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POGlassfish JPA: Problems injecting EntityManager
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  1. POGlassfish JPA: Problems injecting EntityManager
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    copied!<p>I am new to Java EE. I tried to get some first examples running (JPA). I am using Glassfish v3. The trouble is that I don't get the App Server injecting the EntityManager. Hear is one example <a href="http://www.adam-bien.com/roller/abien/entry/ejb_3_persistence_jpa_for" rel="nofollow noreferrer">http://www.adam-bien.com/roller/abien/entry/ejb_3_persistence_jpa_for</a> which I extended with a JSP client.</p> <p>Entity:</p> <pre><code> package beans; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; @Entity public class Book { @Id @GeneratedValue private Long id; private String title; private String subtitle; public Book() { } public Book(String title) { this.title = title; } } </code></pre> <p>BookService Interface:</p> <pre><code> package beans; import javax.ejb.Local; @Local public interface BookService { Book createOrUpdate(Book book); void remove(Book book); Book find(Object id); } </code></pre> <p>BookServiceBean:</p> <pre><code> package beans; import javax.ejb.Stateless; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; @Stateless public class BookServiceBean implements BookService { @PersistenceContext private EntityManager em; public Book createOrUpdate(Book book) { return em.merge(book); } public void remove(Book book) { em.remove(em.merge(book)); } public Book find(Object id) { return em.find(Book.class, id); } } </code></pre> <p>persistence.xml:</p> <pre><code>&lt;persistence&gt; &lt;persistence-unit name="sample" transaction-type="JTA"&gt; &lt;jta-data-source&gt;jdbc/MarcelsDataSource&lt;/jta-data-source&gt; &lt;properties&gt; &lt;property name="eclipselink.ddl-generation" value="create-tables"/&gt; &lt;/properties&gt; &lt;/persistence-unit&gt; &lt;/persistence&gt; </code></pre> <p>index.jsp:</p> <pre><code>&lt;%@ page import="beans.BookServiceBean" %&gt; &lt;%@ page import="beans.Book" %&gt; &lt;html&gt; &lt;body&gt; &lt;% BookServiceBean bs = new BookServiceBean(); Book b = new Book("Superman"); bs.createOrUpdate(b); %&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>If I run the example I get a java.lang.NullPointerException in the createOrUpdate() method so the entityManager is obviously not injected correctly. I tried to find a remedy for days now and some help would be highly appreciated. </p> <p>Thanks</p> <p>Marcel </p>
 

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