How to serialize list of enums from rest api

Question

I want to return a list of enums from a rest api call, and have it show the value of the enum rather than just the enum names, in JSON format. Currently my rest call returns json looking like:

{
  "responses": [
    "ACTION_TAKEN",
    "IGNORED",
    "UNDETECTED"
  ]
}

But, I want it to be more like (or something like this):

{
  "responses": [
    {
      "name":"ACTION_TAKEN",
      "value":"Action Taken"
    },
    {
      "name":"IGNORED",
      "value":"Ignored"
    },
    {
      "name":"UNDETECTED",
      "value":"Undetected"
    }
   ]
}

My enum looks like:

public enum Response {

  ACTION_TAKEN ("Action Taken"),
  IGNORED ("Ignored"),
  UNDETECTED("Undetected");

  private String value;

  Response(String value) {
    this.value = value;
  }

  public String getValue() {
    return this.value;
  }

  @Override
  public String toString() {
    return value;
  }
}

My model object looks like this. For the sake of this example, it just has a list of enum values.

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class StaticData {

  private List<Response> responses;

  public List<Response> getResponses() {
    return responses;
  }

  public void setResponses(List<Response> responses) {
    this.responses = responses;
  }
}

The web service method looks like:

@Component
@Path("staticData")
@Produces("application/json")
@Consumes("application/json")
public class StaticDataResource {

  @GET
  public Response getCurrentContent() {
    StaticData staticData = new StaticData();
    staticData.setResponses(Arrays.asList(Response.values()));
    return Response.ok(staticData).build();
  }
}

Here are the dependencies from my effective pom (sorry for the bad formatting)

<dependencies>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
    <version>4.2.5.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>com.sun.jersey.contribs</groupId>
    <artifactId>jersey-spring</artifactId>
    <version>1.19.1</version>
    <scope>compile</scope>
    <exclusions>
      <exclusion>
        <artifactId>*</artifactId>
        <groupId>org.springframework</groupId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>com.thetransactioncompany</groupId>
    <artifactId>cors-filter</artifactId>
    <version>2.4</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>4.2.5.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>4.2.5.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-expression</artifactId>
    <version>4.2.5.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-oxm</artifactId>
    <version>4.2.5.RELEASE</version>
    <scope>compile</scope>
  </dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-orm</artifactId>
  <version>4.2.5.RELEASE</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4j-api</artifactId>
  <version>1.7.19</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4j-log4j12</artifactId>
  <version>1.7.19</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>commons-logging</groupId>
  <artifactId>commons-logging</artifactId>
  <version>1.2</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>commons-io</groupId>
  <artifactId>commons-io</artifactId>
  <version>2.4</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>19.0</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.reflections</groupId>
  <artifactId>reflections</artifactId>
  <version>0.9.10</version>
  <scope>compile</scope>
  <exclusions>
    <exclusion>
      <artifactId>guava</artifactId>
      <groupId>com.google.guava</groupId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>3.0.1</version>
  <scope>provided</scope>
</dependency>
<dependency>
  <groupId>javax.ws.rs</groupId>
  <artifactId>javax.ws.rs-api</artifactId>
  <version>2.0.1</version>
  <scope>provided</scope>
</dependency>
<dependency>
  <groupId>org.eclipse.persistence</groupId>
  <artifactId>javax.persistence</artifactId>
  <version>2.1.0</version>
  <scope>provided</scope>
</dependency>
<dependency>
  <groupId>javax.ejb</groupId>
  <artifactId>javax.ejb-api</artifactId>
  <version>3.2</version>
  <scope>provided</scope>
</dependency>
  <dependency>
      <groupId>javax.transaction</groupId>
      <artifactId>jta</artifactId>
      <version>1.1</version>
      <scope>provided</scope>
    </dependency>
</dependencies>

I have tried adding @JsonFormat(shape = JsonFormat.Shape.Object) to the top of my enum class. It didn't work. I tried adding @JsonValue to above my getValue() method in the enum class, and that didn't work either. I tried adding a custom serializer extending StdSerializer or JsonSerializer, and referencing that class above my enum using @JsonSerialize(using = ReasonSerializer). I put a breakpoint in the serialize method and didn't hit it, so that didn't work. I looked a little bit at doing implements ContextResolver<ObjectMapper>, but couldn't quite figure that out, or whether that was even the right path to go down or not.

Any help is greatly appreciated! Thanks!

What are these two methods return Response.ok(staticData).build(); — Mandrek, Aug 05 '20 at 10:01

score 8 · Answer 1 · edited Jun 20 '20 at 09:12

Final solution

This works with JAX-RS and I have tested it with your code.

Use @JsonFormat with public String getName().

@JsonFormat(shape=JsonFormat.Shape.OBJECT)
public enum Response {
    ACTION_TAKEN ("Action Taken"),
    IGNORED ("Ignored"),
    UNDETECTED("Undetected");

    private String value;

    Response(String value) {
        this.value = value;
    }
    // Getters, Setters

    public String getName() {
        return name();
    }
}

JSON output

{
    "responses": [{
            "value": "Action Taken",
            "name": "ACTION_TAKEN"
        }, {
            "value": "Ignored",
            "name": "IGNORED"
        }, {
            "value": "Undetected",
            "name": "UNDETECTED"
        }
    ]
}

Tested using the following dependency.

import com.fasterxml.jackson.annotation.JsonFormat;

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.9.6</version>
</dependency>

Alternative solution

Jackson docs states that behavior may change depending on what serializer is being used. So if the first solution doesn't work, this one might.

@JsonFormat(shape=JsonFormat.Shape.OBJECT)
public enum Response {
    ACTION_TAKEN ("Action Taken"),
    IGNORED ("Ignored"),
    UNDETECTED("Undetected");

    private String name;
    private String value;

    Response(String value) {
        name = name();
        this.value = value;
    }
    
    public String getName() {
        return name;
    }
    
    public String getValue() {
        return value;
    }
}

I agree that this works, but unfortunately, it doesn't solve my problem. I am returning the whole object from the api call using Response.ok(staticData).build(), not using writeValueAsString. — Jess, Dec 13 '18 at 14:02
@Jessica Rewritten my answer again. It should now work with your code. Please let me know of your results. :) — J.A.P, Dec 13 '18 at 18:46
Just tried what you suggested: adding the JsonFormat annotation to the enum class and then adding the getName method. It didn't work. No difference in output for me. — Jess, Dec 13 '18 at 19:27
@Jessica I added the dependency I am using to the answer. See if that makes a difference. Make sure the import is identical. If that doesn't help, what application server are you using and what version? — J.A.P, Dec 13 '18 at 19:39
@Jessica Also added an alternative solution that may work better for you. — J.A.P, Dec 13 '18 at 20:00

score -1 · Answer 2 · answered Dec 12 '18 at 23:58

According to this page: https://www.javaworld.com/article/2072870/java-enums-are-inherently-serializable.html Every Enum is naturally serializable, so yours should work too.

But, you should consider what was said here: Is custom enum Serializable too?

Summary: "Enum constants are serialized differently than ordinary serializable or externalizable objects. The serialized form of an enum constant consists solely of its name; field values of the constant are not present in the form"

To solve your problem I would consider using a simple Pojo class to represent your serializable class. If you still wants to use a Enum, then you could use a translator Pojo <-> Enum (I do not recomend doing this last option because of the redundancy, but last word should be yours depending on what you want to do with it :) ).

How to serialize list of enums from rest api

2 Answers2

Final solution

Alternative solution