example code Interceptor use log SQL statements Hibernate Tutorial Example

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page is claiming to be some sort of best practices and we DO NOT expect
any of our visitor/reader of this page to assume this as some sort of
best practice for any context and should not be using this 
as it is without appropriate evaluation to their, so to say, 
specific programming context.

This page intends only to provide bit and piece of known ways  for
doing some sort of example and may not be fit for any other purpose.

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.



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 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:

 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
 

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 -
<<Your SQL used for the 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?



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No, Collection may not be lazily initialized, from callback method
of Interceptors.

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