Home >> Hibernate
Interceptors can be used in cases where we may require
some sort of callback methods called just before the
actual operation is called. For example If it is required
to log any perticular SQL in some different log/audit file,
then we can set a simple Interceptor like CaptureSQL or
LogSQL, just while opening Sesson using SessionFactory
openSession (Interceptor) method.
Following sample interceptor does the logging of SQL
on prepare statement.
import org.apache.log4j.Logger;
import org.hibernate.EmptyInterceptor;
public class CaptureSQL extends EmptyInterceptor {
private static Logger log = Logger.getLogger("L1");
public String onPrepareStatement(String sql) {
log.debug("Loging SQL statement ...... start");
log.debug(sql);
log.debug("Loging SQL statement ...... end");
return sql;
}
}
|
CaptureSQL is the user defined class that extends
org.hibernate.EmptyInterceptor to become receiving
callback overridden method, such as
"onPrepareStatement", when ever a Session is opened,
by calling
SessionFactory.openSession(new CaptureSQL()).
Appropriate log4j.properties file should be configured
to be able to handle these logging part. My sample log4j.properties
file is as follows:
log4j.rootLogger=DEBUG
log4j.logger.L1=INHERIT, L
log4j.appender.L=org.apache.log4j.FileAppender
log4j.appender.L.file=sample.txt
log4j.appender.L.layout=org.apache.log4j.PatternLayout
log4j.appender.L.layout.ConversionPattern=%d [%t] %C{1} - %m%n
|
And the Client code is as follows:
Client.java (Hibernate one to one mapping Test main class)
// This source is provided on "AS IS" basis.
import java.util.Calendar;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.apache.log4j.Logger;
public class Client {
private static final SessionFactory sessionFactory;
static {
try {
// Create the SessionFactory from hibernate.cfg.xml
sessionFactory = new Configuration().configure().buildSessionFactory();
} catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
public static void createRecord()
{
Session session = getSessionFactory().openSession(new CaptureSQL());
Transaction trx = session.beginTransaction();
trx.begin();
Car car = new Car();
car.setCarName("My Car1");
car.setModel("My Model1");
car.setSegment("My Segment1");
session.persist(car);
trx.commit();
session.close();
}
/**
* @param args
*/
public static void main(String[] args) {
createRecord();
}
}
|
hibernate.cfg.xml (configuration file for creation of Hibernate session factory)
// This source is provided on "AS IS" basis.
<?xml version='1.0' encoding='utf-8'?>
<!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.hsqldb.jdbcDriver
</property>
<property name="connection.url">
jdbc:hsqldb:hsql://localhost/
</property>
<property name="connection.username">sa</property>
<property name="connection.password"></property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">
org.hibernate.dialect.HSQLDialect
</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">
thread
</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<mapping resource="car.hbm.xml"/>
</session-factory>
</hibernate-configuration>
|
This example domain class "Car.java" file is as follows:
// This source is provided on "AS IS" basis.
public class Car {
private String carName;
private String model;
private String segment;
public String getCarName() {
return carName;
}
public void setCarName(String carName) {
this.carName = carName;
}
public String getModel() {
return model;
}
public void setModel(String model) {
this.model = model;
}
public String getSegment() {
return segment;
}
public void setSegment(String segment) {
this.segment = segment;
}
}
|
And the corresponding Hibernate HBM configuration file is as follows:
// This source is provided on "AS IS" basis.
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Car" table="Car">
<id name="carName" access="property" column="car_name"/>
<property name="model" column="car_model"/>
<property name="segment" column="car_segment"/>
</class>
</hibernate-mapping>
|
In order to execute this example, you may have to create relevant table
(the DDL as shown below) or use appropriate configuration entry for
creation of database table at runtime.
// This source is provided on "AS IS" basis.
create table car
(car_name varchar(20), car_model varchar(50),
car_segment varchar(50), primary key (car_name));
|
On executing Client code, we can see logs are getting written
onto the sample.txt log file, as shown follows:
2009-01-04 09:01:11,578 [main] CaptureSQL - Loging SQL statement .start
2009-01-04 09:01:11,593 [main] CaptureSQL -
This is a log statement before onPrepareStatement:
<<The DML used in this operation on the Session opened with
CatureSQL as interceptor>>
2009-01-04 09:01:11,593 [main] CaptureSQL - Loging SQL statement .end
There are many other interesting callback methods
can be used from EmptyInterceptor, such as
findDirty -> to check where the Entity in use is dirty or not.
-> if this method returns an empty int[] array, then
the Entity object supplied in argument of this
method is not dirty.
-> if this method returns an empty int[] array, then
the Entity object is dirty or is updated by some other
process in database.
-> by returning a null from the overridden findDirty method
one can opt for using Hibernate's own or default dirty
checking mechanism.
onLoad -> it is called just before Entity object is initialized.
onDelete -> it is called just before Entity object is deleted.
and many more callback methods as defined in
org.hibernate.Intercept interface.
Hibernate Question on Interceptor 2:
Can there be any Interceptor for SessionFactory, so that
it can be used across all the Session from this SessionFactory?
Yes, there can be an Interceptor defined in
org.hibernate.cfg.Configuration
to be defined during SessionFactory creation.
Configuration.setInterceptor method can be used for this purpose.
Hibernate Question on Interceptor 3:
Can one be able to use Hibernate Session from within the callback
methods of Interceptor?
No, Session may not be used from the callback methods of Interceptor.
Hibernate Question on Interceptor 4:
Can the collection be recreated/initialized lazily while executing any
callback method from Interceptor?
No, Collection may not be lazily initialized, from callback method
of Interceptors.
Interceptors in Hibernate Framework can be of two different scopes,
such as session scoped and session factory scoped.
In this example and above code is implemented using Hibernate sesssion
scoped interceptors in mind.
In the following section we shall re-create this example using
Hibernate session factory scoped interceptor.
Just you have to do is to change the static initializer block in the Client
program, and set appropriate interceptor instance into the Configuration
instance, and use this interceptor while building Hibernate session factory.
And of course you may open session with no interceptor instance passed as
constructor argument in the createRecord method.
Code snippet as shown below:
// This source is provided on "AS IS" basis.
static {
try {
// Create the SessionFactory from hibernate.cfg.xml
sessionFactory = new Configuration().setInterceptor(new CaptureSQL()).configure().buildSessionFactory();
} catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}
|
If you like to share your comment/suggestions/feedback relating to this Page,
you can do so by droping us an email at
usingframeworks @ gmail . com
with the subject line mentioning URL for this Page (i.e,
/Hibernate-Interceptor-example.php) or use this
LINK.
As per this website's privacy policy, we never disclose your email id,
though we shall post your comments/suggestions/feedback with
your name (optional) and date on this Page. If you don't want your
comments/suggestions/feedback to be shared in this Page, please
mention so in your email to us. Thank you very much.....
If anything missed out , please let me know at
techienjoy at yahoo . com
