Android-GSON+改造中的继承和抽象类

Question

我有以下类层次结构

public abstract class SyncModel {
    @Expose
    @SerializedName("id")
    private Long globalId;

    @Expose
    protected DateTime lastModified;
    
    /* Constructor, methods... */
}

public class Event extends SyncModel {
    @Expose
    private String title;
    
    /* Other fields, constructor, methods... */
}

public interface EventAPI {
    @POST("/event/create")
    void sendEvent(@Body Event event, Callback<Long> cbEventId);
}

改装日志：

D   Retrofit    ---> HTTP POST http://hostname:8080/event/create
D   Retrofit    Content-Type: application/json; charset=UTF-8
D   Retrofit    Content-Length: 297
D   Retrofit    {"title":"Test Event 01",...,"id":null,"lastModified":"2015-07-09T14:17:08.860+03:00"}
D   Retrofit    ---> END HTTP (297-byte body)

但是当我在请求参数中发布事件实例时，只有抽象类被序列化。

改型Java接口：

@FormUrlEncoded
@POST("/event/create")
void sendEvent(@Field("event") Event event, Callback<Long> cbEventId);

D   Retrofit    ---> HTTP POST http://hostname:8080/event/create
D   Retrofit    Content-Type: application/x-www-form-urlencoded; charset=UTF-8
D   Retrofit    Content-Length: 101
D   Retrofit    event=SyncModel%28globalId%3Dnull%2C+lastModified%3D2015-07-09T13%3A36%3A33.510%2B03%3A00%29
D   Retrofit    ---> END HTTP (101-byte body)

我还注意到，在第二种情况下，globalid字段序列化名称是globalid，但它应该是id！这使我认为改型对@field使用的GSONConverter与对@body参数使用的GSONConverter不同...

分级依赖关系

compile 'com.squareup.retrofit:retrofit:1.9.+'
compile 'com.squareup.okhttp:okhttp:2.3.+'
compile 'net.danlew:android.joda:2.8.+'
compile ('com.fatboyindustrial.gson-jodatime-serialisers:gson-jodatime-serialisers:1.1.0') {  // GSON + Joda DateTime
    exclude group: 'joda-time', module: 'joda-time'
}

REST客户端

public final class RESTClient {

    // Not a real server URL
    public static final String SERVER_URL = "http://hostname:8080";

    // one-time initialization
    private static GsonBuilder builder = new GsonBuilder()
            .serializeNulls()
            .excludeFieldsWithoutExposeAnnotation()
            .setDateFormat("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'SSS'Z'");
    // Joda DateTime type support
    private static Gson gson = Converters.registerDateTime(builder).create();

    private static RestAdapter restAdapter = new RestAdapter.Builder()
            .setLogLevel(RestAdapter.LogLevel.FULL)     // for development
            .setEndpoint(SERVER_URL)
            .setConverter(new GsonConverter(gson))    // custom converter
            .build();

    private static final EventAPI eventService = restAdapter.create(EventAPI.class);
    /* + Getter for eventService */

    static {
        // forget them
        restAdapter = null;
        gson = null;
        builder = null;
    }

}

RESTClient.getEventService().sendEvent(event, new Callback<Long>() {/* ... */});

Answer 1

请查看@field的文档。上面写着：

使用String#valueof(Object)将值转换为字符串，然后对表单URL进行编码。

String#valueof(Object)调用内部的对象#ToString()。我假设您的syncModel有ToString()方法，而event没有。当翻新调用String.ValueOf(event)时，将调用SyncModel#ToString()而不是event#ToString()。这就是为什么在改装日志中看不到title的原因。

在转换@field参数时，Gson根本不起任何作用。但也可以--您可以使toString()方法看起来如下所示：

@Override
public String toString() {
    return GsonProvider.getInstance().toJson(this);
}

将它放在抽象的syncmodel类中，它也可以用于event。