如何使用Java 8将LinkedHashMap列表转换为自定义对象列表

Question

我们如何转换列表

示例：列表

这里的名称和名称都是LinkedHashmap键。如果你在IDE中复制下面的片段，你可以更好地理解这个列表

List<LinkedHashMap> list = new ArrayList<>();
LinkedHashMap<String, String> linkedHashMap1 = new LinkedHashMap<>((Map.of("name","David", "designation","Senior Software Engineer")));
LinkedHashMap<String, String> linkedHashMap2 = new LinkedHashMap<>((Map.of("name","Alex", "designation","Software Engineer")));
LinkedHashMap<String, String> linkedHashMap3 = new LinkedHashMap<>((Map.of("name","Jessi","designation","Lead")));
LinkedHashMap<String, String> linkedHashMap4 = new LinkedHashMap<>((Map.of("name","Martin","designation","Manager")));

list.add(linkedHashMap1);
list.add(linkedHashMap2);
list.add(linkedHashMap3);
list.add(linkedHashMap4);
System.out.println(list);

需要转换以上列表

Class Employee {
String name;
String designation;
}

预期输出：

[Employee(name = David, designation = Senior Software Engineer), 
Employee(name = Alex, designation = Software Engineer), 
Employee(name = Jessi, designation = Lead),
Employee(name = Martin, designation = Manager)]      

Answer 1

使用streams，您可以使用以下代码，前提是Employe类有一个具有此签名的构造函数：public Employe（字符串名称，字符串名称）。

List<Employe> customList= list.stream()
    .flatMap(map -> map.entrySet().stream())
    .map(entry -> new Employe(entry.getKey(), entry.getValue()))
    .toList();

Answer 2

在源列表上创建一个流。并使用映射到键"name"和"指定"的值将列表中的每个映射转换为员工的实例。

public static void main(String[] args) {
    List<Map<String, String>> source = List.of(
            Map.of("name","David", "designation","Senior Software Engineer"),
            Map.of("name","Alex", "designation","Software Engineer"),
            Map.of("name","Jessi","designation","Lead"),
            Map.of("name","Martin","designation","Manager"));

    List<Employee> result = source.stream()
            .map(map -> new Employee(map.get("name"), map.get("designation")))
            .collect(Collectors.toList());

    result.forEach(System.out::println);
}

输出

Employee{name='David', designation='Senior Software Engineer'}
Employee{name='Alex', designation='Software Engineer'}
Employee{name='Jessi', designation='Lead'}
Employee{name='Martin', designation='Manager'}

注：

• 将对象存储为地图不是一种好做法。在您的示例中，没有什么可以帮您避免输入错误，您将得到一个属性值而不是一个null