Format a float as fixed point with Jackson

Question

I've searched the Jackson docs, but can't find any good documentation for the pattern of @JsonFormat for floating point numbers.

Given a field

@JsonProperty("Cost")
private Double cost;

How can I get Jackson to format it as fixed point number with four digits precision in decimal format with @JsonFormat?

PS: I know one should not use floats for money. Spare us the discussion, please.

Answer 1

Building on @Veselin's answers I'm using

public class DoubleDecimalSerializerWithSixDigitPrecisionAndDotSeparator
    extends JsonSerializer<Double> {

  @Override
  public void serialize(Double value, JsonGenerator generator, SerializerProvider serializers)
      throws IOException {
    generator.writeNumber(String.format(Locale.US, "%.6f", value));
  }
}

The use case is the generation of CSVs in Germany, so I don't care for JSON formatting and want a "." as a decimal separator.