JDK8通过Stream 对List，Map操作和互转的实现

1、Map数据转换为自定义对象的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

2、List对象转换为其他List对象：

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

3、从List中过滤出一个元素

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

4、List转换为Map

public class Hosting {

private int Id;
private String name;
private long websites;

public Hosting(int id, String name, long websites) {
Id = id;
this.name = name;
this.websites = websites;
}

//getters, setters and toString()
}
Map<Integer, String> result1 = list.stream().collect(
Collectors.toMap(Hosting::getId, Hosting::getName));

以上就是本文的全部内容，希望对大家的学习有所帮助

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