：

List<Menu> menuList = UserUtils.getMenuList();
boolean add = menuList.stream().anyMatch(m -> "plan:ctPlan:add".equals(m.getPermission()));

5. 取出一組物件的某個屬性組成一個新集合：

List<String> tableNames=list.stream().map(User::getMessage).collect(Collectors.toList());

6. list去重複：

list = list.stream().distinct().collect(Collectors.toList());

例項如下：

package com.security.common.elk;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import
 
 java.util.Map;
import java.util.stream.Collectors;

public class TEST {

    public static void main(String[] args) {

        List<Student> list = new ArrayList<>();

        Student student1 = new Student();
        student1.setAge("12");
        student1.setSex(0);

        Student student2 = new Student();
        student2.setAge("13");
        student2.setSex(2);

        Student student3 = new Student();
        student3.setAge("11");
        student3.setSex(1);

        Student student4 = new Student();
        student4.setAge("18");
        student4.setSex(1);

        Student student5 = new Student();
        student5.setAge("18");
        student5.setSex(0);

        Student student6 = new Student();
        student6.setAge("18");
        student6.setSex(2);

        Student student7 = new Student();
        student7.setAge("18");
        student7.setSex(2);

        list.add(student1);

        list.add(student2);

        list.add(student3);

        list.add(student4);

        list.add(student5);

        list.add(student6);

        list.add(student7);

        List<Demo> demos = new ArrayList();

        // 原始資料
        System.out.println("原始資料 組裝list<demo>*******************");

        demos = list.stream().map(student -> new Demo(student.getAge(), student.getSex())).collect(Collectors.toList());

        demos.forEach(demo -> {

            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 只取sex為0

        System.out.println("只取sex為0****************");

        List<Demo> demorm = demos.stream().filter(demo -> demo.getSex() == 0).distinct().collect(Collectors.toList());

        demorm.forEach(demo -> {

            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 篩選年齡大於12歲
        System.out.println("篩選年齡大於12歲的*************");

        List<Demo> demoFilter = demos.stream().filter(demo -> Integer.valueOf(demo.getAge()) > 12).collect(Collectors.toList());

        demoFilter.forEach(demo -> {

            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 排序
        System.out.println("排序******************");
        List<Demo> demoSort = demos.stream().sorted((s1, s2) -> s1.getAge().compareTo(s2.getAge())).collect(Collectors.toList());
        demoSort.forEach(demo -> {
            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 倒序
        System.out.println("倒序****************");

        ArrayList<Demo> demoArray = (ArrayList) demos;

        Comparator<Demo> comparator = (h1, h2) -> h1.getAge().compareTo(h2.getAge());

        demos.sort(comparator.reversed());

        //or
        demos.sort(Comparator.comparing(Demo::getAge).reversed());

        demos.forEach(demo -> {

            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 多條件正序
        System.out.println("多條件排序正序****************");

        demoArray.sort(Comparator.comparing(Demo::getSex).thenComparing(Demo::getAge));

        demoArray.forEach(demo -> {

            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 多條件倒序

        System.out.println("多條件排序倒序 sex 倒序****************");

        demoArray.sort(Comparator.comparing(Demo::getSex).reversed().thenComparing(Demo::getAge));

        demoArray.forEach(demo -> {

            System.out.println("年齡 " + demo.getAge() + " 性別 " + demo.getSex() + ",");

        });

        // 按照年齡分組

        System.out.println("根據age分組結果為Map****************");

        Map demoOder = demos.stream().collect(Collectors.groupingBy(Demo::getAge));

        System.out.println(demoOder);

    }

}

class Demo {

    private String name;

    private Integer sex;

    private String age;

    public Demo(String age, Integer sex) {

        this.age = age;

        this.sex = sex;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Integer getSex() {

        return sex;

    }

    public void setSex(Integer sex) {

        this.sex = sex;

    }

    public String getAge() {

        return age;

    }

    public void setAge(String age) {

        this.age = age;

    }

}

class Student {

    private String age;

    private Integer sex;

    public String getAge() {

        return age;

    }

    public void setAge(String age) {

        this.age = age;

    }

    public Integer getSex() {

        return sex;

    }

    public void setSex(Integer sex) {

        this.sex = sex;

    }

}