Implement Page and PageResponseType for QueryBus

As a user of the QueryBus/QueryGateway the use case where you’d want to retrieve a Page<E> of a certain type makes sense. We should hence introduce a Page implementation which can be used as a ResponseType (introduced in #463) when performing a query.

[manuelarte]

Hi,

I also implemented my own PageResponseType, it is not at all ready for production, but maybe it can give some inspiration to someone in the same situation:

public class PageResponseType<R> extends AbstractResponseType<Page<R>> {


  /**
   * Instantiate a {@link ResponseType} with the given {@code expectedResponseType} as the type to be matched against and
   * to which the query response should be converted to, as is or as the contained type for an array/list/etc.
   *
   * @param expectedResponseType the response type which is expected to be matched against and to be returned, as is or as
   *                             the contained type for an array/list/etc
   */
  @JsonCreator
  @ConstructorProperties({"expectedResponseType"})
  public PageResponseType(@JsonProperty("expectedResponseType") Class<R> expectedResponseType) {
    super(expectedResponseType);
  }

  @Override
  public boolean matches(Type responseType) {
    Type unwrapped = ReflectionUtils.unwrapIfType(responseType, Future.class, Page.class);
    return isGenericAssignableFrom(unwrapped) || isAssignableFrom(unwrapped);
  }

  @Override
  public Page<R> convert(Object response) {
    return (Page<R>) response;
  }

  @Override
  public Class responseMessagePayloadType() {
    return Page.class;
  }

  @Override
  public String toString() {
    return "PageResponseType{" + expectedResponseType + "}";
  }

}

[rhubarb]

Excellent @manuelarte! I’m curious why you think it’s not production-ready? It works like a charm.

Just to complete the story for others finding this: I used manuelarte’s code above, verbatim, with these imports in my class: (notice that the Page is a spring JPA page)

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.axonframework.common.ReflectionUtils;
import org.axonframework.messaging.responsetypes.AbstractResponseType;
import org.axonframework.messaging.responsetypes.ResponseType;
import org.springframework.data.domain.Page;

import java.beans.ConstructorProperties;
import java.lang.reflect.Type;
import java.util.concurrent.Future;

My query class has a get/setPageable() method on it to hold the pageable that comes in from the Spring REST controller. My query service code looks a bit like this:

        // Create a simple query pojo with a single property to carry the pageable from my Spring REST controller
        final PaginatedSummariesQuery query = new PaginatedSummariesQuery(pageable);

        // use manuelarte's magic response-type to carry a page across the query bus
        final ResponseType<Page<SummaryEntity>> responseType = new PageResponseType<>(SummaryEntity.class);
        final CompletableFuture<Page<BookSummaryEntity>> resultFuture = queryGateway.query(query, responseType);
        try {
            Page<SummaryEntity> entityPage = resultFuture.get();
            return entityPage;
        } catch (InterruptedException | ExecutionException e) {
            throw new ResourceNotFoundException("BookSummary", "query");
        }

and my query handler mostly like this (verbose for clarity)

    @QueryHandler
    public Page<SummaryEntity> handle(PaginatedSummariesQuery query) {
        final Page<SummaryEntity> page = repository.findAll(query.getPageable());
        return page;
    }