Change JSON value from null to empty String

Question

im making a rest controller which return json. i get this data from database, mapping in to java class using setter getter.

{
  "example": null,
  "this": null,
  "is": null,
  "only": null,
  "example": null,
  "foo": null,
  "bar": null,
  "blabla": null,
  "lala": null
}

its because the data in database not present. but i want the data to be like this:

{
      "example": ""    ,
      "this": "",
      "is": "",
      "only": "",
      "example": "",
      "foo": "",
      "bar": "",
      "blabla": "",
      "lala": ""
 }

i have more than 100 fields. so i think its not good to use if else in every variable.

How are you deserializing the json? Can you add that logic there? — Tomer Shetah
– Tomer Shetah, Commented Sep 22, 2020 at 8:26
@TomerShetah im using ObjectMapper.valueToTree, it still get null. im using class and then return to controller still get null too. — Vodka
– Vodka, Commented Sep 22, 2020 at 12:58

jumb0jet · Accepted Answer · 2020-09-21 22:20:31Z

2

You can override default ObjectMapper (provided by Spring Boot auto-configuration) and configure globally format to use for properties of type String.

@Configuration
public class JacksonConfiguration {

    @Bean
    ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
        final var objectMapper = builder.createXmlMapper(false).build();
        objectMapper.configOverride(String.class).setSetterInfo(JsonSetter.Value.forValueNulls(Nulls.AS_EMPTY));
        return objectMapper;
    }

}

answered Sep 21, 2020 at 22:20

jumb0jet

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5 Comments

Vodka Over a year ago

is var in java8 equals object?

jumb0jet Over a year ago

var can be used in a local variable declaration instead of the variable's type. It's available since Java 10. Java 8 equivalent syntax is - final ObjectMapper objectMapper = ...

Vodka Over a year ago

it still get null if the data in db not present.

jumb0jet Over a year ago

make sure you injected ObjectMapper configured by Spring into your controller.

Vodka Over a year ago

@Autowired private ObjectMapper mapper; and then JsonNode tes = mapper.valueToTree(result); still get null

user3030484 · Accepted Answer · 2022-03-15 19:16:00Z

0

DefaultSerializerProvider.Impl sp = new DefaultSerializerProvider.Impl();
sp.setNullValueSerializer(new NullSerializer());
new ObjectMapper().setSerializerProvider(sp)...

Where

public class NullSerializer extends JsonSerializer<Object> {
    @Override
    public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeString("");
    }
}

answered Mar 15, 2022 at 19:16

user3030484

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Comments

4b0 · Accepted Answer · 2022-06-02 09:22:29Z

0

You can solve it more easily by handling json string:

jsonString = jsonString.replaceAll("null,", "'',");

edited Jun 2, 2022 at 9:22

4b0

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answered Jun 2, 2022 at 9:02

Thông

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