java - 转换地图> 到地图>，使用 Java 8 流。我这样做了，但是没有 for 循环怎么做

Question

代码中的 for 循环需要替换为 java8 流。我该如何解决这个问题？

public class Conversion {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        //Person class (name, age , gender)
        //Employee class (name, gender)
        Map<String, List<Person>> mapPerson = new HashMap<String, List<Person>>();
        Map<String, List<Employee>> employeeMap = new HashMap<>();

        List<Person> personList1 = new ArrayList<Person>();
        personList1.add(new Person("Adam", 22, "Male"));
        personList1.add(new Person("Alon", 21, "Female"));

        List<Person> personList2 = new ArrayList<Person>();
        personList2.add(new Person("Chad", 23, "Male"));
        personList2.add(new Person("Daina", 21, "Female"));

        List<Person> personList3 = new ArrayList<Person>();
        personList3.add(new Person("Mark", 22, "Female"));
        personList3.add(new Person("Helen", 25, "Male"));

        mapPerson.put("A", personList1);
        mapPerson.put("B", personList2);
        mapPerson.put("C", personList3);

        for (Map.Entry<String, List<Person>> entry : mapPerson.entrySet()) {
            String key = entry.getKey();
            List<Person> values = entry.getValue();
            System.out.println("Key = " + key);
            System.out.println("Values = " + values + "n");
        }
        System.out.println("******************************************");
        employeeMap = getEmployeeMap(mapPerson);

        for(Map.Entry<String, List<Employee>> listMap : employeeMap.entrySet())
        {
            System.out.println("Key : " + listMap.getKey());
            System.out.println("Values : " + listMap.getValue());
            System.out.println("===============");
        }
    }

这是 MAP 迭代函数中的 for 循环。而不是这个，我必须使用流。

    public static Map<String, List<Employee>> getEmployeeMap(Map<String, List<Person>> personMap) {

        Map<String, List<Employee>> employeeMap = new HashMap<>();

        for(Map.Entry<String, List<Person>> listMap : personMap.entrySet()) {
            String key = listMap.getKey();
            List<Person> personList = listMap.getValue();   
            List<Employee> employeeList = personList.stream().map(p-> new Employee(p.getName(), p.getGender())).collect(Collectors.toList());

            employeeMap.put(key, employeeList);
        }       
        return employeeMap;
    }   
}

标签： javajava-8java-stream

Answer 1

您可以使用Collectors.toMap和修改其中的值。

Map<String, List<Employee>> employeeMap =
    mapPerson.entrySet().stream()
   .collect(Collectors.toMap(Map.Entry::getKey,
        e -> e.getValue().stream().map(p-> new Employee(p.getName(), p.getGender())).collect(Collectors.toList()));