DAO can't get call and get Nullpointer exception?

[Nakataa Kokuyo]

Good day,

I'm new in JPA and i have below class intend to save a record, it is running @onetoone relationship between student and contact class, When i do a test run and i got nullpointerexception error on line 13 under Studentanager.class, appreciated your enlightenment.

P/S : Suspect missing out some implementation, hope someone can guide me out here, caused the Entity Manager always Null.

StudentManager class :

public class StudentManager {

		private final Log logger = LogFactory.getLog(getClass());
		
		
		private StudentDAO dao;
		
		public void doInsertStudent(Student tempStudent, Contact tempContact){
			if(tempStudent!= null){
				tempStudent.setContact(tempContact);
				dao=(StudentDAO) new StudentDAOImpl();				
				logger.info("tempStudent name=="+tempStudent.getName()); //manage to show name
				dao.createRecord(tempStudent); // show error java.lang.NullPointerException
			}
		}
}

StudentDAOImpl class :

public class StudentDAOImpl extends GenericDAOImpl<Student> implements StudentDAO{

}

public abstract class GenericDAOImpl<T> implements GenericDAO<T> {

@PersistenceContext(unitName="myTest")
	protected EntityManager em;

	private Class<T> type;

	public GenericDAOImpl() {

		Type t = getClass().getGenericSuperclass();		
        ParameterizedType pt = (ParameterizedType) t;        
        type = (Class) pt.getActualTypeArguments()[0];
        
	}

...
	public T createRecord(final T t) {
		this.em.persist(t);
		return t;
	}
}

Persistence.xml reside in META-INF folder

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
             version="2.0">

<persistence-unit name="myTest" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.school.dao.GenericDAOImpl</class>

<properties>
<property name="hibernate.hbm2ddl.auto" value="create"/>
<property name="hibernate.archive.autodetection" value="class, hbm"/>
<property name="hibernate.show_sql" value="true"/>
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
<property name="hibernate.connection.url" value="jdbc:mysql://localhost/myDB"/>
<property name="hibernate.connection.username" value="xx"/>
<property name="hibernate.connection.password" value="xx"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
<property name="hibernate.c3p0.min_size" value="5"/>
<property name="hibernate.c3p0.max_size" value="20"/>
<property name="hibernate.c3p0.timeout" value="300"/>
<property name="hibernate.c3p0.max_statements" value="50"/>
<property name="hibernate.c3p0.idle_test_period" value="3000"/>
</properties>
</persistence-unit>

</persistence>

My Test case :

public static void main(String[] args) {
		
		Student student = new Student ();
		student .setStudent _Id("Danny123");
		student .setName("Danny");
		
		Contact contact = new Contact();
		contact.setName("Contact1 name");
		
		System.out.println("student name="+ student .getName());
		System.out.println("Contact name="+ contact.getName());
		
		StudentManager p1 = new StudentManager();
		p1.doInsertStudent(student, contact);

	}

[Nakataa Kokuyo]

Just in case in future someone having similar issue, this can be resolve by using ClassPathXmlApplicationContext if you do not using jUnit for the testing.

final AbstractApplicationContext context = new ClassPathXmlApplicationContext(
				"/applicationContext.xml");
		
TestStudent t1 = (TestStudent ) context.getBean("TestStudentManager");