Java 流 API 父子关系

Question

我有一个 JSON 文件，表示依赖父 -> 子(主题 -> 短语)。我最初将该 JSON 加载到一个 MyClass 列表中

public class MyClass {

    String subject_name;
    String subject_color;
    Integer subject_weight;
    String phrase_name;
    Integer phrase_weight;      
}

所以最后我会有Collection<MyClass>;

[
  {
    "subject_name": "ADMINISTRATION - Bureaucracy and Org Issues",
    "subject_color": "black",
    "subject_weight": 10,
    "phrase_name": "admin burden"
    "phrase_weight": 1
  },
  {
    "subject_name": "ADMINISTRATION - Bureaucracy and Org Issues",
    "subject_color": "red",
    "subject_weight": 10,
    "phrase_name": "user burden",
    "phrase_weight": 2
  },
  {
    "subject_name": "ADMINISTRATION - Bureaucracy and Org Issues",
    "subject_color": "blue",
    "subject_weight": 10,
    "phrase_name": "client burden",
    "phrase_weight": 3
  },
  {
    "subject_name": "ADMINISTRATION - Data Tools and Systems",
    "subject_color": "white",
    "subject_weight": 10,
    "phrase_name": "Computer level",
    "phrase_weight": 4
  },
  {
    "subject_name": "ADMINISTRATION - Data Tools and Systems",
    "subject_color": "black",
    "subject_weight": 10,
    "phrase_name": "Computer system",
    "phrase_weight": 10
  },
  {
    "subject_name": "ADMINISTRATION - Data Tools and Systems",
    "subject_color": "red",
    "subject_weight": 10,
    "phrase_name": "Computer tools",
    "phrase_weight": 2
  }    
]  

我还有一个类(class):

public Phrase {
    String phrase_name;
    Integer phrase_weight;  
}

public Subject {
    String subject_name;
    String subject_color;
    Integer subject_weight;
    Set<Phrase> phrases;
}

如何使用 Java 8 流最终从 Collection 集合中获取 Subject 对象。我只能选择主题列表，但不确定如何处理短语子集。这是我的代码:

@Test
public void testUploadJSON() throws FileNotFoundException {

    String json = "C:\\ttt\\file.json";

    Gson gson = new Gson();
    BufferedReader br = new BufferedReader(new FileReader(json));
    Type type = new TypeToken<Collection<MyClass>>() {
    }.getType();
    Collection<MyClass> jsonData = gson.fromJson(br, type);

    Set<Subject> subjects = jsonData.stream().map(myClass -> {
        Subject subject = new Subject();
        subject.setName(myClass.getSubjectName());
        subject.setColor(myClass.getSubjectColor());
        subject.setWeight(myClass.getSubjectWeight());
        return subject;
    }).collect(Collectors.toSet());

    System.out.println(subjects.size());

    assertFalse(jsonData.isEmpty());
}

更新 我只是用主题和短语的更多属性更新了输入 JSON 文件。

Answer 1

你可以这样做:

 Map<String, Set<String>> collect = 
 jsonData.stream().collect(Collectors.groupingBy(MyClass::getSubject_name, Collectors.mapping(MyClass::getPhrase_name, Collectors.toSet())));

您必须将 getters 和 setters 添加到您的 MyClass 才能使用 方法引用