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java json jackson

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Accepted Answer
July 4, 2025 Score: 4 Rep: 679 Quality: High Completeness: 60%

Using AbstractTypeResolver

You can use AbstractTypeResolver to add rules on what desired class to instantiate on deserialization.

Let's set a rule to always deserialize Number as BigDecimal. You can create the ObjectMapper like this:

var builder = JsonMapper.builder();
var resolver = new SimpleAbstractTypeResolver();
resolver.addMapping(Number.class, BigDecimal.class);
resolver.addMapping(...);
resolver.addMapping(...);
var module = new SimpleModule();
module.setAbstractTypes(resolver);
builder.addModule(module);
return builder.build();

Using Module only

If you don't have a need to add an additional layer of abstraction, simply add type mapping on the Module itself the following way:

var builder = JsonMapper.builder();
var module = new SimpleModule();
module.addAbstractTypeMapping(Number.class, BigDecimal.class);
builder.addModule(module);
return builder.build();

Test

@Test
void shouldDeserializeAsBigInteger() throws JsonProcessingException {
  Integer a = 2;
  var serialized = objectMapper.writeValueAsString(a);
  var deserialized = objectMapper.readValue(serialized, Number.class);
  assertThat(deserialized).isInstanceOf(BigDecimal.class);
}