HQL

Hibernate provides a simplified language for querying into the database. Its called HQL-Hibernate Query language.
We can use SQL Queries directly in hibernate,So naturally a question may come.Whats the need of using HQL if you can perform the same with SQL ?

1.HQL is very simple. Its very easy to learn and manipulate.
2. HQL engine generates the most appropriate SQL for a particular task from a set of SQL statements.
3.Usage of HQL will help in application portability. We can change the Database from say Oracle to MySQL without changing any HQL queries. Only change needed is in the Configuration file where we need to specify the appropriate driver and dialect.

These are some of the advantages of using HQL. I will keep you updated with more advantages soon.

Lazy Loading in Hibernate

Lazy loading is a functionality provided by Hibernate. What lazy loading does is that it doesn’t load the the associated objects for a class during startup. They will be loaded only when they are referenced. This lazy loading greatly improves the application performance. In hibernate 3.0, lazy loading is enabled by default. ie:by default the objects are only loaded as and when they are referenced. To say this in XML terms in hibernate 3.0 lazy=”true” by default for objects and lazy=”false” for collections. This default behavior of hibernate may throw in some exception called LazyInitializationException. This is a very famous exception and to whoomever you ask for an answer the default answers would be
1. setting lazy=”false” for all
2.Use session.get() instead of session.load.

I don’t think the first one can be called a solution as setting lazy=”false” is like forcing the hibernate to work without one of its most important feature.Also it degrades the performance. If the no of tables and the underlying relations are huge, then it will take a hell lot of time to perform some task. So what we can do is to
keep lazy as true and load the associated objects as and when we need it.

[Please bear with me for the time being, i will post the examples for all these once ma IDE is working fine.Till then i will continue with the theory aspect of it.]

The second one is to be used whether or not u get a Lazy Exception.I say this because method load() returns an exception in case of a null object while method get() returns a null object in the same case. So its better to use session.get() for all cases. If you are so much interested in using session.load() do it if and only if you are sure that such an object exists.

Lazy Exception can be a hard nut to crack if you don’t understand the underlying reason of it. Lazy Exception can also occur due to improper session management ie: trying to access the session after closing it.

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iText

iText is the free and open source library in Java used for generating PDF, RTF and HTML documents. It is very simple to use and manipulate. For the .NET framework there is iTextSharp similar to iText.
iText was developed by Bruno Lowagie in 1998. If you are interested in the history and what made him develop iText, Visit More on iText .
You can easily tryout the following piece of code provided you have JDK and any IDE. Download the iText.jar from and add it to the project .You can download the jar file from here.

Sample code:

/*Importing the necesary packages*/
import com.lowagie.text.Document;
import com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
import java.io.FileOutputStream;

/*Sample code for creating a new pdf document and writing into it
*@author guru_G
*/
public class SampleCode{

public static void main(String[] args) {
try{
Document pdf = new Document();
/**
*This will create a new document in the following
*path D:\ with name Document.pdf
**/
FileOutputStream file=new FileOutputStream("D:\\Document.pdf");
PdfWriter.getInstance(pdf,file);
pdf.open();
/*Adding a new paragraph in the document*/
pdf.add(new Paragraph("Manchester United"));
pdf.close();
}catch(Exception e){
System.out.println("Exception caught :"+e.getMessage());
}
}
}

Run the project and a new file will be created in D:\ with name document.pdf .

Pointers

Learn hibernate from Gavin King,Christian Bauer and team. They are the creators of hibernate. Recently i read about Gavin, he has only 5 years of experience working with Java and went on to create a framework of this magnitude.Infact knowledge of Java is not the essential thing you need to learn Hibernate.You have Nhibernate if you are a fan of .NET technologies. Gavin and Christian are presently working for the JBoss project and he is also an active member of the EJB spec. group.

Visit Hibernate home page Hibernate Core

Read the documentation .

There are also many tutorials available in the web. wait..!!! I am gonna post a tutorial in Hibernate where i will help you in each and every step of learning hibernate.

PS: I am having some problems with my Eclipse IDE. ie y the delay in posting the tutorial

An introduction to Hibernate

 

hey guys,

am gonna talk abt Hibernate..!!! its an ORM tool…

wats ORM and wats an ORM tool..?? ORM stands for Object Relational Mapping..its mapping between objects and database. we normally use JDBC to  talk 2 database from Java. Using an ORM tool like Hibernate we map java objetcs to Database. In Hibernate tables are denoted as classes and relationships are denoted by objects. there are a few terms we need to understand when we are using Hibernate.

POJO Classes- Plain Old Java Objects

These are java equivalent of the database tables, the columns in the tables are represented as member variables of the particular class with access specifer Private..all these member variables willl have getter and setter methods. The class also consists of a default constructor .We normaly add two parametrised constructors. one consisting of all the members in the class another consisting of member variables which are mandatory(ie: columns which are NOT-NULL in table).

HBM- Hibernate Mapping File

this is an xml file defining the table structure.

 

Hey all, I am gonna talk abt Hibernate..!!! Its a java persistence frame work. In simple words its  an ORM tool.

Whats ORM and whats an ORM tool..?? ORM stands for Object Relational Mapping..its mapping between objects and database. we normally use JDBC to  talk 2 database from Java. Using an ORM tool like Hibernate we map java objetcs to Database. In Hibernate tables are denoted as classes and relationships are denoted by objects. there are a few terms we need to understand when we are using Hibernate.

• POJO Classes- Plain Old Java Objects

These are java equivalent of the database tables, the columns in the tables are represented as member variables of the particular class with access specifer Private..all these member variables willl have getter and setter methods. The class also consists of a default constructor .We normaly add two parametrised constructors. one consisting of all the members in the class another consisting of member variables which are mandatory(ie: columns which are NOT-NULL in table).

• HBM- Hibernate Mapping File

An xml file defining the table structure.using the various tags available, we can define the entire schema.

• Hibernate CFG -configuration file 

Using the Configuration file we can specify the dilaect, the schema to which we need to connect, the driver to be used, the connection pool size etc etc.

Welcome

Welcome you all !! Just as the tag line says this is a 100% technical blog.
you can catch me up with more non-technical stuff here.
Happy reading…