Jackson Custom Serializer for Class extending HashMap

README.md

MyClass must be configured to use Shape.OBJECT in order for Jackson to:

• Use ObjectSerializer instead of MapSerializer
• Invoke MyClassBeanSerializerModifier.modifySerializer

objectMapper
    .configOverride(MyClass.class)
    .setFormat(JsonFormat.Value.forShape(Shape.OBJECT));

Register the serializer modifier:

SimpleModule m = new SimpleModule();
m.setSerializerModifier(new MyClassBeanSerializerModifier());

objectMapper.registerModule(m);

MyClass.java

public class MyClass extends HashMap<String, Object> {
  private String name;
  
  // getter .. setter
}

MyClassBeanSerializerModifier.java

public class MyClassBeanSerializerModifier extends BeanSerializerModifier {

  @Override
  public JsonSerializer<?> modifySerializer(
      final SerializationConfig config,
      final BeanDescription beanDesc,
      final JsonSerializer<?> serializer) {
    if (beanDesc.getBeanClass().equals(MyClass.class)) {
      return new MyClassSerializer(MyClass.class, (JsonSerializer<Object>) serializer);
    }
    return super.modifySerializer(config, beanDesc, serializer);
  }
}

MyClassSerializer.java

public class MyClassSerializer extends StdSerializer<MyClass> {

  private final JsonSerializer<Object> defaultSerializer;
  
  public MyClassSerializer(Class<MyClass> t, JsonSerializer<Object> serializer) {
    super(t);
    this.defaultSerializer = serializer;
  }
  
  @Override
  public void serialize(
      final LedgerAccount value, final JsonGenerator gen, final SerializerProvider provider)
      throws IOException {
    gen.writeStartObject();
    defaultSerializer.unwrappingSerializer(NameTransformer.NOP).serialize(value, gen, provider);
    for (Entry<String, Object> entry : value.entrySet()) {
      String key = entry.getKey();
      Object v = entry.getValue();
      gen.writeObjectField(key, v);
    }
    gen.writeEndObject();
  }
}