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));

Answers


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]

Jackson 2.9

This is now very simple, using jackson-databind 2.9.0 and above

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS);

// objectMapper now deserializes enums in a case-insensitive manner

Full example with tests

import com.fasterxml.jackson.databind.MapperFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {

  private enum TestEnum { ONE }
  private static class TestObject { public TestEnum testEnum; }

  public static void main (String[] args) {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS);

    try {
      TestObject uppercase = 
        objectMapper.readValue("{ \"testEnum\": \"ONE\" }", TestObject.class);
      TestObject lowercase = 
        objectMapper.readValue("{ \"testEnum\": \"one\" }", TestObject.class);
      TestObject mixedcase = 
        objectMapper.readValue("{ \"testEnum\": \"oNe\" }", TestObject.class);

      if (uppercase.testEnum != TestEnum.ONE) throw new Exception("cannot deserialize uppercase value");
      if (lowercase.testEnum != TestEnum.ONE) throw new Exception("cannot deserialize lowercase value");
      if (mixedcase.testEnum != TestEnum.ONE) throw new Exception("cannot deserialize mixedcase value");

      System.out.println("Success: all deserializations worked");
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

I ran into this same issue in my project, we decided to build our enums with a string key and use @JsonValue and a static constructor for serialization and deserialization respectively.

public enum DataType {
    JSON("json"), 
    HTML("html");

    private String key;

    DataType(String key) {
        this.key = key;
    }

    @JsonCreator
    public static DataType fromString(String key) {
        return key == null
                ? null
                : DataType.valueOf(key.toUpperCase());
    }

    @JsonValue
    public String getKey() {
        return key;
    }
}

Since Jackson 2.6, you can simply do this:

    public enum DataType {
        @JsonProperty("json")
        JSON,
        @JsonProperty("html")
        HTML
    }

For a full example, see this gist.


I went for the solution of Sam B. but a simpler variant.

public enum Type {
    PIZZA, APPLE, PEAR, SOUP;

    @JsonCreator
    public static Type fromString(String key) {
        for(Type type : Type.values()) {
            if(type.name().equalsIgnoreCase(key)) {
                return type;
            }
        }
        return null;
    }
}

If you're using Spring Boot 2.1.x with Jackson 2.9 you can simply use this application property:

spring.jackson.mapper.accept-case-insensitive-enums=true


I used a modification of Iago Fernández and Paul solution .

I had an enum in my requestobject which needed to be case insensitive

@POST
public Response doSomePostAction(RequestObject object){
 //resource implementation
}



class RequestObject{
 //other params 
 MyEnumType myType;

 @JsonSetter
 public void setMyType(String type){
   MyEnumType.valueOf(type.toUpperCase());
 }
 @JsonGetter
 public String getType(){
   return myType.toString();//this can change 
 }
}

For those who tries to deserialize Enum ignoring case in GET parameters, enabling ACCEPT_CASE_INSENSITIVE_ENUMS will not do any good. It won't help because this option only works for body deserialization. Instead try this:

public class StringToEnumConverter implements Converter<String, Modes> {
    @Override
    public Modes convert(String from) {
        return Modes.valueOf(from.toUpperCase());
    }
}

and then

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addConverter(new StringToEnumConverter());
    }
}

The answer and code samples are from here


Problem is releated to com.fasterxml.jackson.databind.util.EnumResolver. it uses HashMap to hold enum values and HashMap doesn't support case insensitive keys.

in answers above, all chars should be uppercase or lowercase. but I fixed all (in)sensitive problems for enums with that:

https://gist.github.com/bhdrk/02307ba8066d26fa1537

CustomDeserializers.java

import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.deser.std.EnumDeserializer;
import com.fasterxml.jackson.databind.module.SimpleDeserializers;
import com.fasterxml.jackson.databind.util.EnumResolver;

import java.util.HashMap;
import java.util.Map;


public class CustomDeserializers extends SimpleDeserializers {

    @Override
    @SuppressWarnings("unchecked")
    public JsonDeserializer<?> findEnumDeserializer(Class<?> type, DeserializationConfig config, BeanDescription beanDesc) throws JsonMappingException {
        return createDeserializer((Class<Enum>) type);
    }

    private <T extends Enum<T>> JsonDeserializer<?> createDeserializer(Class<T> enumCls) {
        T[] enumValues = enumCls.getEnumConstants();
        HashMap<String, T> map = createEnumValuesMap(enumValues);
        return new EnumDeserializer(new EnumCaseInsensitiveResolver<T>(enumCls, enumValues, map));
    }

    private <T extends Enum<T>> HashMap<String, T> createEnumValuesMap(T[] enumValues) {
        HashMap<String, T> map = new HashMap<String, T>();
        // from last to first, so that in case of duplicate values, first wins
        for (int i = enumValues.length; --i >= 0; ) {
            T e = enumValues[i];
            map.put(e.toString(), e);
        }
        return map;
    }

    public static class EnumCaseInsensitiveResolver<T extends Enum<T>> extends EnumResolver<T> {
        protected EnumCaseInsensitiveResolver(Class<T> enumClass, T[] enums, HashMap<String, T> map) {
            super(enumClass, enums, map);
        }

        @Override
        public T findEnum(String key) {
            for (Map.Entry<String, T> entry : _enumsById.entrySet()) {
                if (entry.getKey().equalsIgnoreCase(key)) { // magic line <--
                    return entry.getValue();
                }
            }
            return null;
        }
    }
}

Usage:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.module.SimpleModule;


public class JSON {

    public static void main(String[] args) {
        SimpleModule enumModule = new SimpleModule();
        enumModule.setDeserializers(new CustomDeserializers());

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(enumModule);
    }

}

Here's how I sometimes handle enums when I want to deserialize in a case-insensitive manner (building on the code posted in the question):

@JsonIgnore
public void setDataType(DataType dataType)
{
  type = dataType;
}

@JsonProperty
public void setDataType(String dataType)
{
  // Clean up/validate String however you want. I like
  // org.apache.commons.lang3.StringUtils.trimToEmpty
  String d = StringUtils.trimToEmpty(dataType).toUpperCase();
  setDataType(DataType.valueOf(d));
}

If the enum is non-trivial and thus in its own class I usually add a static parse method to handle lowercase Strings.


Deserialize enum with jackson is simple. When you want deserialize enum based in String need a constructor, a getter and a setter to your enum.Also class that use that enum must have a setter which receive DataType as param, not String:

public class Endpoint {

     public enum DataType {
        JSON("json"), HTML("html");

        private String type;

        @JsonValue
        public String getDataType(){
           return type;
        }

        @JsonSetter
        public void setDataType(String t){
           type = t.toLowerCase();
        }
     }

     public String url;
     public DataType type;

     public Endpoint() {

     }

     public void setType(DataType dataType){
        type = dataType;
     }

}

When you have your json, you can deserialize to Endpoint class using ObjectMapper of Jackson:

ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
try {
    Endpoint endpoint = mapper.readValue("{\"url\":\"foo\",\"type\":\"json\"}", Endpoint.class);
} catch (IOException e1) {
        // TODO Auto-generated catch block
    e1.printStackTrace();
}

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