Map 转 List

例如把 map 的 key , value 分别对应 Person 对象两个属性：

List<Person> list = map.entrySet().stream().sorted(Comparator.comparing(e -> e.getKey()))
        .map(e -> new Person(e.getKey(), e.getValue())).collect(Collectors.toList());

List<Person> list = map.entrySet().stream().sorted(Comparator.comparing(Map.Entry::getValue))
        .map(e -> new Person(e.getKey(), e.getValue())).collect(Collectors.toList());

List<Person> list = map.entrySet().stream().sorted(Map.Entry.comparingByKey())
    .map(e -> new Person(e.getKey(), e.getValue())).collect(Collectors.toList());

以上三种方式不同之处在于排序的处理。参考链接：

https://www.concretepage.com/java/jdk-8/java-8-convert-map-to-list-using-collectors-tolist-example

List 转 List

List<Employee> employees = persons.stream()
    .filter(p -> p.getLastName().equals("l1"))
    .map(p -> new Employee(p.getName(), p.getLastName(), 1000))
    .collect(Collectors.toList());

List 条件过滤

User match = users.stream().filter((user) -> user.getId() == 1).findAny().get();

List 转 Map

Map<Integer, String> result = list.stream().collect(Collectors.toMap(Hosting::getId, Hosting::getName));
Map<Long, User> maps = userList.stream().collect(Collectors.toMap(User::getId, Function.identity(), (key1, key2) -> key2));

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原文链接：https://blog.csdn.net/hgc0907/article/details/80756730