Java e i database: da JDBC a JPA

Java e i database: da JDBC a JPA
Lucio Benfante
lucio@benfante.com

verona.javaday.it www.jugpadova.it

The database and the applications

database

Application 1 Application 3

Application 2
Atomicity
another
Consistency db
Isolation
Durability

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.

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).

Relational
Database Management Systems (DBMS)

Informix
DB2 Dynamic Server

(just a small selection)

specific
DBMS
protocol
Application DBMS

Java DataBase Connectivity
(JDBC)

Application

JDBC API
PostgreSQL Oracle
JDBC Driver JDBC Driver

PostgreSQL Oracle
DBMS DBMS
protocol protocol

PostgreSQL Oracle
DBMS DBMS

JDBC
Getting a connection

Class.forName("org.postgresql.Driver" );

Connection con =
DriverManager.getConnection (
“jdbc:postgresql://localhost/javaday”,
“username”, “password”);

JDBC
Executing an SQL statement

PreparedStatement ps = con.prepareStatement(
"SELECT * FROM Person WHERE last_name=?”);

ps.setString(1, "Puccini");

ResultSet rs = ps.executeQuery();

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....
}

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 ) {}
}

Object Relational Mapping (ORM)

ORM

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>

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();

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();

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>

<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>

<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>

<property name="show_sql">true</property>

<property name="hbm2ddl.auto">update</property>

<mapping resource="com/myproject/Person.hbm.xml"/>
<mapping resource="com/myproject/City.hbm.xml"/>
</session-factory>
</hibernate-configuration>

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

Java Persistence API (JPA)

A standard ORM in Java Enterprise Edition (JEE5)

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
}

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

Java e i database: da JDBC a JPA

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