Jackson + Builder Pattern?

Question

I'd like Jackson to deserialize a class with the following constructor:

public Clinic(String name, Address address)

Deserializing the first argument is easy. The problem is that Address is defined as:

public class Address {
  private Address(Map<LocationType, String> components)
  ...

  public static class Builder {
    public Builder setCity(String value);
    public Builder setCountry(String value);
    public Address create();
  }
}

and is constructed like this: new Address.Builder().setCity("foo").setCountry("bar").create();

Is there a way to get key-value pairs from Jackson in order to construct the Address myself? Alternatively, is there a way to get Jackson to use the Builder class itself?

Answer 1

As long as you are using Jackson 2+, then there is now built in support for this.

First you need to add this annotation to your Address class:

@JsonDeserialize(builder = Address.Builder.class)

Then you need to add this annotation to your Builder class:

@JsonPOJOBuilder(buildMethodName = "create", withPrefix = "set")

You can skip this second annotation if you are happy to rename your Builder's create method to build, and your Builder's setters to be prefixed to with, instead of set.

Full example:

@JsonDeserialize(builder = Address.Builder.class)
public class Address
{
  private Address(Map<LocationType, String> components)
  ...

  @JsonPOJOBuilder(buildMethodName = "create", withPrefix = "set")
  public static class Builder
  {
    public Builder setCity(String value);
    public Builder setCountry(String value);
    public Address create();
  }
}

Answer 2

The answer from @Rupert Madden-Abbott works. However, if you have a non-default constructor, e.g.,

Builder(String city, String country) {...}

Then you should annotate the parameters as below:

@JsonCreator
Builder(@JsonProperty("city")    String city, 
        @JsonProperty("country") String country) {...}

Answer 3

A solution which was suitable for me in this case (I used "Lombok" builder annotation).

@Getter
@Builder(builderMethodName = "builder")
@NoArgsConstructor(access = AccessLevel.PRIVATE)
@AllArgsConstructor(access = AccessLevel.PRIVATE)
@JsonAutoDetect(
    fieldVisibility = JsonAutoDetect.Visibility.ANY,
    creatorVisibility = JsonAutoDetect.Visibility.ANY
)

I hope would be useful for u too.

Answer 4

I ended up implementing this using the @JsonDeserialize as follows:

@JsonDeserialize(using = JacksonDeserializer.class)
public class Address
{...}

@JsonCachable
static class JacksonDeserializer extends JsonDeserializer<Address>
{
    @Override
    public Address deserialize(JsonParser parser, DeserializationContext context)
        throws IOException, JsonProcessingException
    {
        JsonToken token = parser.getCurrentToken();
        if (token != JsonToken.START_OBJECT)
        {
            throw new JsonMappingException("Expected START_OBJECT: " + token, parser.getCurrentLocation());
        }
        token = parser.nextToken();
        Builder result = new Builder();
        while (token != JsonToken.END_OBJECT)
        {
            if (token != JsonToken.FIELD_NAME)
            {
                throw new JsonMappingException("Expected FIELD_NAME: " + token, parser.getCurrentLocation());
            }
            LocationType key = LocationType.valueOf(parser.getText());

            token = parser.nextToken();
            if (token != JsonToken.VALUE_STRING)
            {
                throw new JsonMappingException("Expected VALUE_STRING: " + token, parser.getCurrentLocation());
            }
            String value = parser.getText();

            // Our Builder allows passing key-value pairs
            // alongside the normal setter methods.
            result.put(key, value);
            token = parser.nextToken();
        }
        return result.create();
    }
}

Answer 5

This worked for me: @NoArgsConstructor The only drawback of this, is that one can do = new ADTO() again. But, hey, I dont like de code police anyhow, telling me how to use someones code :-) So, use my POJO DTOS the way you like it. With or without builder. I suggest: do it with a Builder, but be my guest...

@Data
@Builder
//Dont forget this! Otherwise no Jackson serialisation possible!
@NoArgsConstructor
@AllArgsConstructor
public class ADTO {
.....
}

Answer 6

There is no support currently for builder pattern, although it has been requested quite a while ago (and finally Jira issue http://jira.codehaus.org/browse/JACKSON-469 was filed) -- it is something that may be added for 1.8 release if there is enough demand (make sure to vote at Jira!). It is a reasonable additional feature, and only delayed by amount of time developers have. But I think it would be great addition.