List<User> userList1 = Arrays.asList(
        new User(1, "xw", "男", 22),
        new User(2, "zgx", "男", 22),
        new User(3, "whb", "男", 23),
        new User(4, "gg", "男", 30),
        new User(5, "yda", "男", 22),
        new User(6, "bhm", "女", 23),
        new User(7, "lsn", "女", 22),
        new User(8, "ksj", "女", 22)
);

Integer maxAge1 = userList1.stream().reduce(0, (maxAge, user) -> maxAge > user.getAge() ? maxAge : user.getAge(), Integer::max);
log.info(String.format("年龄最大是：%d", maxAge1));

Optional<Integer> max2 = userList1.stream().map(User::getAge).reduce(Integer::max);
Optional<Integer> max3 = userList1.stream().map(User::getAge).reduce((x, y) -> x > y ? x : y);
log.info(String.format("年龄最大是：%d", max2.get()));
log.info(String.format("年龄最大是：%d", max3.get()));

Integer stringMaxLength = userList1.stream()
        .filter(user -> user.getAge() > 22 && user.getAge() < 25)
        .flatMap(user -> {
            Stream<String> newStream = Arrays.stream(user.toString().split("="));
            return newStream;
        })
        .collect(Collectors.toList())
        .stream().map(String::toUpperCase)
        .reduce(0, (maxLength, string) -> maxLength > string.length() ? maxLength : string.length(), Integer::max);

log.info(String.format("最大字符串长度为：%s", stringMaxLength));

6.收集(collect)

collect，收集，可以说是内容最繁多、功能最丰富的部分了。从字面上去理解，就是把一个流收集起来，最终可以是收集成一个值也可以收集成一个新的集合。

collect主要依赖java.util.stream.Collectors类内置的静态方法。

6.1归集(toList/toSet/toMap)

因为流不存储数据，那么在流中的数据完成处理后，需要将流中的数据重新归集到新的集合里。toList、toSet和toMap比较常用，另外还有toCollection、toConcurrentMap等复杂一些的用法。

toList

List<Integer> list1 = Arrays.asList(1, 2, 8, 0, 9, 0, 1, 23, 32, 37, 49, 48);
List<Integer> collect1 = list1.stream().filter(value -> value > 5).collect(Collectors.toList());
log.info(String.format("list1中收集>5的结果为：%s", collect1));

toSet

Set<Integer> collect2 = list1.stream().filter(value -> value < 5).collect(Collectors.toSet());
log.info(String.format("list1中收集<5的结果为：%s", collect2));
collect2.forEach(value -> {System.out.print(value + " ");

toMap

List<User> userList1 = Arrays.asList(
        new User(1, "xww", "男", 22),
        new User(2, "zgx", "男", 22),
        new User(3, "whb", "男", 23),
        new User(4, "gg", "男", 30),
        new User(5, "yda", "男", 22),
        new User(6, "bhm", "女", 23),
        new User(7, "lsn", "女", 22),
        new User(8, "ksj", "女", 22)
);

Map<String, User> userMap = userList1.stream()
         .filter(user -> user.getSex().equals("女"))
         .collect(Collectors.toMap(User::getName, user -> user));
log.info(String.format("性别为女的用户转map：%s", userMap));

6.2 统计(count/averaging)

Collectors提供了一系列用于数据统计的静态方法：