Json serialize and deserialize with same name

Question

When I call my API with a request body I deserialize it with the variable name in my POJO. I modify the same list and return back but it duplicates the list

@JsonSerialize
@JsonIgnoreProperties(ignoreUnknown = true)
public class UASchema {

    @JsonProperty("metric_id")
    private ArrayList<String> fMetricId;
    @JsonProperty("schema")
    private ArrayList<String> fSchema;
    @JsonProperty("hash")
    private String fHash;
...
...
//getter and setters
}

Request body is

{
    "data" : [
        {
            "metric_id": ["k1", "ak2", "d90"],
            "schema": ["s1", "s2"]
        },
        {
            "metric_id": ["k21", "k22"],
            "schema": ["a11", "s22"]    
        }
    ]
}

Response I get is (added hash)

{
    "result": [
        {
            "fmetricId": [
                "k1",
                "ak2",
                "d90"
            ],
            "fschema": [
                "s1",
                "s2"
            ],
            "metric_id": [
                "k1",
                "ak2",
                "d90"
            ],
            "schema": [
                "s1",
                "s2"
            ],
            "hash": "389abc9093442cfd2aee1f20807ba467"
        },
        {
            "fmetricId": [
                "k21",
                "k22"
            ],
            "fschema": [
                "a11",
                "s22"
            ],
            "metric_id": [
                "k21",
                "k22"
            ],
            "schema": [
                "a11",
                "s22"
            ],
            "hash": "5f366dde65b69fa679f95a81f3115b7f"
        }
    ]
}

It duplicates the list and not correctly serializing it. I want the response to just have the same list as request body and I added hash back.

Answer 1

It looks like your algorithm duplicates entries or you manually generated getters and setters which duplicate output. By default Jackson does not add extra entries. See below example how you can do that, I generated getters and setters in IDE. f-fieldName pattern for fields is outdated and you should use regular names. See, for example, Google's Java Guide:

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.io.File;
import java.util.List;
import java.util.UUID;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);

        Root root = mapper.readValue(jsonFile, Root.class);
        root.getData().forEach(s -> s.setfHash(UUID.randomUUID().toString()));

        System.out.println(mapper.writeValueAsString(root));
    }
}

class Root {
    private List<UASchema> data;

    public List<UASchema> getData() {
        return data;
    }

    public void setData(List<UASchema> data) {
        this.data = data;
    }

    @Override
    public String toString() {
        return "Root{" +
                "data=" + data +
                '}';
    }
}

class UASchema {

    @JsonProperty("metric_id")
    private List<String> fMetricId;

    @JsonProperty("schema")
    private List<String> fSchema;

    @JsonProperty("hash")
    private String fHash;

    public List<String> getfMetricId() {
        return fMetricId;
    }

    public void setfMetricId(List<String> fMetricId) {
        this.fMetricId = fMetricId;
    }

    public List<String> getfSchema() {
        return fSchema;
    }

    public void setfSchema(List<String> fSchema) {
        this.fSchema = fSchema;
    }

    public String getfHash() {
        return fHash;
    }

    public void setfHash(String fHash) {
        this.fHash = fHash;
    }

    @Override
    public String toString() {
        return "UASchema{" +
                "fMetricId=" + fMetricId +
                ", fSchema=" + fSchema +
                ", fHash='" + fHash + '\'' +
                '}';
    }
}

Above code prints:

{
  "data" : [ {
    "metric_id" : [ "k1", "ak2", "d90" ],
    "schema" : [ "s1", "s2" ],
    "hash" : "80dcf06d-1d83-463c-afb8-edef8efdc71f"
  }, {
    "metric_id" : [ "k21", "k22" ],
    "schema" : [ "a11", "s22" ],
    "hash" : "a83d7981-4b80-4318-a632-f3c91d14379b"
  } ]
}