tom91136 tom91136 - 7 months ago 481
Java Question

Jackson databind enum case insensitive

How can I deserialize JSON string that contains enum values that are case insensitive? (using Jackson Databind)

The JSON string:

[{"url": "foo", "type": "json"}]


and my Java POJO:

public static class Endpoint {

public enum DataType {
JSON, HTML
}

public String url;
public DataType type;

public Endpoint() {

}

}


in this case,deserializing the JSON with
"type":"json"
would fail where as
"type":"JSON"
would work.
But I want
"json"
to work as well for naming convention reasons.

Serializing the POJO also results in upper case
"type":"JSON"


I thought of using
@JsonCreator
and @JsonGetter:

@JsonCreator
private Endpoint(@JsonProperty("name") String url, @JsonProperty("type") String type) {
this.url = url;
this.type = DataType.valueOf(type.toUpperCase());
}

//....
@JsonGetter
private String getType() {
return type.name().toLowerCase();
}


And it worked. But I was wondering whether there's a better solutuon because this looks like a hack to me.

I can also write a custom deserializer but I got many different POJOs that use enums and it would be hard to maintain.

Can anyone suggest a better way to serialize and deserialize enums with proper naming convention?

I don't want my enums in java to be lowercase!

Here is some test code that I used:

String data = "[{\"url\":\"foo\", \"type\":\"json\"}]";
Endpoint[] arr = new ObjectMapper().readValue(data, Endpoint[].class);
System.out.println("POJO[]->" + Arrays.toString(arr));
System.out.println("JSON ->" + new ObjectMapper().writeValueAsString(arr));

Answer

In version 2.4.0 you can register a custom serializer for all the Enum types (link to the github issue). Also you can replace the standard Enum deserializer on your own that will be aware about the Enum type. Here is an example:

public class JacksonEnum {

    public static enum DataType {
        JSON, HTML
    }

    public static void main(String[] args) throws IOException {
        List<DataType> types = Arrays.asList(JSON, HTML);
        ObjectMapper mapper = new ObjectMapper();
        SimpleModule module = new SimpleModule();
        module.setDeserializerModifier(new BeanDeserializerModifier() {
            @Override
            public JsonDeserializer<Enum> modifyEnumDeserializer(DeserializationConfig config,
                                                              final JavaType type,
                                                              BeanDescription beanDesc,
                                                              final JsonDeserializer<?> deserializer) {
                return new JsonDeserializer<Enum>() {
                    @Override
                    public Enum deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
                        Class<? extends Enum> rawClass = (Class<Enum<?>>) type.getRawClass();
                        return Enum.valueOf(rawClass, jp.getValueAsString().toUpperCase());
                    }
                };
            }
        });
        module.addSerializer(Enum.class, new StdSerializer<Enum>(Enum.class) {
            @Override
            public void serialize(Enum value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
                jgen.writeString(value.name().toLowerCase());
            }
        });
        mapper.registerModule(module);
        String json = mapper.writeValueAsString(types);
        System.out.println(json);
        List<DataType> types2 = mapper.readValue(json, new TypeReference<List<DataType>>() {});
        System.out.println(types2);
    }
}

Output:

["json","html"]
[JSON, HTML]
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