将列表转换为 JSON [重复]

Question

我从 DB 收到以下列表，我想将其转换为 JSON：

Employee e1=new Employee(101,"Ha","De","Acr");
Employee e2=new Employee(102,"D ","Forouzan","Mc");
Employee e3=new Employee(102,"Op","Ga","Wi");
Employee e4=new Employee(101,"YUI","HI","EX");

我想改变它，它只是遍历上面收到的列表，对于重复的键（101、102），它使用数组创建一个 jsoobject；

ex: 101 : {["Ha","De","Acr"],["YUI","HI","EX"]}

Answer 1

我尝试了以下一个并得到了预期的结果：

public static void main(String[] args) {

    Employee e1 = new Employee(101, "Ha", "De", "Acr");
    Employee e2 = new Employee(102, "D ", "Forouzan", "Mc");
    Employee e3 = new Employee(102, "Op", "Ga", "Wi");
    Employee e4 = new Employee(101, "YUI", "HI", "EX");

    List<Employee> employeeList1 = new ArrayList<>();
    employeeList1.add(e1);      
    employeeList1.add(e4);

    List<Employee> employeeList2 = new ArrayList<>();
    employeeList2.add(e2);
    employeeList2.add(e3);

    Map<Integer, ArrayList<Employee>> map = new HashMap<Integer, ArrayList<Employee>>();
    // As of now , I have populated the map directly, but you can place some logic here for putting the values here dynamically.
    map.put(101, (ArrayList<Employee>) employeeList1);
    map.put(102, (ArrayList<Employee>) employeeList2);

    ObjectMapper mapper = new ObjectMapper();
    try {
        String json = mapper.writeValueAsString(map);
        System.out.println(json);
    } catch (JsonProcessingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Answer 2

我会尝试回答。

List<Employee> list = //Our employees
Map x = new HashMap();
for(int y = 0; y < list; y++){
  x.put(list[y].value0, new Array(list[y].value1, list[y].value2, list[y].value3));
}
JSONObject json = new JSONObject();
json.putAll( x );

这应该可以满足您的需求！ 试试看，让我知道。

Answer 3

有点不清楚您在问什么，因为您的示例输出不是有效的 JSON。我在这里假设您希望将员工标识符映射到员工列表，您可以使用Map<Integer, List<Employee>> 对其进行建模。要从此数据结构生成 JSON，您需要一个外部库，例如 Jackson JSON 库。

假设以下Employee类

public class Employee {

    private final int id;
    private final String name1;       
    private final String name2;
    private final String name3;

    public Employee(int id, String name1, String name2, String name3) {
        this.id = id;
        this.name1 = name1;
        this.name2 = name2;
        this.name3 = name3;
    }

    public int getId() {
        return id;
    }
    public String getName1() {
        return name1;
    }
    public String getName2() {
        return name2;
    }
    public String getName3() {
        return name3;
    }        
}

和编组代码

Employee e1 = new Employee(101,"Ha","De","Acr");
Employee e2 = new Employee(102,"D ","Forouzan","Mc");
Employee e3 = new Employee(102,"Op","Ga","Wi");
Employee e4 = new Employee(101,"YUI","HI","EX");

Map<Integer, List<Employee>> employees = new HashMap<>();
employees.put(101, Arrays.asList(e1, e4));
employees.put(102, Arrays.asList(e2, e3));

String json = new ObjectMapper().writerWithDefaultPrettyPrinter()
    .writeValueAsString(employees);        
System.out.println(json);

你会得到这个 JSON：

{ “102”：[{ “身份证”：102， “名称1”：“D”， "name2" : "Forouzan", “名称3”：“麦克” }, { “身份证”：102， “name1”：“操作”， "name2" : "嘎", “名称3”：“Wi” }], “101”：[{ “身份证”：101， "name1" : "哈", "name2" : "德", “名称3”：“Acr” }, { “身份证”：101， "name1" : "YUI", "name2" : "你好", “名称3”：“前” }] }

代码所需的 Maven 依赖项：

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-core</artifactId>
  <version>2.9.0</version>
</dependency>
<!-- Jackson databinding; ObjectMapper, JsonNode and related classes are here -->
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.9.0</version>
</dependency>