Why does my JSON mapper not recognize my object?

问题

public class ResponseList implements Serializable {

    private String sku;

    private String query;

    private List<QAResponse> responses;
    // getter and setter
}

The 2nd class:

public class QAResponse implements Serializable {

    private AnswerLevel answerLevel;

    private double similarity;

    private String question;

    private String dataSource;

    private String answer;

    private String ensembleFlag;

    // getter and setter
}

My JSON (jsonOutput):

{  
   "sku":"4265252",
   "query":"\u8fd9\u6b3e\u662f\u5927\u4e00\u5339\u7684\u5440",
   "QAResponse":[  
      {  
         "answerLevel":"L1",
         "similarity":"1.217891",
         "question":"\u51e0\u5339\u7684",
         "dataSource":"knowledge",
         "ensembleFlag":"YES",
         "answer":"1\u5339\u7684"
      }
}

Then why does my JSON object mapper failed?

ResponseList responseList = null;
if (jsonOutput != null) {
    ObjectMapper mapper = new ObjectMapper();
    try {
        responseList = mapper.readValue(jsonOutput, ResponseList.class);
    } catch (IOException io) {
        LOGGER.error(" json mapping to Java object failed!");
        io.printStackTrace();
    }
}

The error message:

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "QAResponse" (class com.jnlu.qe.model.ResponseList), not marked as ignorable (3 known properties: "query", "responses", "sku"])
 at [Source: (String)"{"sku": "4265252", "query": "\u8fd9\u6b3e\u662f\u5927\u4e00\u5339\u7684\u5440", "QAResponse": [{"answerLevel": "L1", "similarity": "1.217891", "question": "\u51e0\u5339\u7684", "dataSource": "knowledge", "ensembleFlag": "YES", "answer": "1\u5339\u7684"}, {"answerLevel": "L1", "similarity": "1.193976", "question": "\u8fd9\u4e2a\u662f\u51e0\u5339\u7684", "dataSource": "knowledge", "ensembleFlag": "YES", "answer": "\u8fd9\u6b3e\u662f1\u5339\u7684"}, {"answerLevel": "L1", "similarity": "1.179149", ""[truncated 8542 chars]; line: 1, column: 96] (through reference chain: com.jnlu.qe.model.ResponseList["QAResponse"])

Why doesn't the "QAResponse" not recognized?

回答1:

Its throwing exception because in json input "QAResponse" property not exist. If you don't want to change responses into class then add @JsonProperty annotation.

@JsonProperty(value = "QAResponse")
private List<QAResponse> responses;

回答2:

Wrong field name in the ResponseList class, instead:

private List<QAResponse> responses;

it should be:

private List<QAResponse> QAResponse;

However QAResponse.answerLevel field should most likely be a String unless AnswerLevel is an enum.

回答3:

I think that is because in the JSON a property has a name QAResponse but in a class it is a responses. So you must make them to have a same name

来源：https://stackoverflow.com/questions/52936445/why-does-my-json-mapper-not-recognize-my-object

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