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:

Answer 1

An alternative solution is to specify JSON field names case-sensitive:

public Movie(){
    //Jackson deserialize
}
@JsonProperty("Title")
public String getTitle() {
    return title;
}

@JsonProperty("Year")
public String getYear() {
    return year;
}
@JsonProperty("imdbID")
public String getImdbID() {
    return imdbID;
}

Answer 2

package br.com.marcusvoltolim.util;


import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.MapperFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.log4j.Log4j;

@Log4j
public class JsonUtils {

    private static final ObjectMapper OBJECT_MAPPER;

    static {
        OBJECT_MAPPER = new ObjectMapper();
        OBJECT_MAPPER.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);
        OBJECT_MAPPER.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    }

    public static <T> T fromJson(final String json, final Class<T> classe) {
        try {
            return OBJECT_MAPPER.readValue(json, classe);
        } catch (Exception e) {
            log.error(e);
            try {
                return classe.newInstance();
            } catch (InstantiationException | IllegalAccessException ex) {
                return null;
            }
        }
    }

}

Answer 3

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 4

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 5

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 6

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>>(){});