When is the JsonProperty property used and what is it used for

Question

This bean  State     public class State        private boolean isSet        JsonProperty  isSet       public boolean isSet             return isSet              JsonProperty  isSet       public void setSet boolean isSet            this isSet   isSet             is sent over the wire using the ajax   success  callback             success   function response                  if response State isSet                      alert  success called successfully                  Is the annotation  JsonProperty required here   What is the advantage of using it   I think I can remove this annotation without causing any side effects   Reading about this annotion on https   github com FasterXML jackson-annotations wiki Jackson-Annotations I don t know when this is required to be used

User · Accepted Answer

Here s a good example  I use it to rename the variable because the JSON is coming from a  Net environment where properties start with an upper-case letter   public class Parameter      JsonProperty  Name     public String name     JsonProperty  Value     public String value       This correctly parses to from the JSON    Parameter       Name   Parameter-Name      Value   Parameter-Value

User · Answer

As you know  this is all about serialize and desalinize an object  Suppose there is an object   public class Parameter     public String  name    public String  value       The serialization of this object is         name              value             The name of variable is directly used to serialize data  If you are about to remove system api from system implementation  in some cases  you have to rename variable in serialization deserialization   JsonProperty is a meta data to tell serializer how to serial object  It is used to    variable name access  READ  WRITE  default value required optional   from example   public class Parameter      JsonProperty          value  Name           required true          defaultValue  No name           access  Access READ WRITE    public String  name     JsonProperty          value  Value           required true          defaultValue  Empty           access  Access READ WRITE    public String  value

User · Answer

well for what its worth now    JsonProperty is ALSO used to specify getter and setter methods for the variable apart from usual serialization and deserialization  For example suppose you have a payload like this        check   true     and a Deserializer class   public class Check       JsonProperty  check         It is needed else Jackson will look got getCheck method and will fail   private Boolean check     public Boolean isCheck          return check          Then in this case JsonProperty annotation is neeeded  However if you also have a method in the class   public class Check         JsonProperty  check      Not needed anymore   private Boolean check     public Boolean getCheck          return check          Have a look at this documentation too   http   fasterxml github io jackson-annotations javadoc 2 3 0 com fasterxml jackson annotation JsonProperty html

User · Answer

From JsonProperty javadoc       Defines name of the logical property  i e  JSON object field name to use for the property  If value is empty String  which is the default   will try to use name of the field that is annotated

User · Answer

As addition to other answers   JsonProperty annotation is really important if you use the  JsonCreator annotation in classes which do not have a no-arg constructor   public class ClassToSerialize        public enum MyEnum           FIRST SECOND THIRD            public String stringValue    ABCD       public MyEnum myEnum         JsonCreator     public ClassToSerialize MyEnum myEnum            this myEnum   myEnum             public static void main String   args  throws IOException           ObjectMapper mapper   new ObjectMapper             ClassToSerialize classToSerialize   new ClassToSerialize MyEnum FIRST           String jsonString   mapper writeValueAsString classToSerialize           System out println jsonString           ClassToSerialize deserialized   mapper readValue jsonString  ClassToSerialize class           System out println  StringValue      deserialized stringValue           System out println  MyEnum      deserialized myEnum             In this example the only constructor is marked as  JsonCreator  therefore Jackson will use this constructor to create the instance  But the output is like      Serialized    stringValue   ABCD   myEnum   FIRST        Exception in   thread  main    com fasterxml jackson databind exc InvalidFormatException  Can not   construct instance of   ClassToSerialize MyEnum   from String value  stringValue   value not one of declared Enum   instance names   FIRST  SECOND  THIRD    But after the addition of the  JsonProperty annotation in the constructor    JsonCreator public ClassToSerialize  JsonProperty  myEnum   MyEnum myEnum        this myEnum   myEnum      The deserialization is successful      Serialized    myEnum   FIRST   stringValue   ABCD        StringValue  ABCD      MyEnum  FIRST

User · Answer

Adding the JsonProperty also ensures safety in case someone decides they want to change one of the property names not realizing the class in question will be serialized to a Json object  If they change the property name the JsonProperty ensures it will be used in the Json object  and not the property name

User · Answer

Without annotations  inferred property name  to match from JSON  would be  set   and not -- as seems to be the intent --  isSet   This is because as per Java Beans specification  methods of form  isXxx  and  setXxx  are taken to mean that there is logical property  xxx  to manage

User · Answer

I think OldCurmudgeon and StaxMan are both correct but here is one sentence answer with simple example for you    JsonProperty name   tells Jackson ObjectMapper to map the JSON property name to the annotated Java field s name     example of json that is submitted   Car       Type   Ferrari        where it gets mapped  public static class Car      JsonProperty  Type     public String type

User · Answer

In addition to all the answers above  don t forget the part of the documentation that says      Marker annotation that can be used to define a non-static method as a    setter  or  getter  for a logical property  depending on its   signature   or non-static object field to be used  serialized    deserialized  as a logical property    If you have a non-static method in your class that is not a conventional getter or setter then you can make it act like a getter and setter by using the annotation on it  See the example below   public class Testing       private Integer id      private String username       public Integer getId             return id             public void setId Integer id            this id   id             public String getUsername             return username             public void setUsername String username            this username   username             public String getIdAndUsername             return id         username              public String concatenateIdAndUsername             return id         username             When the above object is serialized  then response will contain    username from getUsername    id from getId    idAndUsername from getIdAndUsername     Since the method getIdAndUsername starts with get then it s treated as normal getter hence  why you could annotate such with  JsonIgnore    If you have noticed the concatenateIdAndUsername is not returned and that s because it name does not start with get and if you wish the result of that method to be included in the response then you can use  JsonProperty        and it would be treated as normal getter setter as mentioned in the above highlighted documentation

[java] When is the @JsonProperty property used and what is it used for?

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