Can I use jackson mixIns to modify "getters" behavior?

Question

I'm in the need of do some clean up of some invisible characters (\r\n) and html tags for specific getters on my entities.

I've been trying to use mixIns to modify what's returned from the entity but I'm not sure how can I reference the target class in my MixIn so I can add the clean up logic there. From the my tests seems that not even my method is called.

This is what I have so far, but it never gets called

public abstract class BookMixIn {
@JsonProperty
public String getTitle() {
    return StringUtils.deleteWhitespace(getTitle());
}
}

public class Book {
    private String title;
    // getter/setters omitted...
}

And the ObjectMapper config:

mapper.getSerializationConfig().addMixInAnnotations(com.company.Book.class, 
                                                    com.company.BookMixIn.class);  
mapper.configure(SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS, false);  
String tmp = mapper.writeValueAsString(book);
log.info(tmp);

Can this be accomplished via MixIns?

Thanks

Answer 1

Jackson mix-ins are purely for associating annotations; they are not used for adding behavior (code). So they would not help you here.

But the simple way that would work (possibly using mix-in too) is to add annotation for using custom serializer, which can use whatever filtering is needed:

@JsonSerialize(using=MyCoolSerializer.class) public String getTitle() { }

so either add that to POJO, if possible; but if not, associate it using mix-in.

Answer 2

If you are running Jackson 1.9, this works:

BookCleaner cleanBook = new BookCleaner(book);
mapper.getSerializationConfig().addMixInAnnotations(Book.class, BookMixIn.class);
mapper.writeValueAsString(cleanBook);

@JsonSerialize
class BookCleaner {
    private Book book;

    public BookCleaner(final Book book) { this.book = book; }

    @JsonUnwrapped
    public Book getBook() { return book; }

    @JsonProperty("title") 
    public String getCleanTitle() { return cleanup(getBook().getTitle()); }
}

public interface BookMixIn {
    @JsonIgnore public String getTitle();
}