如何将平面 JSON 转换为分层 java 类？

Question

我需要将平面 JSON 对象反序列化为 Java 对象，并将一些属性设置为子对象。

{
 "name": "abcd",
 "addressLine1": "123",
 "addressLine2": "1111"
}

---

Class Student {
  String name;
  Address address;
}

Class Address {
 String line1;
 String line2;
}

如何使用 Jackson 将我的 JSON 反序列化为 Student 对象？ 我无法映射addressLine1 to Student.Address.line1 和addressLine2 to Student.Address.line2

Answer 1

编辑：虽然我的解决方案有效，但 Selindek 的答案是最好的

根据https://jsonlint.com/，您的 Json 无效，原因有两个：

• 您的字段名称没有被引用
• 最后一行后面有一个逗号

我将假设这个 JSON，带有不带引号的字段名称：

{
    name: "abcd",
    addressLine1: "123",
    addressLine2: "1111"
}

我可以想到两种方法：

1 - 简单的地图处理

// Create your mapper, and configure it to allow unquoted field names
ObjectMapper mapper = new ObjectMapper();
mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);

// Parse the JSON to a Map
TypeReference<HashMap<String, String>> typeRef
        = new TypeReference<HashMap<String, String>>() {};
Map<String, String> jsonAsMap = null;
try {
    jsonAsMap = mapper.readValue(yourJsonString, typeRef);
} catch (Exception e) {
    System.out.println("Something went wrong:" + e.getMessage());
}


// Read the data from the map and build your objects
Student student = null;
if(jsonAsMap != null) {

    Address address = new Address();
    address.setLine1(jsonAsMap.get("addressLine1"));
    address.setLine2(jsonAsMap.get("addressLine2"));

    student = new Student();
    student.setName(jsonAsMap.get("name"));
    student.setAddress(address);

    System.out.println(student.getName());
    System.out.println(student.getAddress().getLine1());
    System.out.println(student.getAddress().getLine2());
}

2 - 使用代理对象（我更喜欢这个）

另一种方法是拥有一个代理类，您可以在其中反序列化您的 JSON，并从中构建您的学生：

class RawStudent {
    private String name, addressLine1, addressLine2;

    public Student toStudent() {
        Address address = new Address();
        address.setLine1(addressLine1);
        address.setLine2(addressLine2);

        Student student = new Student();
        student.setName(name);
        student.setAddress(address);

        return student;
    }

    // GETTERS / SETTERS

}

并以这种方式使用它：

// Create your mapper, and configure it to allow unquoted field names
ObjectMapper mapper = new ObjectMapper();
mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);

// Parse the JSON to a RawStudent object
RawStudent rawStudent = null;
try {
    rawStudent = mapper.readValue(jsonUnquoted, RawStudent.class);
} catch (Exception e) {
    System.out.println("Something went wrong:" + e.getMessage());
}


// Read the data from the map and build your objects
Student student = null;
if (rawStudent != null) {

    student = rawStudent.toStudent();

    System.out.println(student.getName());
    System.out.println(student.getAddress().getLine1());
    System.out.println(student.getAddress().getLine2());
}

注意

如果您输入错误并且确实有引用的字段，即：

{
    "name": "abcd",
    "addressLine1": "123",
    "addressLine2": "1111"
}

那你就不需要那行了

mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);

Answer 2

你可以这样定义你的数据类：

  public static class Student {
    String name;

    @JsonUnwrapped
    Address address;
  }

  public static class Address {
    @JsonProperty("addressLine1")
    String line1;
    @JsonProperty("addressLine2")
    String line2;
  }

然后您可以按通常的方式使用Objectmapper - 无需任何额外的魔法或解决方法：

Student student = mapper.readValue(json, Student.class);

如果您传入的 json 字符串确实是您提供的格式（不带引号），那么还要添加：

mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);

Answer 3

你可以像这样使用 ObjectMapper：

ObjectMapper objectMapper = new ObjectMapper();
Student student = objectMapper.readValue(json, Student.class);

但您还必须修改 Student 类，并实现所有 getter 和 setter：

Class Student{
    String name;
    String addressLine1;
    String addressLine2;
} 

然后，如果您愿意，可以根据需要将其重构为新类。希望能帮助到你。

Answer 4

首先，确保您的依赖项或库中有jackson-databind。

你可以这样做：

String jsonInput = // You JSON String here;
TypeReference<HashMap<String, String>> typeRef 
  = new TypeReference<HashMap<String, String>>() {};
Map<String, String> map = mapper.readValue(jsonInput, typeRef);

Student student = new Student();
Address address = new Address();

for (Map.Entry<String, String> entry : map.entrySet())
{
    if(((String)entry.getKey()).equals("addressLine1")){
    student.setName(map.get("name"));
    student.setAddress(map.get("addressLine1"));
    }

    if(((String)entry.getKey()).equals("addressLine2")){
    address.setLine1(map.get("addressLine1"));
    address.setLine2(map.get("addressLine2"));
    }
    //System.out.println(entry.getKey() + "/" + entry.getValue());
}

类对象中的直接反序列化意味着类和 Json 字符串具有完全相同的属性。这不是这里的情况。因此使用 for 循环和使用 mutators。

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