Jackson JSON custom serialization for certain fields

Steve_Kuo_24396 0
Viewed 142097

Is there a way using Jackson JSON Processor to do custom field level serialization? For example, I'd like to have the class

public class Person {
    public String name;
    public int age;
    public int favoriteNumber;
}

serialized to the follow JSON:

{ "name": "Joe", "age": 25, "favoriteNumber": "123" }

Note that age=25 is encoded as a number while favoriteNumber=123 is encoded as a string. Out of the box Jackson marshalls int to a number. In this case I want favoriteNumber to be encoded as a string.

jackson serialization json java
7 Answers

In case you don't want to pollute your model with annotations and want to perform some custom operations, you could use mixins.

ObjectMapper mapper = new ObjectMapper();
SimpleModule simpleModule = new SimpleModule();
simpleModule.setMixInAnnotation(Person.class, PersonMixin.class);
mapper.registerModule(simpleModule);

Override age:

public abstract class PersonMixin {
    @JsonSerialize(using = PersonAgeSerializer.class)
    public String age;
}

Do whatever you need with the age:

public class PersonAgeSerializer extends JsonSerializer<Integer> {
    @Override
    public void serialize(Integer integer, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeString(String.valueOf(integer * 52) + " months");
    }
}
user_15797180

You can create a custom serializer inline in the mixin. Then annotate a field with it. See example below that appends " - something else " to lang field. This is kind of hackish - if your serializer requires something like a repository or anything injected by spring, this is going to be a problem. Probably best to use a custom deserializer/serializer instead of a mixin.

package com.test;

import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.test.Argument;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
//Serialize only fields explicitly mentioned by this mixin.
@JsonAutoDetect(
    fieldVisibility = Visibility.NONE,
    setterVisibility = Visibility.NONE,
    getterVisibility = Visibility.NONE,
    isGetterVisibility = Visibility.NONE,
    creatorVisibility = Visibility.NONE
)
@JsonPropertyOrder({"lang", "name", "value"})
public abstract class V2ArgumentMixin {

  @JsonProperty("name")
  private String name;

  @JsonSerialize(using = LangCustomSerializer.class, as=String.class)
  @JsonProperty("lang")
  private String lang;

  @JsonProperty("value")
  private Object value;


  
  public static class LangCustomSerializer extends JsonSerializer<String> {

    @Override
    public void serialize(String value,
                          JsonGenerator jsonGenerator,
                          SerializerProvider serializerProvider)
        throws IOException, JsonProcessingException {
      jsonGenerator.writeObject(value.toString() + "  - something else");
    }
  }
}
user_27309500
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