类com.restfb.types.Post声明了多个名为type的JSON字段

Question

我正在尝试将rest-facebook响应转换为Post类对象，如下所示:

Post post = gson.fromJson(restFBResponse.toString(), Post.class);

式中，restFBResponse为来自Facebook的帖子。但是它会导致错误:

Exception in thread "main" java.lang.IllegalArgumentException: class com.restfb.types.Post declares multiple JSON fields named type

我认为这是由于:

1)
class Post extends NamedFacebookType{
  @Facebook
  private String type;
  //and some more class members
}
2)
class NamedFacebookType extends FacebookType {
  //few class members
}
3)
class FacebookType implements Serializable {
  @Facebook
  private String type;
  //and some more class members
}

因此，private String type;在class Post和class FacebookType中被声明了两次。

1)如果这种重新声明发生在子类中，它不应该被重写吗?和

2)我如何克服这个错误class com.restfb.types.Post declares multiple JSON fields named type

Answer 1

我刚刚编写了自己的类，没有扩展，没有其他更好的选择。

public class MyPost{
    @Facebook
    private String type;
    public String getType() {
        return type;
    }
    public void setType(String type) {
        this.type = type;
    }
}

Answer 2

我猜GSON建议

@SerializedName(类型1)private String类型;

这可能解决问题。但我认为应该有一个更清晰的解决方案，我发现这个问题已被标记为无效，没有收到进一步的回应。

Answer 3

您可以为gson编写自己的序列化器和反序列化器来序列化和反序列化Post对象。

使用restfb的DefaultJsonMapper来映射Post对象

,

private Gson gson = new GsonBuilder()
        .serializeNulls()
        .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
        .registerTypeAdapter(Post.class, new PostDeserializer())
        .registerTypeAdapter(Post.class, new PostSerializer())
        .setPrettyPrinting()
        .create();
private DefaultJsonMapper dMapper = new DefaultJsonMapper();
private class PostDeserializer implements JsonDeserializer<Post> {
        @Override
        public Post deserialize(JsonElement jsonElement, Type type,
                JsonDeserializationContext context) throws JsonParseException {
            Post post = dMapper.toJavaObject(jsonElement.toString(), Post.class);
            return post;
        }
    }
private class PostSerializer implements JsonSerializer<Post> {
        @Override
        public JsonElement serialize(Post post, Type type,
                JsonSerializationContext context) {
            return gson.toJsonTree(dMapper.toJson(post));
        }
    }

Answer 4

您不希望在类Post中声明相同的变量"type"。当它从FacebookType扩展时，它隐式地具有变量"type"。

解决方案:

Simply remove the sentence "private String type;" from your Post class
Replace the "private" word with "protected" in your "type" variable from your FacebookType