使用jackson反序列化json以更正子类类型

Question

将字符串反序列化为对象 ..

ObjectMapper objectMapper = new ObjectMapper();

objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

System.out.println(json); // Output is below

Status status = new ObjectMapper().readValue(json, Status.class);

ProcessingStage s = (ProcessingStage) status.getStages().get(0);

// or

DataStage s = (DataStage) status.getStages().get(0);

产生这些错误..

java.lang.ClassCastException: Stage cannot be cast to ProcessingStage

java.lang.ClassCastException: Stage cannot be cast to DataStage

我如何使用 Jackson 将 的子类反序列Stage化为正确的实例类型？

我期待status.stages包含：[DataStage, DataStage, ProcessingStage]，但看起来它包含：[Stage, Stage, Stage]。

上面的输出System.out.println(json);..

{

  "stages":

  [

    {

      "name":"Pre",

      "order":1,

      "data":

      [

        {

          "id":"0688709c-17be-472a-bf5e-7d7b11bd8ccf"

        }

      ],

    },

    {

      "name":"Processing",

      "order":2,

      "data":

      [

        {

          "id":"ac3ecbb5-2aa6-4faf-b443-391472065219"

        }

      ],

    },

    {

      "name":"Post",

      "order":3,

      "status":"not-started"

    }

  ]

}

Status.java

import java.util.List;

import com.fasterxml.jackson.annotation.JsonProperty;

public class Status {

    @JsonProperty("stages")

    private List<Stage> stages;

    public Status() {}

    public List<Stage> getStages() {

        return stages;

    }

    public void setStages(List<Stage> stages) {

        this.stages = stages;

    }

}

Stage.java

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

import com.fasterxml.jackson.annotation.JsonProperty;

import com.fasterxml.jackson.annotation.JsonSubTypes;

@JsonIgnoreProperties(ignoreUnknown = true)

@JsonSubTypes({

    @JsonSubTypes.Type(value = ProcessingStage.class, name = "ProcessingStage"),

    @JsonSubTypes.Type(value = DataStage.class, name = "DataStage") }

)

Answer 1

您可以尝试先使用 instanceOf 评估对象的类&nbsp;if(status.getStages().get(0) instanceOf ProcessingStage) {&nbsp; ProcessingStage s = (ProcessingStage) status.getStages().get(0);&nbsp;}或评估其他班级DataStage