Book hash IDs: consider potential hash collisions; move logic into

BookEventHandler

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

Author: Fincer

bookstore/src/main/java/com/fjordtek/bookstore/model/book/BookEventHandler.java

@@ -31,6 +31,12 @@ public class BookEventHandler {
 	private BookHashRepository bookHashRepository;
 
 	/*
+	 * Generate hash id for the book. One-to-one unidirectional tables.
+	 * Associate generated book hash object information
+	 * to the book (table).
+	 * Associate new book object information
+	 * to the book hash (table).
+	 *
 	 * When using REST API to add a new book, we need to add a corresponding
 	 * book hash Id to BOOK_HASH table, as well.
 	 *
@@ -42,6 +48,23 @@ public class BookEventHandler {
 	@HandleAfterCreate
 	public void handleAfterCreate(Book book) {
 		BookHash bookHash = new BookHash();
+
+		/*
+		 * In a very unlikely scenario, we have hash collisions
+		 * (same hash values generated for two different book entity objects).
+		 * Therefore, we need to check that hash id is not already defined for
+		 * some other book.
+		 */
+		int i = 0;
+		while (i < 5) {
+			if (bookHashRepository.findByHashId(bookHash.getHashId()) != null) {
+				bookHash = new BookHash();
+			} else {
+				break;
+			}
+			i++;
+		}
+
 		book.setBookHash(bookHash);
 		bookHash.setBook(book);
 

bookstore/src/main/java/com/fjordtek/bookstore/web/BookController.java

@@ -31,6 +31,7 @@
 
 import com.fjordtek.bookstore.model.book.AuthorRepository;
 import com.fjordtek.bookstore.model.book.Book;
+import com.fjordtek.bookstore.model.book.BookEventHandler;
 import com.fjordtek.bookstore.model.book.BookHash;
 import com.fjordtek.bookstore.model.book.BookHashRepository;
 import com.fjordtek.bookstore.model.book.BookRepository;
@@ -81,6 +82,9 @@ public void initBinder(WebDataBinder binder) {
 	@Autowired
 	private BookAuthorHelper     bookAuthorHelper;
 
+	@Autowired
+	private BookEventHandler     bookEventHandler;
+
 /*
 	private Map<String,String> globalModelMap = new HashMap<String,String>() {
 		private static final long serialVersionUID = 1L;
@@ -211,26 +215,12 @@ public String webFormSaveNewBook(
 
 		httpServerLogger.log(requestData, responseData);
 
-		/*
-		 * Generate hash id for the book. One-to-one unidirectional tables.
-		 * Associate generated book hash object information
-		 * to the book (table).
-		 * Associate new book object information
-		 * to the book hash (table).
-		 */
-		BookHash bookHash = new BookHash();
-		book.setBookHash(bookHash);
-		bookHash.setBook(book);
-
-		/*
-		 * More sophisticated methods are required to handle
-		 * user input with random letter cases etc. considered
-		 */
-		//authorRepository.save(book.getAuthor());
 		bookAuthorHelper.detectAndSaveUpdateAuthorForBook(book);
 
 		bookRepository.save(book);
-		bookHashRepository.save(bookHash);
+
+		// Manually call a book event handler. Is there a better way to do this?
+		bookEventHandler.handleAfterCreate(book);
 
 		return "redirect:" + env.getProperty("page.url.list");
 	}