Hi Venkatesch, I did also modify the orginal persistence.xml so that is exactly the same as my example to be able to run Main.java directly without the ant script.
So in both cases I'm not using the build.xml file anymore. The only difference I see is that one version runs the other not. Best egards, Lars 2008/3/12, Addanki, Venkatesh <[EMAIL PROTECTED]>: > > Lars, > > One obvious difference between your code and the out of box sample is > the way the driver class and its properties are specified. build.xml vs > persistence.xml. It looks like the org.apache.derby.jdbc.EmbeddedDriver > class from your persistence.xml is not being found or the connection url > is not getting through. > > Regards > > V > > > > -----Original Message----- > From: Lars Vogel [mailto:[EMAIL PROTECTED] > Sent: Wednesday, March 12, 2008 9:22 AM > To: [email protected] > Subject: JPA - Null pointer exception > > Hi, > > I trying to make JPA work for me. The delivered example works without > problems, I can also successfully modify this example. The example was > based on http://openjpa.apache.org/quick-start.html. > > But if I create a new project the Entity Manager returns only a NULL > value. > Error: > > Exception in thread "main" java.lang.NullPointerException > at hellojpa.Main.main(Main.java:44) > > > I use the same files as in the working example. All jars are included in > the build path. I assume that the persistence.xml is not found but to my > knowledge the classpath is correctly maintained. The path .../bin > contains the directory META-INF and here the file persistence.xml. > > Any advice? I must be missing something very simple but cannot figure it > out. For example coding please see below. > > Best regards, Lars > > File structure: > > src > - hellojpa > - Main.java > - Message.java > - META-INF > - persistence.xml > > Same structure in the bin directory. > > > -----------persistence.xml.............. > > <?xml version="1.0" encoding="UTF-8"?> > <!-- > Licensed to the Apache Software Foundation (ASF) under one > or more contributor license agreements. See the NOTICE file > distributed with this work for additional information > regarding copyright ownership. The ASF licenses this file > to you under the Apache License, Version 2.0 (the > "License"); you may not use this file except in compliance > with the License. You may obtain a copy of the License at > > http://www.apache.org/licenses/LICENSE-2.0 > > Unless required by applicable law or agreed to in writing, > software distributed under the License is distributed on an > "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY > KIND, either express or implied. See the License for the > specific language governing permissions and limitations > under the License. > --> > <persistence xmlns="http://java.sun.com/xml/ns/persistence"; > xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; version="1.0"> > > <!-- > A persistence unit is a set of listed persistent entities as > well > the configuration of an EntityManagerFactory. We configure each > example in a separate persistence-unit. > --> > <persistence-unit name="hellojpa" > transaction-type="RESOURCE_LOCAL"> > <!-- > The default provider can be OpenJPA, or some other product. > This element is optional if OpenJPA is the only JPA provider > in the current classloading environment, but can be > specified > in cases where there are multiple JPA implementations > available. > --> > > <provider> > org.apache.openjpa.persistence.PersistenceProviderImpl > </provider> > > > <!-- We must enumerate each entity in the persistence unit --> > <class>hellojpa.Message</class> > > <properties> > <property name="openjpa.ConnectionURL" > > value="jdbc:derby:C:/DerbyDatabases/hellojpa-database5;create=true" /> > <property name="openjpa.ConnectionDriverName" > value="org.apache.derby.jdbc.EmbeddedDriver" /> > <property name="openjpa.ConnectionUserName" value="" /> > <property name="openjpa.ConnectionPassword" value="" /> > > <!-- > Tell OpenJPA to automatically create tables in the > database > for entities. Note that this should be disabled when > running against a production database, since you > probably > don't want to be altering the schema at runtime. > --> > <property name="openjpa.jdbc.SynchronizeMappings" > value="buildSchema" /> > > </properties> > </persistence-unit> > > </persistence> > > > -----------Main.java > > /* > * Licensed to the Apache Software Foundation (ASF) under one > * or more contributor license agreements. See the NOTICE file > * distributed with this work for additional information > * regarding copyright ownership. The ASF licenses this file > * to you under the Apache License, Version 2.0 (the > * "License"); you may not use this file except in compliance > * with the License. You may obtain a copy of the License at > * > * http://www.apache.org/licenses/LICENSE-2.0 > * > * Unless required by applicable law or agreed to in writing, > * software distributed under the License is distributed on an > * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY > * KIND, either express or implied. See the License for the > * specific language governing permissions and limitations > * under the License. > */ > package hellojpa; > > import java.util.*; > import javax.persistence.*; > > > /** > * A very simple, stand-alone program that stores a new entity in the > * database and then performs a query to retrieve it. > */ > public class Main { > > @SuppressWarnings("unchecked") > public static void main(String[] args) { > System.out.println(System.getProperty("java.class.path")); > // Create a new EntityManagerFactory using the System > properties. > // The "hellojpa" name will be used to configure based on the > // corresponding name in the META-INF/persistence.xml file > EntityManagerFactory factory = Persistence. > createEntityManagerFactory("hellojpa", > System.getProperties()); > > // Create a new EntityManager from the EntityManagerFactory. The > // EntityManager is the main object in the persistence API, and > is > // used to create, delete, and query objects, as well as access > // the current transaction > EntityManager em = factory.createEntityManager(); > > // Begin a new local transaction so that we can persist a new > entity > em.getTransaction().begin(); > > // Create and persist a new Message entity > em.persist(new Message("Hello Persistence!")); > > // Commit the transaction, which will cause the entity to > // be stored in the database > em.getTransaction().commit(); > > // It is always good practice to close the EntityManager so that > // resources are conserved. > em.close(); > > // Create a fresh, new EntityManager > EntityManager em2 = factory.createEntityManager(); > > // Perform a simple query for all the Message entities > Query q = em2.createQuery("select m from Message m"); > > // Go through each of the entities and print out each of their > // messages, as well as the date on which it was created > for (Message m : (List<Message>) q.getResultList()) { > System.out.println(m.getMessage() > + " (created on: " + m.getCreated() + ")"); > } > > // Again, it is always good to clean up after ourselves > em2.close(); > factory.close(); > } > } > > ----------- >
