In this exercise, I do not want to use any container such as Spring or Glassfish. I am deploying my application to Tomcat. I only use JPA. What I want to achieve is to follow best practices and OOP concepts correctly, and a good separation of concerns and layering.
I have a database table like this:
mysql> DESCRIBE book;
+-------------+--------------+------+-----+---------+
| Field | Type | Null | Key | Default |
+-------------+--------------+------+-----+---------+
| isbn | varchar(13) | NO | PRI | NULL |
| name | varchar(64) | NO | UNI | NULL |
| publishDate | date | YES | | NULL |
| price | decimal(8,2) | YES | | NULL |
| publisher | varchar(6) | YES | MUL | NULL |
+-------------+--------------+------+-----+---------+
and here is my Entity:
@Entity
@Table(name = "book")
public class Book {
@Id
private String isbn;
@Basic
private String name;
@Basic
private Date publishDate;
@Basic
private double price;
@Basic
private String publisher;
// Getters, Setters...
This is my PersistenceUtil class:
package biz.tugay.books10Aug.dao;
/* User: [email protected] Date: 10/08/15 Time: 22:22 */
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class PersistenceUtil {
private static EntityManagerFactory entityManagerFactory;
public static void initalizeEntityManagerFactory() {
if (entityManagerFactory == null || !entityManagerFactory.isOpen()) {
entityManagerFactory = Persistence.createEntityManagerFactory("bookshop");
}
}
public static EntityManagerFactory getEntityManagerFactory() {
return entityManagerFactory;
}
public static EntityManager getEntityManager() {
if (entityManagerFactory == null || !entityManagerFactory.isOpen()) {
initalizeEntityManagerFactory();
}
EntityManager entityManager = entityManagerFactory.createEntityManager();
return entityManager;
}
public static void closeEntityManagerFactory() {
entityManagerFactory.close();
}
}
and in my web application I have a ContextListener:
package biz.tugay.books10Aug.web;
/* User: [email protected] Date: 10/08/15 Time: 22:24 */
import biz.tugay.books10Aug.dao.PersistenceUtil;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
@WebListener
public class BookShopServletContextListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
PersistenceUtil.initalizeEntityManagerFactory();
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
PersistenceUtil.closeEntityManagerFactory();
}
}
#1 Is this the right way to initialise Persistence Context? Or should this be responsibility of DAO / Service classes?
My DAO Layer:
package biz.tugay.books10Aug.dao;
/* User: [email protected] Date: 10/08/15 Time: 22:50 */
import biz.tugay.books10Aug.model.Book;
public interface BookDao {
public void persist(Book book);
public Book getWithIsbn(String isbn);
}
and the implementation:
package biz.tugay.books10Aug.dao;
/* User: [email protected] Date: 10/08/15 Time: 22:54 */
import biz.tugay.books10Aug.model.Book;
import javax.persistence.EntityManager;
public class BookDaoImpl implements BookDao {
private EntityManager entityManager;
public BookDaoImpl(EntityManager entityManager) {
this.entityManager = entityManager;
}
@Override
public void persist(Book book) {
entityManager.persist(book);
}
@Override
public Book getWithIsbn(String isbn) {
Book book = entityManager.find(Book.class, isbn);
return book;
}
}
#2 Is it ok that the DAO Layer requires an EntityManager and assumes that its transaction has already begun? Should it be the DAOs responsibility to obtain the EntityManager and/or begin/commit transaction?
Here is my Service Layer:
package biz.tugay.books10Aug.service;
/* User: [email protected] Date: 11/08/15 Time: 00:12 */
import biz.tugay.books10Aug.model.Book;
import java.util.Date;
public interface BookService {
public void createBook(String isbn, String name, Date publishDate, double price, String publisher);
public Book getWithIsbn(String isbn);
}
and the implementation:
package biz.tugay.books10Aug.service;
/* User: [email protected] Date: 11/08/15 Time: 00:12 */
import biz.tugay.books10Aug.dao.BookDao;
import biz.tugay.books10Aug.dao.BookDaoImpl;
import biz.tugay.books10Aug.dao.PersistenceUtil;
import biz.tugay.books10Aug.model.Book;
import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;
import java.util.Date;
public class BookServiceImpl implements BookService {
private BookDao bookDao;
private EntityManager entityManager;
public BookServiceImpl() {
EntityManager entityManager = PersistenceUtil.getEntityManager();
bookDao = new BookDaoImpl(entityManager);
this.entityManager = entityManager;
}
@Override
public void createBook(String isbn, String name, Date publishDate, double price, String publisher) {
Book book = new Book();
book.setIsbn(isbn);
book.setName(name);
book.setPublishDate(publishDate);
book.setPrice(price);
book.setPublisher(publisher);
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
bookDao.persist(book);
transaction.commit();
}
@Override
public Book getWithIsbn(String isbn) {
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
Book withIsbn = bookDao.getWithIsbn(isbn);
transaction.commit();
return withIsbn;
}
}
#3 Again, I have the same questions on my mind. Is this class a mess like this? It does not have any dependencies, it obtains its EntityManager from the PersistenceUtil class in the Constructor. Is this ok? How about the entityManager field and starting / committing transactions which surrounds DAO calls?
And finally I have a view like this:
<form action="<c:url value="/book"/>" method="post">
<label for="isbn">
isbn:
</label>
<input type="text" name="isbn" id="isbn"/>
<input type="submit"/>
</form>
and a Servlet:
@WebServlet(urlPatterns = "/book")
public class BookServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
BookService bookService = new BookServiceImpl();
String isbn = req.getParameter("isbn");
Book withIsbn = bookService.getWithIsbn(isbn);
req.setAttribute("book", withIsbn);
req.getRequestDispatcher("/isbn.jsp").forward(req,resp);
}
}
#4 Is it ok that the Servlet initialises a Service object for each call? Or should it have a private static Service object?(I think not, but I am not sure thus asking..)
As I said, (just for learning purposes) I want to make such a basic web app which is maintainable and which follows OOP principles, without using any other frameworks such as Spring.