Deserialize json using Java Jackson and based on the root element call different classes that match the Json Object within that root element

Question

我是反序列化的新手，我正在嘗試為我的 class 反序列化復雜的 JSON。 我正在使用Jackson 2.12.1 。 我想知道如何在 map 以下 JSON 結構到我的 class 的多種情況下 Z1D78DC8ED14214E5AEZ24 到不同的根元素

我在類路徑的 Resources 文件夾中有一個 JSON 文件，它是這樣的：

   {
      "Employee":{
         "firstName":"First Name",
         "lastName":"Last Name",
         "department":"Department"
      },
      "Student":{
         "firstName":"Student First Name",
         "lastName":"Student Last Name",            
         "studentID":"1234"
      }
   }

我有 2 個 class 分別用於Employee和Car ，它擴展了Person抽象 class 及其類似的東西：

@Getter
@Setter
public abstract class person{
    private String firstName;
    private String lastName;
}

@Getter
@Setter
@JsonRootName(value = "Employee")
public Employee extends person{
    private String department;
}

@Getter
@Setter
@JsonRootName(value = "Student")
public Student extends person{
    private String studentID;
}

public class MainClass{

     public static void main(String []args){
        String jsonFile = FileUtils.readFileToString(new File("src/main/resources/myFile.json"), "UTF-8");
        final ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
        Employee eventInfo = objectMapper.readValue(jsonFile, Employee.class);

        //This works for Employee but I want to make sure that it works for Student as well based on the ROOT ELEMENT value within the JSON
     }
} 

這適用於Employee但我如何配置它以根據 JSON 中的不同 ROOT ELEMENT 值適用於所有類型？ 我覺得我缺少一些基本的東西有人可以幫助我嗎？

PS：我正在使用來自 Project Lombok 的 @Getter 和 @Setter

Answer 1

我嘗試查看許多示例和 Jackson 的文檔。 我終於能夠讓它工作了。 這只是一個示例，可以用作映射 class 的基礎。 就我而言，我試圖根據映射到不同類的元素來查看存在的元素類型。 因此，這可能無法完全按照您的預期工作，但仍然可以作為參考。

我在這里發布相同的內容，以便將來對某人有所幫助：

如果以下是JSON文件內容：

[
  {
    "isA": "Type1",
    "name": "Test",
    "foo": "val1",
    "foo": "val2",
    "bar": "val3",
    "foo": {
      "myField": "Value1",
      "myField": "value2"
    }
  },
  {
    "isA": "Type2",
    "name": "Test1",
    "foo": "val1",
    "foo": "val2",
    "bar": "val3",
    "foo": {
      "myField": "Value1",
      "myField": "value2"
    }
  }
]


public void xmlConverter(InputStream jsonStream) throws IOException {
    // Get the JSON Factory and parser Object
    final JsonParser jsonParser = new JsonFactory().createParser(jsonStream);
    final ObjectMapper objectMapper = new ObjectMapper();
    jsonParser.setCodec(objectMapper);
    
    // Check the first element is ARRAY if not then invalid JSON throw error
    if (jsonParser.nextToken() != JsonToken.START_ARRAY) {
      throw new IllegalStateException("Expected content to be an array");
    }
    
    jsonParser.nextToken();
    
    // Loop until the end of the events file
    while (jsonParser.nextToken() != JsonToken.END_ARRAY) {

      // Get the node
      final JsonNode jsonNode = jsonParser.readValueAsTree();

      //Check if the JsonNode is valid if not then exit the process
      if (jsonNode == null || jsonNode.isNull()) {
        System.out.println("End Of File");
        break;
      }

      // Get the eventType
      final String eventType = jsonNode.get("isA").asText();

      // Based on eventType call different type of class
      switch (eventType) {
        case "Type1":
          final Type1 type1Info = objectMapper.treeToValue(jsonNode, Type1.class);
          break;
        case "Type2":
          final Type2 type2Info = objectMapper.treeToValue(jsonNode, Type2.class);
          break;
        default:
          System.out.println("JSON event does not match any of event : " + eventType);
          break;
      }
    }
}