Jackson enum Serializing and DeSerializer

Question

I m using JAVA 1 6 and Jackson 1 9 9 I ve got an enum  public enum Event       FORGOT PASSWORD  forgot password         private final String value       private Event final String description            this value   description              JsonValue     final String value             return this value            I ve added a  JsonValue  this seems to do the job it serializes the object into     event   forgot password     but when I try to deserialize I get a  Caused by  org codehaus jackson map JsonMappingException  Can not construct instance of com globalrelay gas appsjson authportal Event from String value  forgot password   value not one of declared Enum instance names   What am I missing here

User · Answer

You should create a static factory method which takes single argument and annotate it with @JsonCreator (available since Jackson 1.2)

@JsonCreator
public static Event forValue(String value) { ... }

Read more about JsonCreator annotation here.

User · Answer

I ve found a very nice and concise solution  especially useful when you cannot modify enum classes as it was in my case  Then you should provide a custom ObjectMapper with a certain feature enabled  Those features are available since Jackson 1 6  So you only need to write toString   method in your enum   public class CustomObjectMapper extends ObjectMapper        PostConstruct     public void customConfiguration                Uses Enum toString   for serialization of an Enum         this enable WRITE ENUMS USING TO STRING              Uses Enum toString   for deserialization of an Enum         this enable READ ENUMS USING TO STRING             There are more enum-related features available  see here   https   github com FasterXML jackson-databind wiki Serialization-Features https   github com FasterXML jackson-databind wiki Deserialization-Features

User · Answer

Besides using  JsonSerialize  JsonDeserialize  you can also use SerializationFeature and DeserializationFeature  jackson binding  in the object mapper   Such as DeserializationFeature READ UNKNOWN ENUM VALUES USING DEFAULT VALUE  which give default enum type if the one provided is not defined in the enum class

User · Answer

Here is another example that uses string values instead of a map   public enum Operator       EQUAL new String                         NOT EQUAL new String          lt  gt          LESS THAN new String     lt          LESS THAN EQUAL new String     lt           GREATER THAN new String     gt          GREATER THAN EQUAL new String     gt           EXISTS new String    not null    exists         NOT EXISTS new String    is null    not exists         MATCH new String    match          private String   value       Operator String   value            this value   value              JsonValue     public String toStringOperator            return value 0               JsonCreator     public static Operator fromStringOperator String stringOperator            if stringOperator    null                for Operator operator   Operator values                      for String operatorString   operator value                        if  stringOperator equalsIgnoreCase operatorString                             return operator                                                                          return null

User · Answer

Try this   public enum Event        FORGOT PASSWORD  forgot password         private final String value       private Event final String description            this value   description             private Event             this value   this name                JsonValue     final String value             return this value

User · Answer

Note that as of this commit in June 2015  Jackson 2 6 2 and above  you can now simply write  public enum Event        JsonProperty  quot forgot password quot       FORGOT PASSWORD     The behavior is documented here  https   fasterxml github io jackson-annotations javadoc 2 11 com fasterxml jackson annotation JsonProperty html  Starting with Jackson 2 6 this annotation may also be used to change serialization of Enum like so   public enum MyEnum          JsonProperty  quot theFirstValue quot   THE FIRST VALUE         JsonProperty  quot another value quot   ANOTHER VALUE      as an alternative to using JsonValue annotation

User · Answer

You can customize the deserialization for any attribute   Declare your deserialize class using the annotationJsonDeserialize  import com fasterxml jackson databind annotation JsonDeserialize  for the attribute that will be processed  If this is an Enum    JsonDeserialize using   MyEnumDeserialize class  private MyEnum myEnum    This way your class will be used to deserialize the attribute  This is a full example   public class MyEnumDeserialize extends JsonDeserializer lt MyEnum gt          Override     public MyEnum deserialize JsonParser jsonParser  DeserializationContext deserializationContext  throws IOException           JsonNode node   jsonParser getCodec   readTree jsonParser           MyEnum type   null          try              if node get  attr      null                   type   MyEnum get Long parseLong node get  attr   asText                      if  type    null                        return type                                           catch Exception e               type   null                    return type

User · Answer

There are various approaches that you can take to accomplish deserialization of a JSON object to an enum  My favorite style is to make an inner class   import com fasterxml jackson annotation JsonCreator  import com fasterxml jackson annotation JsonFormat  import com fasterxml jackson annotation JsonProperty  import org hibernate validator constraints NotEmpty   import java util Arrays  import java util Map  import java util function Function  import java util stream Collectors   import static com fasterxml jackson annotation JsonFormat Shape OBJECT    JsonFormat shape   OBJECT  public enum FinancialAccountSubAccountType     MAIN  Main      MAIN DISCOUNT  Main Discount       private final static Map lt String  FinancialAccountSubAccountType gt  ENUM NAME MAP    static       ENUM NAME MAP   Arrays stream FinancialAccountSubAccountType values           collect Collectors toMap          Enum  name          Function identity             private final String displayName     FinancialAccountSubAccountType String displayName        this displayName   displayName          JsonCreator   public static FinancialAccountSubAccountType fromJson Request request        return ENUM NAME MAP get request getCode             JsonProperty  name     public String getDisplayName         return displayName         private static class Request        NotEmpty message    Financial account sub-account type code is required       private final String code      private final String displayName        JsonCreator     private Request  JsonProperty  code   String code                       JsonProperty  name   String displayName          this code   code        this displayName   displayName             public String getCode           return code              JsonProperty  name       public String getDisplayName           return displayName

User · Answer

In my case  this is what resolved   import com fasterxml jackson annotation JsonCreator  import com fasterxml jackson annotation JsonFormat  import com fasterxml jackson annotation JsonProperty    JsonFormat shape   JsonFormat Shape OBJECT  public enum PeriodEnum        DAILY 1       WEEKLY 2              private final int id       PeriodEnum int id            this id   id             public int getId             return id             public String getName             return this name                JsonCreator     public static PeriodEnum fromJson  JsonProperty  name   String name            return valueOf name              Serializes and deserializes the following json        id   2     name    WEEKLY      I hope it helps

User · Answer

Actual Answer   The default deserializer for enums uses  name   to deserialize  so it s not using the  JsonValue   So as  OldCurmudgeon pointed out  you d need to pass in   event    FORGOT PASSWORD   to match the  name   value   An other option  assuming you want the write and read json values to be the same      More Info   There is  yet  another way to manage the serialization and deserialization process with Jackson   You can specify these annotations to use your own custom serializer and deserializer    JsonSerialize using   MySerializer class   JsonDeserialize using   MyDeserializer class  public final class MyClass               Then you have to write MySerializer and MyDeserializer which look like this   MySerializer  public final class MySerializer extends JsonSerializer lt MyClass gt         Override     public void serialize final MyClass yourClassHere  final JsonGenerator gen  final SerializerProvider serializer  throws IOException  JsonProcessingException                  here you d write data to the stream with gen write      methods            MyDeserializer  public final class MyDeserializer extends org codehaus jackson map JsonDeserializer lt MyClass gt         Override     public MyClass deserialize final JsonParser parser  final DeserializationContext context  throws IOException  JsonProcessingException                  then you d do something like parser getInt   or whatever to pull data off the parser         return null             Last little bit  particularly for doing this to an enum JsonEnum that serializes with the method getYourValue    your serializer and deserializer might look like this   public void serialize final JsonEnum enumValue  final JsonGenerator gen  final SerializerProvider serializer  throws IOException  JsonProcessingException       gen writeString enumValue getYourValue        public JsonEnum deserialize final JsonParser parser  final DeserializationContext context  throws IOException  JsonProcessingException       final String jsonValue   parser getText        for  final JsonEnum enumValue   JsonEnum values                  if  enumValue getYourValue   equals jsonValue                         return enumValue                      return null

User · Answer

I did it like this      Your JSON   quot event quot   quot forgot password quot       Your class to map  public class LoggingDto        JsonProperty value    quot event quot       private FooEnum logType       Your enum public enum FooEnum        DATA LOG   quot Dummy 1 quot        DATA2 LOG   quot Dummy 2 quot        DATA3 LOG   quot forgot password quot        DATA4 LOG   quot Dummy 4 quot        DATA5 LOG   quot Dummy 5 quot        UNKNOWN   quot  quot         private String fullName       FooEnum String fullName            this fullName   fullName             public String getFullName             return fullName              JsonCreator     public static FooEnum getLogTypeFromFullName String fullName            for  FooEnum logType   FooEnum values                  if  logType fullName equals fullName                     return logType                                  return UNKNOWN             So the value of the property  quot logType quot  for class LoggingDto will be DATA3 LOG

User · Answer

The simplest way I found is using  JsonFormat Shape OBJECT annotation for the enum    JsonFormat shape   JsonFormat Shape OBJECT  public enum MyEnum

User · Answer

In the context of an enum  using  JsonValue now  since 2 0  works for serialization and deserialization   According to the jackson-annotations javadoc for  JsonValue      NOTE  when use for Java enums  one additional feature is that value returned by annotated method is also considered to be the value to deserialize from  not just JSON String to serialize as  This is possible since set of Enum values is constant and it is possible to define mapping  but can not be done in general for POJO types  as such  this is not used for POJO deserialization    So having the Event enum annotated just as above works  for both serialization and deserialization  with jackson 2 0

User · Answer

The serializer   deserializer solution pointed out by  xbakesx is an excellent one if you wish to completely decouple your enum class from its JSON representation   Alternatively  if you prefer a self-contained solution  an implementation based on  JsonCreator and  JsonValue annotations would be more convenient   So leveraging on the example by  Stanley the following is a complete self-contained solution  Java 6  Jackson 1 9    public enum DeviceScheduleFormat        Weekday      EvenOdd      Interval       private static Map lt String  DeviceScheduleFormat gt  namesMap   new HashMap lt String  DeviceScheduleFormat gt  3        static           namesMap put  weekday   Weekday           namesMap put  even-odd   EvenOdd           namesMap put  interval   Interval               JsonCreator     public static DeviceScheduleFormat forValue String value            return namesMap get StringUtils lowerCase value                JsonValue     public String toValue             for  Entry lt String  DeviceScheduleFormat gt  entry   namesMap entrySet                  if  entry getValue      this                  return entry getKey                       return null     or fail

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