Java to Jackson JSON serialization: Money fields

Currently, I'm using Jackson to send out JSON results from my Spring-based web application.

The problem I'm having is trying to get all money fields to output with 2 decimal places. I wasn't able to solve this problem using setScale(2), as numbers like 25.50 are truncated to 25.5 etc

Has anyone else dealt with this problem? I was thinking about making a Money class with a custom Jackson serializer... can you make a custom serializer for a field variable? You probably can... But even still, how could I get my customer serializer to add the number as a number with 2 decimal places?

You can use a custom serializer at your money field. Here's an example with a MoneyBean. The field amount gets annotated with @JsonSerialize(using=...).

public class MoneyBean {
    //...

    @JsonProperty("amountOfMoney")
    @JsonSerialize(using = MoneySerializer.class)
    private BigDecimal amount;

    //getters/setters...
}

public class MoneySerializer extends JsonSerializer<BigDecimal> {
    @Override
    public void serialize(BigDecimal value, JsonGenerator jgen, SerializerProvider provider) throws IOException,
            JsonProcessingException {
        // put your desired money style here
        jgen.writeString(value.setScale(2, BigDecimal.ROUND_HALF_UP).toString());
    }
}

That's it. A BigDecimal is now printed in the right way. I used a simple testcase to show it:

@Test
public void jsonSerializationTest() throws Exception {
     MoneyBean m = new MoneyBean();
     m.setAmount(new BigDecimal("20.3"));

     ObjectMapper mapper = new ObjectMapper();
     assertEquals("{\"amountOfMoney\":\"20.30\"}", mapper.writeValueAsString(m));
}

You can use @JsonFormat annotation with shape as STRING on your BigDecimal variables. Refer below:

 import com.fasterxml.jackson.annotation.JsonFormat;

  class YourObjectClass {

      @JsonFormat(shape=JsonFormat.Shape.STRING)
      private BigDecimal yourVariable;

 }

Instead of setting the @JsonSerialize on each member or getter you can configure a module that use a custome serializer for a certain type:

SimpleModule module = new SimpleModule();
module.addSerializer(BigInteger.class, new ToStringSerializer());
objectMapper.registerModule(module);

In the above example, I used the to string serializer to serialize BigIntegers (since javascript can not handle such numeric values).

I'm one of the maintainers of jackson-datatype-money, so take this answer with a grain of salt since I'm certainly biased. The module should cover your needs and it's pretty light-weight (no additional runtime dependencies). In addition it's mentioned in the Jackson docs, Spring docs and there were even some discussions already about how to integrate it into the official ecosystem of Jackson.

I had the same issue and i had it formatted into JSON as a String instead. Might be a bit of a hack but it's easy to implement.

private BigDecimal myValue = new BigDecimal("25.50");
...
public String getMyValue() {
    return myValue.setScale(2, BigDecimal.ROUND_HALF_UP).toString();
}

As Sahil Chhabra suggested you can use @JsonFormat with proper shape on your variable. In case you would like to apply it on every BigDecimal field you have in your Dto's you can override default format for given class.

@Configuration
public class JacksonObjectMapperConfiguration {

    @Autowired
    public void customize(ObjectMapper objectMapper) {
         objectMapper
            .configOverride(BigDecimal.class).setFormat(JsonFormat.Value.forShape(JsonFormat.Shape.STRING));
    }
}

Inspired by Steve, and as the updates for Java 11. Here's how we did the BigDecimal reformatting to avoid scientific notation.

public class PriceSerializer extends JsonSerializer<BigDecimal> {
    @Override
    public void serialize(BigDecimal value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
        // Using writNumber and removing toString make sure the output is number but not String.
        jgen.writeNumber(value.setScale(2, RoundingMode.HALF_UP));
    }
}