Multiple GSON @SerializedName per field?

问题:

Is there any way in Gson to map multiple JSON fields to a single Java object member variable?

Let's say I have a Java class...

public class MyClass {
    String id;
    String name;
}

I want to use this single class with two different services. However, these two services differ in how they return their data...

{ "id": 2341, "person": "Bob" }

... and ...

{ "id": 5382, "user": "Mary" }

... respectively.

Is there any way to map both the "person" and "user" fields in the JSON string to the name field in the Java object?

(Note: I only ever need to convert from JSON string to Java object - never the other way around.)

回答1:

In October 2015, Gson version 2.4 (changelog) added the ability to use alternate/multiple names for @SerializedName when deserializing. No more custom TypeAdapter needed!

Usage:

@SerializedName(value="name", alternate={"person", "user"})

https://google.github.io/gson/apidocs/com/google/gson/annotations/SerializedName.html

回答2:

It is not supported to define multiple @SerializedName annotations to a field at Gson.

Reason: By default Deserialization is managed with a LinkedHashMap and the keys are defined by incoming json's field names (not the custom class's field names or the serializedNames) and there is a one to one mapping. You can see the implementation(how deserialization works) at ReflectiveTypeAdapterFactory class's inner class Adapter<T>'s read(JsonReader in) method.

Solution: You can write a custom TypeAdapter which handles name, person and user json tags and maps them to name field of your custom class MyClass:

class MyClassTypeAdapter extends TypeAdapter<MyClass> {

    @Override
    public MyClass read(final JsonReader in) throws IOException {
        final MyClass myClassInstance = new MyClass();

        in.beginObject();
        while (in.hasNext()) {
            String jsonTag = in.nextName();
            if ("id".equals(jsonTag)) {
                myClassInstance.id = in.nextInt();
            } else if ("name".equals(jsonTag) 
                    || "person".equals(jsonTag)
                    || "user".equals(jsonTag)) {
                myClassInstance.name = in.nextString();
            }
        }
        in.endObject();

        return myClassInstance;
    }

    @Override
    public void write(final JsonWriter out, final MyClass myClassInstance)
            throws IOException {
        out.beginObject();
        out.name("id").value(myClassInstance.id);
        out.name("name").value(myClassInstance.name);
        out.endObject();
    }
}

Test case:

    String jsonVal0 = "{\"id\": 5382, \"user\": \"Mary\" }";
    String jsonVal1 = "{\"id\": 2341, \"person\": \"Bob\"}";

    final GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeAdapter(MyClass.class, new MyClassTypeAdapter());
    final Gson gson = gsonBuilder.create();

    MyClass myClassInstance0 = gson.fromJson(jsonVal0, MyClass.class);
    MyClass myClassInstance1 = gson.fromJson(jsonVal1, MyClass.class);

    System.out.println("jsonVal0 :" + gson.toJson(myClassInstance0));
    // output: jsonVal0 :{"id":5382,"name":"Mary"}

    System.out.println("jsonVal1 :" + gson.toJson(myClassInstance1));
    // output: jsonVal1 :{"id":2341,"name":"Bob"}

Examples about TypeAdapters.

Edit 2016.04.06 : As @Mathieu Castets has written at his answer, it is supported now. (That is the correct answer for this question.)

public abstract String[] alternate
Returns: the alternative names of the field when it is deserialized
Default: {}

回答3:

for Kotlin fans

@SerializedName(value="name", alternate= ["person", "user"])

回答4:

For KOTLIN i used below but doesn't work

@SerializedName(value="name", alternate= ["person", "user"])

so i edited it and here it works fine!!

@SerializedName(value="name", alternate= arrayOf("person", "user"))