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 list = map.entrySet().stream().sorted(Comparator.comparing(e -> e.getKey()))
 .map(e -> new Person(e.getKey(), e.getValue())).collect(Collectors.toList());
List list = map.entrySet().stream().sorted(Comparator.comparing(Map.Entry::getValue))
 .map(e -> new Person(e.getKey(), e.getValue())).collect(Collectors.toList());
List 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 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 result1 = list.stream().collect(
 Collectors.toMap(Hosting::getId, Hosting::getName));

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