对一个集合的元素执行操作并迭代结果以执行其他操作 [英] Performing an operation over the elements of one collection and iterating over the result to perform some other operation

问题描述

如果我有2个收藏品，

List<String> domainArr;
List<Person> personArr;

我想对字符串中的每个元素进行一次小的转换然后迭代personArr to

I would like to make a minor transformation on each of the elements in the String and then iterate over the personArr to

List<String> urlArr = strArr.stream()
    .map(str -> "https://" + strArr)
    .collect(Collectors.toList());

我的方法类似于

List<Person> getPersons(String url){
 /*makes a restful call to the url and gets a List of objects for each URL.*/
}

我想迭代来自urlArr的每个url并将其传递给getPersons（url）方法，并且对于每个获得的结果（List），我我想迭代这个人并对这些人进行更多操作，比如

I would like to iterate over each of the urls from urlArr and pass it to the getPersons(url) method and for each of the obtained result (a List), I would like to iterate over the person and perform more operations on the persons like

persons.stream()
     .filter(Objects::nonNull)
     .map(Person::getName)
     .filter(Objects::nonNull)
     .collect(Collectors.toList());

我希望在所有结果中都包含所有人名。

I am hoping to have all the person names here from all the results.

我想知道如何在Java 8中实现这一功能。任何指针？

I was wondering how to do this the functional way in Java 8. Any pointers?

推荐答案

您可以使用 flatMap 将 List< T> 的流转换为的平流T

You can use flatMap to convert your stream of List<T> into flat stream of T

strArr.stream()
    .map(str -> "https://" + strArr)
    .map(url -> getPersons(url))
    .flatMap(persons -> persons.stream())
    .filter(Objects::nonNull)
    .map(Person::getName)
    .filter(Objects::nonNull)
    .collect(Collectors.toList());

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