In the last tutorial a number of Java objects were created and the values persisted to the various database tables under the management of Hibernate. Now, we will create a very simple test program to load the data back from the database and display it to the console.<\/p>\n
We can do this by choosing one Person object and iterating over all the associated objects that it contains.<\/p>\n
<\/p>\n
The following code will show the effect of Hibernate re-constituting objects from the database.<\/p>\n
[code lang=”Java”]
\npackage alphastar.main;<\/p>\n
import java.util.Iterator;
\nimport java.util.Set;<\/p>\n
import org.hibernate.Session;
\nimport org.hibernate.Transaction;<\/p>\n
import alphastar.model.Person;
\nimport alphastar.model.Stock;
\nimport alphastar.model.StockEvent;<\/p>\n
public class ReadStock {<\/p>\n
public void process() {
\nTransaction txn = null;
\nSession session = HibernateUtil.getSessionFactory().openSession();
\ntxn = session.beginTransaction();
\ntry {
\n\/\/ get a Person by id
\nObject a = session.get(Person.class, new Integer(2));
\nPerson p = (Person)a;
\nSystem.out.println(“Name: “+p.getName());<\/p>\n
Iterator i = p.getStocksHeld().iterator();
\nwhile (i.hasNext()) {
\nObject o = i.next();
\nStock stock = (Stock)o;
\nSystem.out.println(“Code: “+stock.getCode());
\nSystem.out.println(“Name: “+stock.getName());
\n\/\/ Iterate over all the stockheld instances<\/p>\n
Set stockEvents = stock.getStockEvents();
\nIterator i2 = stockEvents.iterator();
\nwhile (i2.hasNext()) {
\nObject o2 = i2.next();
\nStockEvent se = (StockEvent) o2;
\nSystem.out.println(“Buy Date: “+se.getBuyDate());
\nSystem.out.println(“Buy Price: “+se.getBuyPrice());
\nSystem.out.println(“Sold Date: “+se.getSoldDate());
\nSystem.out.println(“Sold Price: “+se.getSoldPrice());
\nSystem.out.println(“—————-“);
\n}
\n}<\/p>\n
txn.commit();
\n\/\/session.close();
\n} catch (RuntimeException e) {
\nif(session.getTransaction() != null){
\nsession.getTransaction().rollback();
\n}
\ne.printStackTrace();
\n} finally{
\nsession.flush();
\nsession.close();
\n}
\n}<\/p>\n
}<\/p>\n
[\/code]<\/p>\n
As seen above, we select a Person id (in this example we choose 2, which is a PK (idperson) to the Person table. The intersting part is that a top level object with object references to other classes are automatically loaded in one go.
\nSo from loading the Person object (only) we were given the associated Stock objects, and from the Stock objects, the StockEvent objects were loaded.<\/p>\n