How to serialize to java.util.List and java.util.Map with Jackson

Question

Is it possible to serialize Java objects to lists and maps with Jackson library directly? I mean not to String, not to byte[], but to java.util.Map and java.util.List.

This might be helpful when filtering out unnecessary fields dynamically.

I can do it in two steps, by first converting to String.

ObjectMapper mapper = new ObjectMapper()
DTO dto = new DTO();
DTO[] dtos = {dto};
mapper.readValue(mapper.writeValueAsString(dto), Object.class); // Map
mapper.readValue(mapper.writeValueAsString(dtos), Object.class); // List

Michał Ziober · Accepted Answer · 2019-03-19 22:59:00Z

2

Use convertValue method:

ObjectMapper objectMapper = new ObjectMapper();
Map map = objectMapper.convertValue(new Person(), Map.class);
System.out.println(map);

It works as well for Object.class as a target type:

ObjectMapper objectMapper = new ObjectMapper();
Object map = objectMapper.convertValue(new Person(), Object.class);
Object array = objectMapper.convertValue(Collections.singleton(new Person()), Object.class);
System.out.println(map);
System.out.println(array);

prints:

{name=Rick, lastName=Bricky}
[{name=Rick, lastName=Bricky}]

edited Mar 19, 2019 at 22:59

answered Mar 19, 2019 at 22:39

Michał Ziober

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2 Comments

Vytenis Bivainis Over a year ago

mapper.convertValue(object, Object.class) also works.

Michał Ziober Over a year ago

@VytenisBivainis, It is a little bit counterintuitive but if you need this level of abstraction and it works for you why not. I will add it to an answer. I always used Map and List as target classes but today I learned it works as expected for Object.class as well. Thanks, I learned something new too!

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