Centralized EntityManager definition

Sda2/P/forum_1/src/main/java/de/hdm_stuttgart/mi/sda2/forum/Register.java

@@ -5,7 +5,6 @@ import java.sql.SQLException;
 
 import javax.persistence.EntityManager;
 
-import com.vaadin.addon.jpacontainer.JPAContainerFactory;
 import com.vaadin.data.Property.ValueChangeListener;
 import com.vaadin.data.fieldgroup.FieldGroup.CommitException;
 import com.vaadin.navigator.Navigator;
@@ -31,13 +30,8 @@ public class Register extends CustomComponent implements View, ValidateGlobal {
 	private static final long serialVersionUID = -1309958813377546099L;
 	public final static String viewId = Register.class.getCanonicalName();
 
-	final static EntityManager em;
-
-	static {
-		em = JPAContainerFactory.createEntityManagerForPersistenceUnit(
-				PersistenceHelper.getPersistenceUnitName());
-	}
-
+	private transient EntityManager em = PersistenceHelper.getEntityManager();
+	
 	final Button cancelButton = new Button("Cancel"), okButton = new Button(
 			"OK");
 

Sda2/P/forum_1/src/main/java/de/hdm_stuttgart/mi/sda2/forum/tools/PersistenceHelper.java

 package de.hdm_stuttgart.mi.sda2.forum.tools;
 
+import javax.persistence.EntityManager;
+
+import com.vaadin.addon.jpacontainer.JPAContainerFactory;
+
 public class PersistenceHelper {
 	
 	private final static String persistenceUnitName = "de.hdm_stuttgart.mi.sda2.forum";
 	
+	private static EntityManager em = null;
 	/**
 	 * Hard coded so far
 	 * @return The persistence unit's name as being defined in
 	 *   ../resources/META-INF/persistence.xml 
 	 */
-	public static String getPersistenceUnitName() {
+	private static String getPersistenceUnitName() {
 		return persistenceUnitName;
 	}
+	
+	
+	public static EntityManager getEntityManager() {
+		if (null == em) {
+			em = JPAContainerFactory.createEntityManagerForPersistenceUnit(
+					PersistenceHelper.getPersistenceUnitName());
+		}
+		return em;
+	}
 
 }