La persistenza dei dati è una caratteristica fondamentale di ogni applicazione, e quasi sempre la scelta ricade sull’utilizzo di un database relazionale. Java, fin dalle sue prime versioni, ha avuto a disposizione la libreria JDBC per accedere a tale tipo di database. In questa presentazione si mostrerà come utilizzare la libreria JDBC, mostrandone pregi e limiti. In seguito si mostrerà l’utilizzo tradizionale di Hibernate, forse il più famoso e diffuso degli Object/Relational Mapper (ORM), che permettono di trattare i dati relazionali inserendoli all’interno di oggetti. Infine si introdurrà la Java Persistence API (JPA), la libreria di persistenza ORM introdotta con la Java Enterprise Edition (JEE) 5.

1. Java e i database: da JDBC a JPA
Lucio Benfante
lucio@benfante.com
verona.javaday.it www.jugpadova.it

2. database...chi era costui?

3. The database and the applications
database
Application 1 Application 3
Application 2
Atomicity
another
Consistency db
Isolation
Durability

4. Relational databases
person city
id first_name last_name father born_in id name
n 1 Lucio Benfante 101 n 1
101 Venezia
2 Giacomo Puccini 3 102 born_in_city
102 Lucca
3 Michele Puccini 102
4 Antonio Puccini 2 103 103 Milano
0
father
The term relational database was
originally defined and coined by
Edgar Codd at IBM Almaden
Research Center in 1970.

5. SQL: Structured Query Language
SELECT first_name, last_name FROM person
WHERE last_name = 'Puccini'
ORDER BY first_name;
INSERT INTO person VALUES (5, 'Mario', 'Rossi', NULL, NULL);
UPDATE person SET first_name = 'Carlo' WHERE id = 1;
DELETE FROM person WHERE id = 1;
...and much more, included Data Definition Language (DDL).

6. Relational
Database Management Systems (DBMS)
Informix
DB2 Dynamic Server
(just a small selection)
specific
DBMS
protocol
Application DBMS

7. Java DataBase Connectivity
(JDBC)
Application
JDBC API
PostgreSQL Oracle
JDBC Driver JDBC Driver
PostgreSQL Oracle
DBMS DBMS
protocol protocol
PostgreSQL Oracle
DBMS DBMS

8. JDBC
Getting a connection
Class.forName("org.postgresql.Driver" );
Connection con =
DriverManager.getConnection (
“jdbc:postgresql://localhost/javaday”,
“username”, “password”);

9. JDBC
Executing an SQL statement
PreparedStatement ps = con.prepareStatement(
"SELECT * FROM Person WHERE last_name=?”);
ps.setString(1, "Puccini");
ResultSet rs = ps.executeQuery();

10. JDBC
Retrieving your data
while ( rs.next() ) {
String firstName = rs.getString(“first_name”);
String lastName = rs.getString(“last_name”);
long fatherId = rs.getLong(“father”);
...etc.etc....
}

11. JDBC
All together
Connection con=null;
try {
Class.forName( "com.mioDbms.mioDriver" );
con = DriverManager.getConnection (
“jdbc:...”, “user”, “pass”);
PreparedStatement ps = con.prepareStatement(
"SELECT * FROM Person WHERE name=?”);
ps.setString(1, "Lucio Benfante");
ResultSet rs = ps.executeQuery();
while ( rs.next() ) { rs.getString...ecc..ecc.... }
rs.close();
ps.close();
stmt.close();
} catch(Exception e){ ...
} finally {
try {
If (con != null) { con.close(); }
} catch( Exception ignoreMe ) {}
}

12. Object Relational Mapping (ORM)
ORM

13. Hibernate
Mapping with XML
<class name="Person" table="PERSON">
<id name="id" column="ID">
<generator class="native"/>
</id>
<property name="firstName" column=”FIRST_NAME”/>
<property name="lastName" column=”LAST_NAME”/>
<many-to-one name=”father”
column=”FATHER”/>
<many-to-one name=”bornIn”
column=”BORN_IN”
class=”City”/>
</class>

14. Hibernate
Getting your objects
SessionFactory sf =
new Configuration().configure().buildSessionFactory();
Session session = sf.openSession();
Transaction tx = session.beginTransaction();
Query q = session.createQuery(
“from Person p where p.lastName = :lastName”);
q.setString(“lastName”, “Puccini”);
List people = q.list();
// here you'll have a list of persistent Person objects
Person person = ((Person)people.get(0))
City city = person.getBornIn();
person.setFirstName(“Pippo”);
tx.commit();
session.close();
sf.close();

15. Hibernate
Creating new records
Session session = sf.openSession();
Transaction tx = session.beginTransaction();
Person person = new Person(“Lucio”, “Benfante”);
session.save(person);
tx.commit();
session.close();

16. Hibernate
Configuration
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">org.postgresql.Driver</property>
<property name="connection.url">jdbc:postgresql://localhost/javaday</property>
<property name="connection.username">username</property>
<property name="connection.password">password</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<!-- Create/Update the database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<mapping resource="com/myproject/Person.hbm.xml"/>
<mapping resource="com/myproject/City.hbm.xml"/>
</session-factory>
</hibernate-configuration>

17. Look at our layers now
Application ●Hibernate
●iBatis
●JPA
ORM
− Hibernate
− Toplink Essentials
JDBC API − EclipseLink
PostgreSQL Oracle
− OpenJPA
JDBC Driver JDBC Driver ...
●
PostgreSQL Oracle
DBMS DBMS
protocol protocol
PostgreSQL Oracle
DBMS DBMS

18. Java Persistence API (JPA)
A standard ORM in Java Enterprise Edition (JEE5)

19. JPA
Mapping with annotations
@Entity
public class Person implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Basic(optional = false)
private Integer id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
@JoinColumn(name = "born_in", referencedColumnName = "id")
@ManyToOne
private City bornIn;
@OneToMany(mappedBy = "father")
private Collection<Person> children;
@JoinColumn(name = "father", referencedColumnName = "id")
@ManyToOne
private Person father;
// ... normal getters and setters
// equals and hashCode implementation
}

20. Hibernate
or
JPA?

21. References
● www.hibernate.org
● http://java.sun.com/docs/books/tutorial/jdbc/index.html
● http://java.sun.com/javaee/5/docs/tutorial/doc/
● “Java Persistence with Hibernate”, Christian Bauer
and Gavin King, Manning, 2007
● www.parancoe.org