Lombok Serialize and Deserialize @Builder Class

Lombok @Builder generates a builder for our class, and Gson serializes and deserializes such a class without extra configuration, whereas Jackson serializes it directly but needs @Jacksonized or @JsonDeserialize to deserialize it. Serialization converts a Java object to JSON, and deserialization converts the JSON back to a Java object. We need both conversions when a REST API sends or receives a class that Lombok builds.

The following example uses the Article class, which has the fields id, title and tags. We created this class in the Lombok @Builder tutorial.

@Builder
@Getter
@ToString
public class Article {

  private Long id;
  private String title;
  private List<String> tags;
}

1. Serializing @Builder Class

Gson and Jackson both serialize a class annotated with @Builder without extra configuration.

1.1. Gson

The Gson method toJson() serializes the Article object to JSON..

Article article = Article.builder(1L)
  .title("Test Article")
  .tag("Test Tag")
  .build();

//With Gson
Gson gson = new Gson();
String gsonJson = gson.toJson(article);

//Prints {"id":1,"title":"Test Article","tags":["Test Tag"]}
System.out.println(gsonJson); 

1.2. Jackson

The Jackson method writeValueAsString() serializes the Article object to JSON.

Article article = Article.builder(1L)
  .title("Test Article")
  .tag("Test Tag")
  .build();

//With Jackson
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(article);

//Prints {"id":1,"title":"Test Article","tags":["Test Tag"]}
System.out.println(json); 

2. Deserializing @Builder Class

2.1. Gson

Gson reads the JSON back into an Article object with the method fromJson() and needs no extra configuration for deserialization.

String json = "{\"id\":1,\"title\":\"Test Title\",\"tags\":[\"Test Tag\"]}";

Gson gson = new Gson();
Article gsonArticle = gson.fromJson(json, Article.class);

//Prints Article(id=1, title=Test Title, tags=[Test Tag])
System.out.println(gsonArticle);

2.2. Jackson

By default, Jackson throws the runtime exception InvalidDefinitionException when we deserialize the Article class. Jackson cannot construct the object because the class has no default no-args constructor.

ObjectMapper mapper = new ObjectMapper();
String json = "{\"id\":1,\"title\":\"Test Title\",\"tags\":[\"Test Tag\"]}";
Article article = mapper.readValue(json, Article.class);
System.out.println(article);

Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: 
Cannot construct instance of `com.howtodoinjava.demo.lombok.Article` 
(no Creators, like default constructor, exist): cannot deserialize from Object value 
(no delegate- or property-based Creator)
 at [Source: (String)"{"id":1,"title":"Test Title","tags":["Test Tag"]}"; line: 1, column: 2]

2.2.1. Lombok @Jacksonized

The Lombok annotation @Jacksonized is the simplest solution for deserializing with Jackson. We annotate the @Builder class with @Jacksonized, and Jackson converts the JSON string to a Java object.

@Builder(toBuilder = true)
@Getter
@ToString
@Jacksonized
public class Article {
    ...
}

String json = "{\"id\":1,\"title\":\"Test Title\",\"tags\":[\"Test Tag\"]}";

ObjectMapper mapper = new ObjectMapper();
Article article = mapper.readValue(json, Article.class);

//prints Article(id=1, title=Test Title, tags=[Test Tag])
System.out.println(article);

2.2.2. Jackson @JsonDeserialize and @JsonPOJOBuilder

The annotation @Jacksonized is an experimental feature, so Lombok may remove it in a future version. Another way to make @Builder work with Jackson is to add Jackson annotations that tell Jackson how to create an instance of the Article class.

Two Jackson annotations support this.

• @JsonDeserialize specifies a custom deserializer that unmarshals the JSON.
• @JsonPOJOBuilder configures the details of a builder class.

@Builder
@Getter
@ToString
@JsonDeserialize(builder = Article.ArticleBuilder.class)
public class Article {
  private Long id;
  private String title;
  private List<String> tags;

  @JsonPOJOBuilder(withPrefix="")
  public static class ArticleBuilder {
  }
}

String json = "{\"id\":1,\"title\":\"Test Title\",\"tags\":[\"Test Tag\"]}";

ObjectMapper mapper = new ObjectMapper();
Article article = mapper.readValue(json, Article.class);

//Prints Article(id=1, title=Test Title, tags=[Test Tag])
System.out.println(article);

3. Conclusion

Gson serializes and deserializes classes annotated with Lombok @Builder without extra configuration, so it is the simplest choice.

If we must use Jackson, @Jacksonized needs the least code. If Lombok removes @Jacksonized in a future version, we can use the Jackson annotations @JsonDeserialize and @JsonPOJOBuilder instead.

Happy Learning !!

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