Use new projection capabilities in Spring Data Hopper.

Uses interfaces instead of DTOs to implement projections. Works
around DATAJPA-864 [0].

[0] https://jira.spring.io/browse/DATAJPA-864

spring-boot-samples/spring-boot-sample-data-jpa/src/main/java/sample/data/jpa/domain/HotelSummary.java

@@ -16,48 +16,15 @@
 
 package sample.data.jpa.domain;
 
-import java.io.Serializable;
-import java.math.BigDecimal;
-import java.math.MathContext;
-import java.math.RoundingMode;
+public interface HotelSummary {
 
-public class HotelSummary implements Serializable {
+	City getCity();
 
-	private static final long serialVersionUID = 1L;
+	String getName();
 
-	private static final MathContext MATH_CONTEXT = new MathContext(2,
-			RoundingMode.HALF_UP);
+	Double getAverageRating();
 
-	private final City city;
-
-	private final String name;
-
-	private final Double averageRating;
-
-	private final Integer averageRatingRounded;
-
-	public HotelSummary(City city, String name, Double averageRating) {
-		this.city = city;
-		this.name = name;
-		this.averageRating = averageRating == null ? null
-				: new BigDecimal(averageRating, MATH_CONTEXT).doubleValue();
-		this.averageRatingRounded = averageRating == null ? null
-				: (int) Math.round(averageRating);
-	}
-
-	public City getCity() {
-		return this.city;
-	}
-
-	public String getName() {
-		return this.name;
-	}
-
-	public Double getAverageRating() {
-		return this.averageRating;
-	}
-
-	public Integer getAverageRatingRounded() {
-		return this.averageRatingRounded;
+	default Integer getAverageRatingRounded() {
+		return getAverageRating() == null ? null : (int) Math.round(getAverageRating());
 	}
 }

spring-boot-samples/spring-boot-sample-data-jpa/src/main/java/sample/data/jpa/domain/RatingCount.java

@@ -16,26 +16,9 @@
 
 package sample.data.jpa.domain;
 
-import java.io.Serializable;
+public interface RatingCount {
 
-public class RatingCount implements Serializable {
+	Rating getRating();
 
-	private static final long serialVersionUID = 1L;
-
-	private final Rating rating;
-
-	private final long count;
-
-	public RatingCount(Rating rating, long count) {
-		this.rating = rating;
-		this.count = count;
-	}
-
-	public Rating getRating() {
-		return this.rating;
-	}
-
-	public long getCount() {
-		return this.count;
-	}
+	long getCount();
 }

spring-boot-samples/spring-boot-sample-data-jpa/src/main/java/sample/data/jpa/service/HotelRepository.java

@@ -16,13 +16,13 @@
 
 package sample.data.jpa.service;
 
-import java.util.List;
-
 import sample.data.jpa.domain.City;
 import sample.data.jpa.domain.Hotel;
 import sample.data.jpa.domain.HotelSummary;
 import sample.data.jpa.domain.RatingCount;
 
+import java.util.List;
+
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.Query;
@@ -32,11 +32,11 @@ interface HotelRepository extends Repository<Hotel, Long> {
 
 	Hotel findByCityAndName(City city, String name);
 
-	@Query("select new sample.data.jpa.domain.HotelSummary(h.city, h.name, avg(r.rating)) "
+	@Query("select h.city as city, h.name as name, avg(r.rating) as averageRating "
 			+ "from Hotel h left outer join h.reviews r where h.city = ?1 group by h")
 	Page<HotelSummary> findByCity(City city, Pageable pageable);
 
-	@Query("select new sample.data.jpa.domain.RatingCount(r.rating, count(r)) "
+	@Query("select r.rating as rating, count(r) as count "
 			+ "from Review r where r.hotel = ?1 group by r.rating order by r.rating DESC")
 	List<RatingCount> findRatingCounts(Hotel hotel);
 }