Database Access - Java - page 729

Java annotations always appear directly before their target. The @Id (and many other prop-
erty annotations) can appear either on the field (e.g., private int id ) or on the get method
( getId() ), never on the set method. Within a given project, JPA requires you to be consist-
ent: either use field annotations or method annotations, but not both.

There are many annotations, and a full treatment of them is book-length, so consult any good
book on JPA or Hibernate for details.

Once you have annotated your entity classes, and created a bit of XML configuration, you
need to write code using either the JPA or Hibernate APIs to actually load or save data (see
Ian's Basic Steps: JPA ) .

Example 18-1 uses JPA to persist a simple entity object.

Example 18-1. JPASimple
public public class class JPASimple JPASimple {

@SuppressWarnings ( "unchecked" )
public

public static static void void main ( String [] args ) {

System . out . println ( "JPASimple.main()" );

EntityManagerFactory entityMgrFactory = null null ;

EntityManager entityManager = null null ;

try try {

entityMgrFactory = Persistence . createEntityManagerFactory ( "jpademo" );
entityManager = entityMgrFactory . createEntityManager ();

EntityTransaction transaction = entityManager . getTransaction ();
transaction . begin ();

// Create an entity in the database.
Person np = new new Person ( "Tom" , "Boots" );

System . out . println ( np );
entityManager . persist ( np );
transaction . commit ();

int int id = np . getId ();

System . out . println ( "Created Person with Id " + id );

transaction = entityManager . getTransaction ();
transaction . begin ();

Query query = entityManager . createQuery (