java8 Stream新特性

import lombok.Getter;
import lombok.Setter;

@Setter
@Getter
public class Person {
    private String name;  // 姓名
    private int salary; // 薪资
    private int age; // 年龄
    private String sex; //性别
    private String area;  // 地区

    // 构造方法
    public Person(String name, int salary, int age,String sex,String area) {
        this.name = name;
        this.salary = salary;
        this.age = age;
        this.sex = sex;
        this.area = area;
    }
}

import lombok.extern.slf4j.Slf4j;

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

@Slf4j
public class StreamTest {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(7, 6, 9, 3, 8, 2, 1,6,6,8);
        List<Person> personList = new ArrayList<Person>();
        personList.add(new Person("Tom", 8900, 23, "male", "New York"));
        personList.add(new Person("Jack", 7000, 25, "male", "Washington"));
        personList.add(new Person("Lily", 7800, 21, "female", "Washington"));
        personList.add(new Person("Anni", 8200, 24, "female", "New York"));
        personList.add(new Person("Owen", 9500, 25, "male", "New York"));
        personList.add(new Person("Alisa", 7900, 26, "female", "New York"));
        personList.add(new Person("koukay", 9500, 26, "male", "New York"));
        personList.add(new Person("houkay", 7800, 28, "male", "New York"));

        /*maxLength();
        more6Print(list, 6);
        findFirst(list);
        more6(list);
        less6(list);
        more7();
        findPerson(personList);
        maxValue();
        maxSalary(personList);
        more6Count(list);
        upperCaseAdd3();
        addSalary(personList);
        splitList();
        calculate();
        sumAndMax(personList);
        collectTo(list,personList);
        operate(personList);
        group(personList);
        join(personList);
        collectReducing(personList);
        sort(personList);
        */
        distinctAndSkip();

　　　　　listMapOrder();

}

   /**
     * mapList排序
     */
    private static void listMapOrder(){
        List<Map<String,Double>> comments= new ArrayList<>();
        for (int i = 0; i <10; i++) {
            Map<String,Double> map= new HashMap<>();
            map.put("DateStr",Math.random());
            comments.add(map);
        }

        List<Map<String, Double>> collect = comments.stream().sorted(Comparator.comparing(StreamTest::comparingByData)).collect(Collectors.toList());
        for (Map<String, Double> stringObjectMap : collect) {
            System.out.println(stringObjectMap.get("DateStr"));
        }
    }
    private static Double comparingByData(Map<String,Double> map){
        return map.get("DateStr");
    }

/**
     * 流合并、去重、限制、跳过等操作。
     */
    private static void distinctAndSkip(){
        String[] arr1 = { "a", "b", "c", "d" };
        String[] arr2 = { "d", "e", "f", "g" };
        Stream<String> stream1 = Arrays.stream(arr1);
        Stream<String> stream2 = Arrays.stream(arr2);

        // concat:合并两个流 distinct：去重
        List<String> collect1 = Stream.concat(stream1, stream2).distinct().collect(Collectors.toList());

        // limit：限制从流中获得前n个数据
        List<Integer> collect2 = Stream.iterate(1, x -> x + 2).limit(5).collect(Collectors.toList());
        // skip：跳过前n个数据
        List<Integer> collect3 = Stream.iterate(1, x -> x + 2).skip(2).limit(5).collect(Collectors.toList());
        System.out.println("合并去重的结果为: "+collect1);
        System.out.println("取出前五个数据: "+collect2);
        System.out.println("跳过前两个数据: "+collect3);
    }

    /**
     * sorted，中间操作。有两种排序：
     *
     * sorted()：自然排序，流中元素需实现Comparable接口
     * sorted(Comparator com)：Comparator排序器自定义排序
     */
    private static void sort(List<Person> personList){
        // 按工资增序排序
        List<String> collect1 = personList.stream().sorted(Comparator.comparing(Person::getSalary)).map(Person::getName).collect(Collectors.toList());
        // 按工资倒序排序
        List<String> collect2 = personList.stream().sorted(Comparator.comparing(Person::getSalary).reversed()).map(Person::getName).collect(Collectors.toList());
        // 先按工资再按年龄自然排序（从小到大）
        List<String> collect3 = personList.stream().sorted(Comparator.comparing(Person::getSalary).thenComparing(Person::getAge)).map(Person::getName).collect(Collectors.toList());
        // 先按工资再按年龄自定义排序（从大到小）
        List<String> collect4 = personList.stream().sorted((p1, p2) -> {
            if (p1.getSalary() == p2.getSalary()) {
                return p2.getAge() - p1.getAge();
            } else {
                return p2.getSalary() - p1.getSalary();
            }
        }).map(Person::getName).collect(Collectors.toList());
        //先按工资再按年龄倒序
        List<String> collect5 = personList.stream().sorted(Comparator.comparing(Person::getSalary).thenComparing(Person::getAge)).map(Person::getName).collect(Collectors.toList());
        // 先按工资再按年龄自定义排序（从大到小）
        System.out.println("按工资增序排序: "+collect1);
        System.out.println("按工资倒序排序: "+collect2);
        System.out.println("先按工资再按年龄自然排序（从小到大）: "+collect3);
        System.out.println("先按工资再按年龄自定义排序（从大到小）: "+collect4);
        System.out.println("先按工资再按年龄倒序: "+collect5);

    }

    /**
     * Collectors类提供的reducing方法，相比于stream本身的reduce方法，增加了对自定义归约的支持。
     */
    private static void collectReducing(List<Person> personList){
        // 每个员工减去起征点后的薪资之和
        Optional<Integer> reduce = personList.stream().map(p -> p.getSalary() - 5000).reduce(Integer::sum);
        Integer collect = personList.stream().collect(Collectors.reducing(0, Person::getSalary, (x, y) -> (x + y - 5000)));
        System.out.println("员工扣税薪资总和1：" + reduce.get());
        System.out.println("员工扣税薪资总和2：" + collect);

    }

    /**
     * joining可以将stream中的元素用特定的连接符（没有的话，则直接连接）连接成一个字符串。
     */
    private static void join(List<Person> personList){
        String collect = personList.stream().map(Person::getName).collect(Collectors.joining("--"));
        System.out.println("所有成员姓名为: "+collect);
        List<String> list = Arrays.asList("A", "B", "C");
        String collect1 = list.stream().collect(Collectors.joining("*"));
        System.out.println("拼接后的字符串为: "+collect1);
    }

    /**
     * 将员工按薪资是否高于8000分为两部分；将员工按性别和地区分组
     */
    private static void group(List<Person> personList){
        // 将员工按薪资是否高于8000分组
        Map<Boolean, List<Person>> collect = personList.stream().collect(Collectors.partitioningBy(p -> p.getSalary() > 8000));
        Map<Boolean, List<Person>> collect3 = personList.stream().collect(Collectors.groupingBy(p -> p.getSalary() > 8000));
        // 将员工按性别分组
        Map<String, List<Person>> collect1 = personList.stream().collect(Collectors.groupingBy(Person::getSex));
        // 将员工先按性别分组，再按地区分组
        Map<String, Map<String, List<Person>>> collect2 = personList.stream().collect(Collectors.groupingBy(Person::getSex, Collectors.groupingBy(Person::getArea)));
        System.out.println("员工按薪资是否大于8000分组情况：" + collect);
        System.out.println("员工按薪资是否大于8000分组情况：" + collect3);
        System.out.println("员工按性别分组情况：" + collect1);
        System.out.println("员工按性别、地区：" + collect2);
    }

    /**
     * 统计员工人数、平均工资、工资总额、最高工资。
     */
    private static void operate(List<Person> personList){
        //员工人数
        Long collect = personList.stream().collect(Collectors.counting());
        //平均工资
        Double collect1 = personList.stream().collect(Collectors.averagingDouble(p -> p.getSalary()));
        //工资总额
        Double collect2 = personList.stream().collect(Collectors.summingDouble(Person::getSalary));
        //最高工资
        Optional<Integer> collect3 = personList.stream().map(Person::getSalary).collect(Collectors.maxBy(Integer::compare));
        DoubleSummaryStatistics collect4 = personList.stream().collect(Collectors.summarizingDouble(Person::getSalary));
        log.info("员工人数为: {}, 平均工资为: {}, 工资总额为: {}, 最高工资为: {}, 查询工资所有为: {}",collect,collect1,collect2,collect3,collect4);


    }
    private static void collectTo(List<Integer> list, List<Person> personList){
        List<Integer> collect1 = list.stream().filter(x -> x % 2 == 0).collect(Collectors.toList());
        Set<Integer> collect2 = list.stream().filter(x -> x % 2 == 0).collect(Collectors.toSet());
        Map<String, Person> collect = personList.stream().filter(p -> p.getSalary() > 8000).collect(Collectors.toMap(Person::getName, p -> p));
        System.out.println(collect1);
        System.out.println(collect2);
        System.out.println(collect);
    }


    /**
     * 求所有员工的工资之和和最高工资。
     */
    private static void sumAndMax(List<Person> personList){
        //员工工资之和方式一
        Optional<Integer> reduce = personList.stream().map(Person::getSalary).reduce((p1, p2) -> p1 + p2);
        //员工工资之和方式二
        Integer reduce1 = personList.stream().reduce(0, (sum, p) -> sum += p.getSalary(), (sum1, sum2) -> sum1 + sum2);
        //员工工资之和方式三
        Optional<Integer> reduce2 = personList.stream().map(Person::getSalary).reduce(Integer::sum);
        //员工工资之和方式四
        Integer reduce3 = personList.stream().reduce(0, (sum, p) -> sum += p.getSalary(), Integer::sum);

        //员工工资最高值一
        Optional<Integer> reducemax1 = personList.stream().map(Person::getSalary).reduce(Integer::max);
        //员工工资最高值二
        Optional<Integer> reducemax2 = personList.stream().map(Person::getSalary).reduce((s1,s2)->s1>s2?s1:s2);
        //员工工资最高值三
        Integer reduce4 = personList.stream().reduce(0, (max, p) -> max > p.getSalary() ? max : p.getSalary(), Integer::max);
        Integer reduce5 = personList.stream().reduce(0, (max, p) -> max > p.getSalary() ? max : p.getSalary() ,(max1,max2)->max1>max2?max1:max2);
        log.info("员工工资之和1为: {},员工工资之和2为: {},员工工资之和3为: {},员工工资之和4为: {}",reduce.get(),reduce1,reduce2.get(),reduce3);
        log.info("员工工资最高值1: {},员工工资最高值2: {},员工工资最高值3: {},员工工资最高值4: {}",reducemax1.get(),reducemax2.get(),reduce4,reduce5);
    }

    /**
     * 求Integer集合的元素之和、乘积和最大值。
     */
    private static void calculate(){
        List<Integer> list = Arrays.asList(1, 3, 2, 8, 11, 4);
        // 求和方式1
        Optional<Integer> reduce = list.stream().reduce((x, y) -> x + y);
        // 求和方式2
        Optional<Integer> reduce1 = list.stream().reduce(Integer::sum);
        // 求和方式3
        Integer reduce2 = list.stream().reduce(0, Integer::sum);
        log.info("求和方式1: {},  方式2: {},  方式3: {}",reduce.get(),reduce1.get(),reduce2);
        // 求乘积
        Optional<Integer> reduce3 = list.stream().reduce((x, y) -> x * y);
        log.info("求乘积为: {}",reduce3.get());
        // 求最大值方式1
        Optional<Integer> reduce4 = list.stream().reduce((x, y) -> x > y ? x : y);
        // 求最大值方式1
        Optional<Integer> reduce5 = list.stream().reduce(Integer::max);
        log.info("求最大值方法1: {},方式2: {}",reduce4.get(),reduce5.get());
    }

    /**
     * 将两个字符数组合并成一个新的字符数组。
     */
    private static void splitList(){
        List<String> list = Arrays.asList("m,k,l,a", "1,3,5,7");
        List<String> collect = list.stream().flatMap(str -> {
            String[] split = str.split(",");
            return Arrays.stream(split);
        }).collect(Collectors.toList());
        System.out.println(list);
        System.out.println(collect);
    }

    /**
     * 将员工的薪资全部增加1000。
     * @param personList
     */
    private static void addSalary(List<Person> personList){
        List<Person> collect = personList.stream().map((person) -> {
            person.setSalary(person.getSalary() + 1000);
            return person;
        }).collect(Collectors.toList());
        collect.forEach(person -> {
            log.info("{}调薪后的工资为{}",person.getName(),person.getSalary());
        });
    }

    /**
     * 英文字符串数组的元素全部改为大写。整数数组每个元素+3。
     */
    private static void upperCaseAdd3(){
        String[] strArr = { "abcd", "bcdd", "defde", "fTr" };
        List<Integer> intList = Arrays.asList(1, 3, 5, 7, 9, 11);
        List<String> collect1 = Arrays.stream(strArr).map(String::toUpperCase).collect(Collectors.toList());
        List<Integer> collect = intList.stream().map(x -> x + 3).collect(Collectors.toList());

        collect1.forEach(a->{
            log.info("每个元素大写-> "+a);
        });
        collect.forEach(a->{
            log.info("每个元素+3-> "+a);
        });

    }
    private static void more6Count(List<Integer> list){
        long count = list.stream().filter(x -> x > 6).count();
        log.info("大于6的元素有{}个",count);
    }
    private static void maxSalary( List<Person> personList ){
        Optional<Person> max = personList.stream().max(Comparator.comparing(Person::getSalary));
        System.out.println("姓名: "+max.get().getName()+"--------工资 "+max.get().getSalary());
    }
    private static void maxValue(){
        List<Integer> list = Arrays.asList(7, 6, 9, 4, 11, 6);

        //自然排序
        Optional<Integer> max = list.stream().max(Integer::compareTo);
        //自定义排序
        Optional<Integer> max1 = list.stream().max(new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2.compareTo(o1);
            }
        });
        System.out.println("自然排序的最大值：" + max.get());
        System.out.println("自定义排序的最大值：" + max1.get());

    }
    /**
     * 获取String集合中最长的元素
     */
    private static void maxLength(){
        List<String> list = Arrays.asList("adnm", "admmt", "potjhgfdsatfd", "xbangd", "weoujgsd");
        Optional<String> max = list.stream().max(Comparator.comparing(String::length));
        System.out.println(max.get());

    }
    /**
     * 遍历输出符合条件的元素 大于6
     * @param list
     * @param i
     */
    private static void more6Print(List<Integer> list, int i) {
        list.stream().filter(x -> x > i).forEach(System.out::println);
    }

    /**
     *  匹配第一个
     * @param list
     */
    private static void findFirst(List<Integer> list) {
        Optional<Integer> first = list.stream().filter(x -> x > 6).findFirst();
        System.out.println("匹配第一个大于6的数-> "+first.get());
    }

    /**
     * // 匹配任意（适用于并行流）大于6
     * @param list
     */
    private static void more6(List<Integer> list) {
        Optional<Integer> any = list.parallelStream().filter(x -> x > 6).findAny();
        System.out.println("匹配任意（适用于并行流）大于6-> "+any.get());
    }

    /**
     * // 是否包含符合特定条件的元素  小于6
     * @param list
     */
    private static void less6(List<Integer> list) {
        boolean b = list.stream().anyMatch(x -> x < 6);
        System.out.println("是否包含小于6的元素-> "+b);
    }
    /**
     * //筛选出Integer集合中大于7的元素，并打印出来
     */
    private static void more7() {
        List<Integer> list2 = Arrays.asList(6, 7, 3, 8, 1, 2, 9);
        more6Print(list2, 7);
    }

    /**
     * 筛选员工中工资高于8000的人，并形成新的集合
     */
    public static void findPerson(List<Person> personList){

        personList.stream().filter(p -> p.getSalary() > 8000).collect(Collectors.toList()).forEach((t)->{
            System.out.println("姓名: "+t.getName()+"--------工资 "+t.getSalary());
        });
    }
}