Error after applying metadata (with category) on page

Question

I have created a metadata schema which has a dropdown field referring to a particular catrgory. When I apply the metadata on page and publish the page, I get internal server error.

Error message:

2015-09-05 04:00:44,039 ERROR JSONSerializer - Error deserializing. com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of org.dd4t.contentmodel.Category, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information at [Source: {"RevisionDate":"2015-09-05T13:00:27.693","Filename........ ..................................................................... .......................................................................... ; line: 1, column: 17721] (through reference chain: org.dd4t.contentmodel.impl.PageImpl["Categories"]->java.util.ArrayList[0])

When I apply similar metadata on Structure Group, the pages work fine.

I am passing the values of these metadata schemas to GenerateSitemap TBB. Do I need to use any special data-type for category and keywords? Currently I am using string and navigation.json is formed correctly.

We are using java DXA.

Update:

This issue also occurs on pages which do not have navigation. So I suspect its not related to sitempap TBB or navigation

Answer 1

This was a bug in the dd4t-2 beta stack. Since you are using (probably?) a mixed set of DXA-Java and a dd4t-2 stack, I'm not sure where it should be fixed.

In any case, the actual fix is in org.dd4t.contentmodel.PageImpl:

// change this line:

@JsonProperty("Categories")
private List categories;

// Into this line:

@JsonProperty("Categories") @JsonDeserialize(contentAs = CategoryImpl.class)
private List categories;