Solr-java error: class com.restfb.types.Post decla

问题:

I'm trying to convert rest-facebook response to a Post class object as follows:

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

where, restFBResponse is a post from Facebook. But it is resulting into error:

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

I think this is due to:

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
}

So, private String type; is being declared twice, in class Post and class FacebookType.

1) If such re-declaration occurs in subclass,should it not be overridden? and

2) How can I overcome this error class com.restfb.types.Post declares multiple JSON fields named type?

回答1:

I just written my own class without extension, found no other better option..

public class MyPost{

    @Facebook
    private String type;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }
}

回答2:

I guess GSON suggested that

@SerializedName("type1") private String type;

This may resolve issue. But I think there should be a cleaner solution to this..I found that the issue has been marked invalid and no further response was received.

回答3:

You can write your own serializer and deserializer for gson to serialize and deserialize Post object.

While doing so use restfb's DefaultJsonMapper to map Post ob.

Something Like,

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));
        }
    }

回答4:

You don't want to declare the same variable "type" in your class Post. As it extends from FacebookType, it implicitly has the variable "type".

Solution:

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