Jackson 数据绑定枚举不区分大小写

Question

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 1

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();
    }
  }
}

Answer 2

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;
    }
}

Answer 3

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 .

Answer 4

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]

Answer 5

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;
    }
}

Answer 6

如果您将 Spring Boot 2.1.x与 Jackson 2.9使用，您可以简单地使用此应用程序属性：

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

Answer 7

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

Answer 8

To allow case insensitive deserialization of enums in jackson, simply add the below property to the application.properties file of your spring boot project.

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

If you have the yaml version of properties file, add below property to your application.yml file.

spring:
  jackson:
    mapper:
      accept-case-insensitive-enums: true

Answer 9

With apologies to @Konstantin Zyubin, his answer was close to what I needed - but I didn't understand it, so here's how I think it should go:

If you want to deserialize one enum type as case insensitive - ie you don't want to, or can't, modify the behavior of the entire application, you can create a custom deserializer just for one type - by sub-classing StdConverter and force Jackson to use it only on the relevant fields using the JsonDeserialize annotation.

Example:

public class ColorHolder {

  public enum Color {
    RED, GREEN, BLUE
  }

  public static final class ColorParser extends StdConverter<String, Color> {
    @Override
    public Color convert(String value) {
      return Arrays.stream(Color.values())
        .filter(e -> e.getName().equalsIgnoreCase(value.trim()))
        .findFirst()
        .orElseThrow(() -> new IllegalArgumentException("Invalid value '" + value + "'"));
    }
  }

  @JsonDeserialize(converter = ColorParser.class)
  Color color;
}

Answer 10

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);
    }

}

Answer 11

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

Answer 12

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.

Answer 13

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();
}