Support custom countSpec in SimpleJpaRepository.findAll(…).

Closes #3727

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/JpaSpecificationExecutor.java

@@ -38,6 +38,7 @@ import org.springframework.lang.Nullable;
  * @author Christoph Strobl
  * @author Diego Krupitza
  * @author Mark Paluch
+ * @author Joshua Chen
  */
 public interface JpaSpecificationExecutor<T> {
 
@@ -71,6 +72,21 @@ public interface JpaSpecificationExecutor<T> {
 	 */
 	Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable);
 
+	/**
+	 * Returns a {@link Page} of entities matching the given {@link Specification}.
+	 * <p>
+	 * Supports counting the total number of entities matching the {@link Specification}.
+	 * <p>
+	 *
+	 * @param spec can be {@literal null}, if no {@link Specification} is given all entities matching {@code <T>} will be
+	 *          selected.
+	 * @param countSpec can be {@literal null}，if no {@link Specification} is given all entities matching {@code <T>} will
+	 *          be counted.
+	 * @param pageable must not be {@literal null}.
+	 * @return never {@literal null}.
+	 */
+	Page<T> findAll(@Nullable Specification<T> spec, @Nullable Specification<T> countSpec, Pageable pageable);
+
 	/**
 	 * Returns all entities matching the given {@link Specification} and {@link Sort}.
 	 * <p>

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java

@@ -100,6 +100,7 @@ import org.springframework.util.Assert;
  * @author Ernst-Jan van der Laan
  * @author Diego Krupitza
  * @author Seol-JY
+ * @author Joshua Chen
  */
 @Repository
 @Transactional(readOnly = true)
@@ -456,10 +457,15 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 
 	@Override
 	public Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable) {
+		return findAll(spec, spec, pageable);
+	}
+
+	@Override
+	public Page<T> findAll(@Nullable Specification<T> spec, @Nullable Specification<T> countSpec, Pageable pageable) {
 
 		TypedQuery<T> query = getQuery(spec, pageable);
 		return pageable.isUnpaged() ? new PageImpl<>(query.getResultList())
-				: readPage(query, getDomainClass(), pageable, spec);
+				: readPage(query, getDomainClass(), pageable, countSpec);
 	}
 
 	@Override