Stream流常用写法

List<User> list = new ArrayList<User>();
list =  Arrays.asList(
        new User("小强", 11, "男"),
        new User("小玲", 15, "女"),
        new User("小虎", 23, "男"),
        new User("小雨", 26, "女"),
        new User("小飞", 19, "男"),
        new User("小玲", 15, "女")
);
//分组
Map<String, List<User>> listMap = list.stream().collect(Collectors.groupingBy(User::getSex));
for(String key:listMap.keySet()){
    System.out.print(key+"组:");
    listMap.get(key).forEach(user -> System.out.print(user.getName()));
    System.out.println();
}
//排序
list.stream().sorted(Comparator.comparing(user-> user.getAge()))
        .forEach(user -> System.out.println(user.getName()));


//过滤
list.stream().filter(user -> user.getSex().equals("男")).collect(Collectors.toList())
        .forEach(user -> System.out.println(user.getName()));
//多条件去重
list.stream().collect(Collectors.collectingAndThen(
        Collectors.toCollection(() -> new TreeSet<>(
                Comparator.comparing(user -> user.getAge() + ";" + user.getName()))), ArrayList::new))
        .forEach(user -> System.out.println(user.getName()));
//最小值
Integer min = list.stream().mapToInt(User::getAge).min().getAsInt();
//最大值
Integer max = list.stream().mapToInt(User::getAge).max().getAsInt();
//平均值
Double average = list.stream().mapToInt(User::getAge).average().getAsDouble();
//和
Integer sum = list.stream().mapToInt(User::getAge).sum();
System.out.println("最小值:"+min+", 最大值"+max+", 平均值:"+average+", 和:"+sum);
//分组求和
Map<String, IntSummaryStatistics> collect = list.stream().collect(Collectors.groupingBy(User::getSex, Collectors.summarizingInt(User::getAge)));
IntSummaryStatistics statistics1 = collect.get("男");
IntSummaryStatistics statistics2 = collect.get("女");
System.out.println(statistics1.getSum());
System.out.println(statistics1.getAverage());
System.out.println(statistics1.getMax());
System.out.println(statistics1.getMin());
System.out.println(statistics1.getCount());
System.out.println(statistics2.getSum());
System.out.println(statistics2.getAverage());
System.out.println(statistics2.getMax());
System.out.println(statistics2.getMin());
System.out.println(statistics2.getCount());

//分组，返回 Map有序
list.stream().collect(Collectors.groupingBy(user-> user.getAge(), LinkedHashMap::new, Collectors.toList()));

//提取list中两个属性值，转为map (v1,v2)->v1 防止key重复报错
Map<String, String> userMap = list.stream().collect(Collectors.toMap(User::getName, User::getSex,(v1,v2)->v1));
System.out.println(JsonUtil.toJson(userMap))
//取出所有名字
List<String> names = list.stream().map(User::getName).collect(Collectors.toList());
System.out.println(JsonUtil.toJson(names))
//根据名字去重
List<User> users=  list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User::getName))), ArrayList::new));
System.out.println(JsonUtil.toJson(users))