Implement FindBooksUseCase with FindBooksPort interface

src/main/java/catalogservice/application/FindBooksPort.java

@@ -0,0 +1,8 @@
+package catalogservice.application;
+
+import catalogservice.domain.Book;
+import io.reactivex.Flowable;
+
+public interface FindBooksPort {
+  Flowable<Book> books();
+}

src/main/java/catalogservice/application/FindBooksUseCase.java

@@ -1,8 +1,17 @@
 package catalogservice.application;
 
+import catalogservice.domain.Book;
+import io.reactivex.Flowable;
+import lombok.RequiredArgsConstructor;
+
 import javax.inject.Singleton;
 
 @Singleton
+@RequiredArgsConstructor
 public class FindBooksUseCase {
+  private final FindBooksPort findBooksPort;
 
-}
+  public Flowable<Book> invoke() {
+    return findBooksPort.books();
+  }
+}

src/main/java/catalogservice/domain/Book.java

@@ -0,0 +1,20 @@
+package catalogservice.domain;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@AllArgsConstructor
+@NoArgsConstructor
+@Data
+public class Book {
+  private String title;
+  private String author;
+  private String additionalAuthors;
+  private String isbn;
+  private String isbn13;
+  private Integer numberOfPages;
+  private Integer yearPublished;
+  private Integer originalPublicationYear;
+  private Long goodreadsBookId;
+}