Case insensitive JSON to POJO mapping without changing the POJO

Question

Does anyone know how com.fasterxml.jackson.databind.ObjectMapper is able to map JSON properties to POJO properties case insensitive?

JSON-String:

[{"FIRSTNAME":"John","LASTNAME":"Doe","DATEOFBIRTH":"1980-07-16T18:25:00.000Z"}]

POJO-Class:

public class Person {

    private String firstName;
    private String lastName;
    private Date dateOfBirth;

    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public Date getDateOfBirth() {
        return dateOfBirth;
    }
    public void setDateOfBirth(Date dateOfBirth) {
        this.dateOfBirth = dateOfBirth;
    }
}

Test-Class:

@Test
public final void testDeserializingPersonJsonToPersonClass()
        throws JsonParseException, JsonMappingException, IOException {
    final String jsonAsString = "[{\"FIRSTNAME\":\"John\",\"LASTNAME\":\"Doe\",\"DATEOFBIRTH\":\"1980-07-16T18:25:00.000Z\"}]";
    final ObjectMapper mapper = new ObjectMapper();

    final Person person = mapper.readValue(jsonAsString, Person.class);

    assertNotNull(person);
    assertThat(person.getFirstName(), equalTo("John"));
}

This ends up in following error:
com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of ...

It's not possible to change neither JSON-String nor POJO-Class.

Answer 1

This behaviour was introduced in Jackson 2.5.0. You can configure the mapper to be case insensitive using MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES.

For example :

ObjectMapper mapper = new ObjectMapper();
mapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);

Answer 2

I had the same problem and couldn't find a global way of solving this. However you can have 2 setters per property to achieve this:

@JsonSetter("FIRSTNAME")
public void setFirstNameCaps(String firstName) {
    this.firstName = firstName;
}

@JsonSetter("firstName")
public void setFirstName(String firstName) {
    this.firstName = firstName;
}

Not elegant but will work for both upper and lower case json fields. You can also try the solution mentioned here but this might have a performance overhead

Answer 3

You can solve this problem by configuring the mapper, as described by the @Nicolas Riousset.

In addition, since version Jackson 2.9 you can do the same using annotation @JsonFormat(with = JsonFormat.Feature.ACCEPT_CASE_INSENSITIVE_PROPERTIES) over a field or class, which is a more flexible option.

@JsonFormat(with = JsonFormat.Feature.ACCEPT_CASE_INSENSITIVE_PROPERTIES)
private String firstName;

Answer 4

I was in the same kind of situation and had to convert to a map and then copy the values over manually.

import com.fasterxml.jackson.core.type.TypeReference;

Map<String, String> map = 
    mapper.readValue(jsonAsString, new TypeReference<Map<String, String>>(){});