Gson: @Expose vs @SerializedName

Question

With respect to Gson what is the difference between @Expose and @SerializedName("stringValue")?

Answer 1

Even if it's late I wanted to answer this question. To explain it we must know what is serialization and deserialization. serialization is converting object into json string and deserialization is converting json string into object.

Let's say we've User class with no annotations.

public class User{
    private String userName;
    private Integer userAge;

    public User(String name, Integer age){
        userName = name;
        userAge = age;
    }
}

And we serialize this object as below

User user = new User("Ahmed", 30);
Gson gson = new Gson();
String jsonString = gson.toJson(user);

Json string will be like this

{
    "userName":"Ahmed",
    "userAge":30
}

If we add annotation @SerializedName

public class User{

    @SerializedName("name")
    private String userName;
    @SerializedName("age")
    private Integer userAge;

    public User(String name, Integer age){
        userName = name;
        userAge = age;
    }
}

Json string will be like this

{
    "name":"Ahmed",
    "age":30
}

@Expose is used to allow or disallow serialization and deserialization. @Expose is optional and it has two configuration parameters: serialize and deserialize. By default they're set to true. To serialize and deserialize with @Expose we create gson object like this

Gson gsonBuilder = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();

Below userName won't be deserialized. userName's value will be null.

@SerializedName("name")
@Expose(deserialize = false)
private String userName;

Below userName won't be serialized.

@SerializedName("name")
@Expose(serialize = false)
private String userName;

Json string will be like this. Only userAge will be deserialized.

{
    "age":30
}

Answer 2

@SerializeName is used to set the key that json object will include ,however @Expose is used to decide whether the variable will be exposed for Serialisation and Deserialisation ,or not. Here's the documentation of @Expose.

Answer 3

class Person{
String name;
String password;
}

suppose if i put i annotation Expose on top of a variable name or password without SerializedName, it will be serialized AS variable name

But if we put SerializedName like ("username") or ("password"),they will be serialized with that key

if Serialized

{"username":"trinadh","password":"hello"}

if not

{"name":"trinadh","password":"hello"}

Answer 4

Moreover, @Expose comes with two boolean flags: deserialize and serialize, to allow skipping the field for one phase.