{"id":16223,"date":"2013-08-09T15:03:16","date_gmt":"2013-08-09T12:03:16","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=16223"},"modified":"2018-09-26T15:09:21","modified_gmt":"2018-09-26T12:09:21","slug":"java-ee-stateful-session-bean-ejb-example","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2013\/08\/java-ee-stateful-session-bean-ejb-example.html","title":{"rendered":"Java EE Stateful Session Bean (EJB) example"},"content":{"rendered":"

In this article we are going to see how you can use Stateful Session Beans to keep track of state across a client Session in a simple Web Application.<\/p>\n

1. Introduction<\/h2>\n

Stateful Session Beans usually hold information about a specific client’s session, and holds that information throughout the whole session (opposed to Stateless Session Beans). A Stateful EJB instance is coupled with only one client. One client can of course have many EJB instances is his session.<\/p>\n

In this example we are going to create a simple Shopping Cart application. The session bean will hold a list of products. As the client adds more products to his cart, this list will grow accordingly. Finally the client will be able to checkout his order and the products on the aforementioned list will be persisted in a MySQL database.<\/p>\n

To implement the above functionality,\u00a0we are going to create an EAR Project and an EJB Project that will host our Session Bean and a Dynamic Web Application that will host a Servlet, testing the aforementioned behavior. We are going to use Eclipse Java EE IDE 4,3 Kepler and Glassfish 4.0 as our container. Additionally we are going to use standard JPA 2.o to persist our products in a MySQL\u00a05.6.14 database running on localhost. Here is a guide on how to Integrate MySQL with Glassfish<\/a>.<\/p>\n

2. Create a new Enterprise Application Project<\/h2>\n

Create a new Enterprise Application Project named\u00a0StatefulEJBEAR<\/code>\u00a0. In Eclipse IDE select File -> New -> Enterprise Application Project, fill in the form and click Finish:<\/p>\n

\"new-ear-project\"<\/a><\/p>\n

3. Create a new EJB Projet<\/h2>\n

Create a new EJB Project called StatefulSessionBeansEJB<\/code>. We are going to create our session bean on this. Go to File -> New -> EJB Project and fill out the form. Be careful to select \u201cAdd EAR Project\u201d and Select \u201cStatefulEJBEAR<\/code>\u201d as EAR project name:<\/p>\n

\"new-ejb-project\"<\/a><\/p>\n

4. Create a Stateful Session Bean<\/h2>\n

Open StatefulSessionBeansEJB<\/code> Project in the Project Explorer and in the folder\u00a0ejbModule<\/code>\u00a0create a new source package named com.javacodegeeks.enterprise.ejb<\/code>. In that package create a new Interface<\/code> that will be a local view of the EJB:<\/p>\n

Cart.java:<\/span><\/em><\/p>\n

package com.javacodegeeks.enterprise.ejb;\r\n\r\nimport javax.ejb.Local;\r\n\r\nimport com.javacodegeeks.enterprise.product.Product;\r\n\r\n@Local\r\npublic interface Cart {\r\n\r\n\t  void addProductToCart(Product product);\r\n\r\n\t  void checkOut();\r\n\r\n}<\/pre>\n
As you can see, we declare two methods, one to add a product to the cart and another to checkout the order.<\/p>\n
And here is the Session Bean:<\/p>\n
CartBean.java:<\/span><\/em><\/p>\n
package com.javacodegeeks.enterprise.ejb;\r\n\r\nimport java.util.ArrayList;\r\nimport java.util.List;\r\nimport java.util.concurrent.TimeUnit;\r\n\r\nimport javax.annotation.PostConstruct;\r\nimport javax.ejb.Stateful;\r\nimport javax.ejb.StatefulTimeout;\r\nimport javax.ejb.TransactionAttribute;\r\nimport javax.ejb.TransactionAttributeType;\r\nimport javax.persistence.EntityManager;\r\nimport javax.persistence.PersistenceContext;\r\n\r\nimport com.javacodegeeks.enterprise.product.Product;\r\n\r\n@Stateful\r\n@StatefulTimeout(unit = TimeUnit.MINUTES, value = 20)\r\npublic class CartBean implements Cart {\r\n\r\n\t@PersistenceContext(unitName = \"pu\", type = PersistenceContextType.EXTENDED)\r\n\tprivate EntityManager entityManager;\r\n\r\n\tprivate List products;\r\n\r\n\t@PostConstruct\r\n\tprivate void initializeBean(){\r\n\t   products = new ArrayList<>();\r\n\t}\r\n\r\n\t@Override\r\n\tpublic void addProductToCart(Product product) {\r\n\t\t products.add(product);\r\n\r\n\t}\r\n\r\n\t@Override\r\n\t@TransactionAttribute(TransactionAttributeType.REQUIRED)\r\n\tpublic void checkOut() {\r\n\t\tfor(Product product : products){\r\n\t\t\tentityManager.persist(product);\r\n\t\t}\r\n\t\tproducts.clear();\r\n\r\n\t}\r\n}<\/pre>\n
As you can see, our Session bean implements our Cart<\/code> interface and simply holds a List of products (more on class Product<\/code> later).<\/p>\n
In the above code notice:<\/p>\n