import com.fasterxml.jackson.core.JsonGenerationException; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.*; import com.fasterxml.jackson.databind.annotation.JsonSerialize; import com.fasterxml.jackson.databind.ser.ContextualSerializer; import com.fasterxml.jackson.databind.ser.std.StdSerializer; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import java.io.IOException; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; // Create own annotation storing your unit value @Target({ ElementType.FIELD }) @Retention(RetentionPolicy.RUNTIME) @interface Unit { String value(); } // Create custom serializer checking @Unit annotation class UnitSerializer extends StdSerializer<Integer> implements ContextualSerializer { private String unit; public UnitSerializer() { super(Integer.class); } public UnitSerializer(String unit) { super(Integer.class); this.unit = unit; } @Override public void serialize(Integer value, JsonGenerator jgen, SerializerProvider provider) throws IOException { jgen.writeString(String.format("%d %s", value, unit)); } @Override public JsonSerializer<?> createContextual(SerializerProvider prov, BeanProperty property) throws JsonMappingException { String unit = null; Unit ann = null; if (property != null) { ann = property.getAnnotation(Unit.class); } if (ann != null) { unit = ann.value(); } return new UnitSerializer(unit); } } @NoArgsConstructor @AllArgsConstructor @Data class X { @JsonSerialize(using = UnitSerializer.class) @Unit("mm") private int length; } public class Runner { public static void main(String[] args) throws JsonProcessingException { X x = new X(10); ObjectMapper objectMapper = new ObjectMapper(); System.out.println(objectMapper.writeValueAsString(x)); } }

Resultado:

 {"length":"10 mm"}