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Editorial Team
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Asked: 2026-05-16T09:51:14+00:00

I would like to serialize a HashMap as a string through the Jackson JSON

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I would like to serialize a HashMap as a string through the Jackson JSON processor.
For example:

String strMap = getMapper().writeValueAsString(myHashMap);
result output -> {"r_id":6,"a_am":null,"smb":"Submit","a_li":null,"l_id":878,"pos":[1345,1346,1347]}

I don’t know how to disable null values serialization for Map. It works fine only for POJO if configure the Jackson like this:

mapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL);
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1 Answer

  1. Editorial Team

    For what it’s worth, Jackson 1.6 will have this:

    objectMapper.configure(SerializationConfig.WRITE_NULL_MAP_VALUES, false);

    which does do what you want. Existing method only works for beans, and is not being changed to ensure maximum backwards compatibility.

    EDIT: as per note on comments, this is for Jackson 1.x; Jackson 2.x has matching SerializationFeature

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