Serializing enums with Jackson

Question

I have an Enum desrcibed below:

public enum OrderType {

  UNKNOWN(0, "Undefined"),
  TYPEA(1, "Type A"),
  TYPEB(2, "Type B"),
  TYPEC(3, "Type C");

  private Integer id;
  private String name;

  private WorkOrderType(Integer id, String name) {
    this.id = id;
    this.name = name;
  }

  //Setters, getters....
}

I return enum array with my controller ( new OrderType[] {UNKNOWN,TYPEA,TYPEB,TYPEC};), and Spring serializes it into the following json string:

["UNKNOWN", "TYPEA", "TYPEB", "TYPEC"]

What is the best approach to force Jackson to serialize enums just like POJOs? E.g.:

[
  {"id": 1, "name": "Undefined"},
  {"id": 2, "name": "Type A"},
  {"id": 3, "name": "Type B"},
  {"id": 4, "name": "Type C"}
]

I played with different annotations but couldn't manage to get such result.

Looks like you already found the solution; great! Was curious as to why you need it? — StaxMan, Oct 15 '11 at 17:25
I'm developing a GWT application which communicates with server-side via JSON. This enum will provide option values for the combobox. — Nofate, Oct 15 '11 at 18:00
Ah ok. So kind of short-hand for set of values... interesting. — StaxMan, Oct 16 '11 at 05:18

score 87 · Accepted Answer · edited Dec 04 '17 at 07:12

87

Finally I found solution myself.

I had to annotate enum with @JsonSerialize(using = OrderTypeSerializer.class) and implement custom serializer:

public class OrderTypeSerializer extends JsonSerializer<OrderType> {

  @Override
  public void serialize(OrderType value, JsonGenerator generator,
            SerializerProvider provider) throws IOException,
            JsonProcessingException {

    generator.writeStartObject();
    generator.writeFieldName("id");
    generator.writeNumber(value.getId());
    generator.writeFieldName("name");
    generator.writeString(value.getName());
    generator.writeEndObject();
  }
}

edited Dec 04 '17 at 07:12

rjdkolb

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answered Oct 14 '11 at 13:35

Nofate

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4

Note that to configure Jackson to use custom (de)serialization processing, an alternative to using an annotation is to register (de)serializers with a configuration module. http://wiki.fasterxml.com/JacksonHowToCustomSerializers – Programmer Bruce Nov 25 '11 at 08:16
1

This did not work for me using Spring 3.1.1. My @Controller still returns json without my attributes. – Dave May 02 '14 at 15:30
I have Some Enums, And I want to get All enums with one function. How can I do it? – Morteza Malvandi Dec 16 '15 at 06:37
For one enum type, I have to define a custom deserializer. Is there any generic solution? – Chao Dec 21 '16 at 05:34

score 83 · Answer 2 · edited Jan 02 '18 at 14:14

83

@JsonFormat(shape= JsonFormat.Shape.OBJECT)
public enum SomeEnum

available since https://github.com/FasterXML/jackson-databind/issues/24

just tested it works with version 2.1.2

answer to TheZuck:

I tried your example, got Json:

{"events":[{"type":"ADMIN"}]}

My code:

@RequestMapping(value = "/getEvent") @ResponseBody
  public EventContainer getEvent() {
    EventContainer cont = new EventContainer();
    cont.setEvents(Event.values());
    return cont;
 }

class EventContainer implements Serializable {

  private Event[] events;

  public Event[] getEvents() {
    return events;
 }

 public void setEvents(Event[] events) {
   this.events = events;
 }
}

and dependencies are:

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-annotations</artifactId>
  <version>${jackson.version}</version>
</dependency>

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-core</artifactId>
  <version>${jackson.version}</version>
</dependency>

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>${jackson.version}</version>
  <exclusions>
    <exclusion>
      <artifactId>jackson-annotations</artifactId>
      <groupId>com.fasterxml.jackson.core</groupId>
    </exclusion>
    <exclusion>
      <artifactId>jackson-core</artifactId>
      <groupId>com.fasterxml.jackson.core</groupId>
    </exclusion>
  </exclusions>
</dependency>

<jackson.version>2.1.2</jackson.version>

edited Jan 02 '18 at 14:14

Rao

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answered Jan 08 '13 at 20:27

Vecnas

1,387
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2

I like this alternative, it's cleaner, however, I tried it with this class and type does not get serialized, any idea what's wrong? @JsonFormat(shape= JsonFormat.Shape.OBJECT) @JsonAutoDetect() public enum Event { VISIT_WEBSITE(Type.ADMIN); @JsonProperty public Type type; public Type getType() { return type; } Event(Type type) { this.type = type; } public enum Type { ADMIN, CONSUMER, } } I'm using Jackson 2.1.2 – TheZuck Jan 25 '13 at 09:26
I've added additional details to body of answer – Vecnas Jan 27 '13 at 17:44
found out what was wrong, I was using Jackson 2.1.2 but my Spring version was still 3.1 hence did not support this version. Upgraded to 3.2.1 and all is well now. Thanks! – TheZuck Jan 27 '13 at 20:46
@Vecnas Can i override the default `@JsonFormat` of the enum when it is used in another entity ? for example an entity in which i want that the enum should be serialized as a string instead of an object. i try to add another `@JsonFormat` in the field in the class which use the enum but it always serialized as an object. – herau Oct 06 '14 at 13:48
What i have found, use - @JsonSerialize(using = ToStringSerializer.class) for a field, it uses toString(). Not strict solution, but works – Vecnas Oct 07 '14 at 06:25
@Vecnas, you rock!! I was struggling with this for a day :) . Had the exact same problem. its solved with @JsonFormat and + @JsonSerialize – Mayurb Jan 03 '17 at 06:38

score 26 · Answer 3 · edited Apr 20 '17 at 12:53

I've found a very nice and concise solution, especially useful when you cannot modify enum classes as it was in my case. Then you should provide a custom ObjectMapper with a certain feature enabled. Those features are available since Jackson 1.6.

public class CustomObjectMapper extends ObjectMapper {
    @PostConstruct
    public void customConfiguration() {
        // Uses Enum.toString() for serialization of an Enum
        this.enable(WRITE_ENUMS_USING_TO_STRING);
        // Uses Enum.toString() for deserialization of an Enum
        this.enable(READ_ENUMS_USING_TO_STRING);
    }
}

There are more enum-related features available, see here:

https://github.com/FasterXML/jackson-databind/wiki/Serialization-features https://github.com/FasterXML/jackson-databind/wiki/Deserialization-Features

I agree. Furthermore, in Jackson 2.5, you don't need a custom object mapper. Just do this: `objMapper.enable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING);` and this: `objMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING);` — Jake Toronto, Feb 19 '15 at 02:40

gavenkoa · Answer 4 · 2014-06-02T16:16:24.490

Here is my solution. I want transform enum to {id: ..., name: ...} form.

With Jackson 1.x:

pom.xml:

<properties>
    <jackson.version>1.9.13</jackson.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-core-asl</artifactId>
        <version>${jackson.version}</version>
    </dependency>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-mapper-asl</artifactId>
        <version>${jackson.version}</version>
    </dependency>
</dependencies>

Rule.java:

import org.codehaus.jackson.map.annotate.JsonSerialize;
import my.NamedEnumJsonSerializer;
import my.NamedEnum;

@Entity
@Table(name = "RULE")
public class Rule {
    @Column(name = "STATUS", nullable = false, updatable = true)
    @Enumerated(EnumType.STRING)
    @JsonSerialize(using = NamedEnumJsonSerializer.class)
    private Status status;
    public Status getStatus() { return status; }
    public void setStatus(Status status) { this.status = status; }

    public static enum Status implements NamedEnum {
        OPEN("open rule"),
        CLOSED("closed rule"),
        WORKING("rule in work");

        private String name;
        Status(String name) { this.name = name; }
        public String getName() { return this.name; }
    };
}

NamedEnum.java:

package my;

public interface NamedEnum {
    String name();
    String getName();
}

NamedEnumJsonSerializer.java:

package my;

import my.NamedEnum;
import java.io.IOException;
import java.util.*;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;

public class NamedEnumJsonSerializer extends JsonSerializer<NamedEnum> {
    @Override
    public void serialize(NamedEnum value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        Map<String, String> map = new HashMap<>();
        map.put("id", value.name());
        map.put("name", value.getName());
        jgen.writeObject(map);
    }
}

With Jackson 2.x:

pom.xml:

<properties>
    <jackson.version>2.3.3</jackson.version>
</properties>

<dependencies>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>${jackson.version}</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>${jackson.version}</version>
    </dependency>
</dependencies>

Rule.java:

import com.fasterxml.jackson.annotation.JsonFormat;

@Entity
@Table(name = "RULE")
public class Rule {
    @Column(name = "STATUS", nullable = false, updatable = true)
    @Enumerated(EnumType.STRING)
    private Status status;
    public Status getStatus() { return status; }
    public void setStatus(Status status) { this.status = status; }

    @JsonFormat(shape = JsonFormat.Shape.OBJECT)
    public static enum Status {
        OPEN("open rule"),
        CLOSED("closed rule"),
        WORKING("rule in work");

        private String name;
        Status(String name) { this.name = name; }
        public String getName() { return this.name; }
        public String getId() { return this.name(); }
    };
}

Rule.Status.CLOSED translated to {id: "CLOSED", name: "closed rule"}.

score 5 · Answer 5 · answered Mar 04 '17 at 03:55

An easy way to serialize Enum is using @JsonFormat annotation. @JsonFormat can configure the serialization of a Enum in three ways.

@JsonFormat.Shape.STRING
public Enum OrderType {...}

uses OrderType::name as the serialization method. Serialization of OrderType.TypeA is “TYPEA”

@JsonFormat.Shape.NUMBER
Public Enum OrderTYpe{...}

uses OrderType::ordinal as the serialization method. Serialization of OrderType.TypeA is 1

@JsonFormat.Shape.OBJECT
Public Enum OrderType{...}

treats OrderType as a POJO. Serialization of OrderType.TypeA is {"id":1,"name":"Type A"}

JsonFormat.Shape.OBJECT is what you need in your case.

A little more complicated way is your solution, specifying a serializer for the Enum.

Check out this reference: https://fasterxml.github.io/jackson-annotations/javadoc/2.2.0/com/fasterxml/jackson/annotation/JsonFormat.html

score 3 · Answer 6 · answered Oct 04 '16 at 16:05

Use @JsonCreator annotation, create method getType(), is serialize with toString or object working

{"ATIVO"}

or

{"type": "ATIVO", "descricao": "Ativo"}

...

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.JsonNodeType;

@JsonFormat(shape = JsonFormat.Shape.OBJECT)
public enum SituacaoUsuario {

    ATIVO("Ativo"),
    PENDENTE_VALIDACAO("Pendente de Validação"),
    INATIVO("Inativo"),
    BLOQUEADO("Bloqueado"),
    /**
     * Usuarios cadastrados pelos clientes que não possuem acesso a aplicacao,
     * caso venham a se cadastrar este status deve ser alterado
     */
    NAO_REGISTRADO("Não Registrado");

    private SituacaoUsuario(String descricao) {
        this.descricao = descricao;
    }

    private String descricao;

    public String getDescricao() {
        return descricao;
    }

    // TODO - Adicionar metodos dinamicamente
    public String getType() {
        return this.toString();
    }

    public String getPropertieKey() {
        StringBuilder sb = new StringBuilder("enum.");
        sb.append(this.getClass().getName()).append(".");
        sb.append(toString());
        return sb.toString().toLowerCase();
    }

    @JsonCreator
    public static SituacaoUsuario fromObject(JsonNode node) {
        String type = null;
        if (node.getNodeType().equals(JsonNodeType.STRING)) {
            type = node.asText();
        } else {
            if (!node.has("type")) {
                throw new IllegalArgumentException();
            }
            type = node.get("type").asText();
        }
        return valueOf(type);
    }

}

score 1 · Answer 7 · answered Jun 01 '20 at 13:02

In Spring Boot 2, the easiest way is to declare in your application.properties:

spring.jackson.serialization.WRITE_ENUMS_USING_TO_STRING=true
spring.jackson.deserialization.READ_ENUMS_USING_TO_STRING=true

and define the toString() method of your enums.

Serializing enums with Jackson

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