JDBC stands for Java Database Connectivity. It provides a set of Java API for accessing the relational databases from Java program. These Java APIs enables Java programs to execute SQL statements and interact with any SQL compliant database.
JDBC provides a flexible architecture to write a database independent application that can run on different platforms and interact with different DBMS without any modification.

Pros and Cons of JDBC

Pros of JDBC

Cons of JDBC

Clean and simple SQL processing

Good performance with large data

Very good for small applications

Simple syntax so easy to learn

Complex if it is used in large projects

Large programming overhead

No encapsulation

Hard to implement MVC concept

Query is DBMS specific

Why Object Relational Mapping (ORM)?

When we work with an object-oriented system, there is a mismatch between the object model and the relational database. RDBMSs represent data in a tabular format whereas object-oriented languages, such as Java or C# represent it as an interconnected graph of objects.
Consider the following Java Class with proper constructors and associated public function −

public class Employee {
private int id;
private String first_name; 
private String last_name; 
private int salary;

public Employee() {}
public Employee(String fname, String lname, int salary) {
this.first_name = fname;
this.last_name = lname;
this.salary = salary;
}

public int getId() {
return id;
}

public String getFirstName() {
return first_name;
}

public String getLastName() {
return last_name;
}

public int getSalary() {
return salary;
}
}

Consider the above objects are to be stored and retrieved into the following RDBMS table −

create table EMPLOYEE (
id INT NOT NULL auto_increment,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary INT default NULL,
PRIMARY KEY (id)
);

First problem, what if we need to modify the design of our database after having developed a few pages or our application? Second, loading and storing objects in a relational database exposes us to the following five mismatch problems −

Sr.No.	Mismatch & Description
1	Granularity Sometimes you will have an object model, which has more classes than the number of corresponding tables in the database.
2	Inheritance RDBMSs do not define anything similar to Inheritance, which is a natural paradigm in object-oriented programming languages.
3	Identity An RDBMS defines exactly one notion of ‘sameness’: the primary key. Java, however, defines both object identity (a==b) and object equality (a.equals(b)).
4	Associations Object-oriented languages represent associations using object references whereas an RDBMS represents an association as a foreign key column.
5	Navigation The ways you access objects in Java and in RDBMS are fundamentally different.

The Object-Relational Mapping (ORM) is the solution to handle all the above impedance mismatches.

What is ORM?

ORM stands for Object-Relational Mapping (ORM) is a programming technique for converting data between relational databases and object oriented programming languages such as Java, C#, etc.
An ORM system has the following advantages over plain JDBC −

Sr.No.	Advantages
1	Let’s business code access objects rather than DB tables.
2	Hides details of SQL queries from OO logic.
3	Based on JDBC ‘under the hood.’
4	No need to deal with the database implementation.
5	Entities based on business concepts rather than database structure.
6	Transaction management and automatic key generation.
7	Fast development of application.

An ORM solution consists of the following four entities −

Sr.No.	Solutions
1	An API to perform basic CRUD operations on objects of persistent classes.
2	A language or API to specify queries that refer to classes and properties of classes.
3	A configurable facility for specifying mapping metadata.
4	A technique to interact with transactional objects to perform dirty checking, lazy association fetching, and other optimization functions.

Java ORM Frameworks

There are several persistent frameworks and ORM options in Java. A persistent framework is an ORM service that stores and retrieves objects into a relational database.
• Enterprise JavaBeans Entity Beans
• Java Data Objects
• Castor
• TopLink
• Spring DAO
• Hibernate
• And many more

Hibernate – Overview

Hibernate is an Object-Relational Mapping (ORM) solution for JAVA. It is an open source persistent framework created by Gavin King in 2001. It is a powerful, high performance Object-Relational Persistence and Query service for any Java Application.
Hibernate maps Java classes to database tables and from Java data types to SQL data types and relieves the developer from 95% of common data persistence related programming tasks.
Hibernate sits between traditional Java objects and database server to handle all the works in persisting those objects based on the appropriate O/R mechanisms and patterns.

hi 12

Hibernate Advantages

• Hibernate takes care of mapping Java classes to database tables using XML files and without writing any line of code.
• Provides simple APIs for storing and retrieving Java objects directly to and from the database.
• If there is change in the database or in any table, then you need to change the XML file properties only.
• Abstracts away the unfamiliar SQL types and provides a way to work around familiar Java Objects.
• Hibernate does not require an application server to operate.
• Manipulates Complex associations of objects of your database.
• Minimizes database access with smart fetching strategies.
• Provides simple querying of data.

Supported Databases

Hibernate supports almost all the major RDBMS. Following is a list of few of the database engines supported by Hibernate −
• HSQL Database Engine
• DB2/NT
• MySQL
• PostgreSQL
• FrontBase
• Oracle
• Microsoft SQL Server Database
• Sybase SQL Server
• Informix Dynamic Server

Supported Technologies

Hibernate supports a variety of other technologies, including −
• XDoclet Spring
• J2EE
• Eclipse plug-ins
• Maven

Hibernate – Architecture

Hibernate has a layered architecture which helps the user to operate without having to know the underlying APIs. Hibernate makes use of the database and configuration data to provide persistence services (and persistent objects) to the application.
Following is a very high level view of the Hibernate Application Architecture.

hi 13 1

Following is a detailed view of the Hibernate Application Architecture with its important core classes.

hi 14

Hibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java Naming and Directory Interface (JNDI). JDBC provides a rudimentary level of abstraction of functionality common to relational databases, allowing almost any database with a JDBC driver to be supported by Hibernate. JNDI and JTA allow Hibernate to be integrated with J2EE application servers.
Following section gives brief description of each of the class objects involved in Hibernate Application Architecture.

Configuration Object

The Configuration object is the first Hibernate object you create in any Hibernate application. It is usually created only once during application initialization. It represents a configuration or properties file required by the Hibernate.
The Configuration object provides two keys components −
• Database Connection − This is handled through one or more configuration files supported by Hibernate. These files are hibernate.properties and hibernate.cfg.xml.
• Class Mapping Setup − This component creates the connection between the Java classes and database tables.

SessionFactory Object

Configuration object is used to create a SessionFactory object which in turn configures Hibernate for the application using the supplied configuration file and allows for a Session object to be instantiated. The SessionFactory is a thread safe object and used by all the threads of an application.
The SessionFactory is a heavyweight object; it is usually created during application start up and kept for later use. You would need one SessionFactory object per database using a separate configuration file. So, if you are using multiple databases, then you would have to create multiple SessionFactory objects.

Session Object

A Session is used to get a physical connection with a database. The Session object is lightweight and designed to be instantiated each time an interaction is needed with the database. Persistent objects are saved and retrieved through a Session object.
The session objects should not be kept open for a long time because they are not usually thread safe and they should be created and destroyed them as needed.

Transaction Object

A Transaction represents a unit of work with the database and most of the RDBMS supports transaction functionality. Transactions in Hibernate are handled by an underlying transaction manager and transaction (from JDBC or JTA).
This is an optional object and Hibernate applications may choose not to use this interface, instead managing transactions in their own application code.

Query Object

Query objects use SQL or Hibernate Query Language (HQL) string to retrieve data from the database and create objects. A Query instance is used to bind query parameters, limit the number of results returned by the query, and finally to execute the query.

Criteria Object

Criteria objects are used to create and execute object oriented criteria queries to retrieve objects.

So, this brings us to the end of blog. This Tecklearn ‘ORM Overview and Overview of Hibernate’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Hibernate and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

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Java and JEE Certification Training is designed by professionals as per the industrial requirements and demands. This training encompasses comprehensive knowledge on basic and advanced concepts of core Java & J2EE along with popular frameworks like Hibernate, Spring & SOA. In this course, you will gain expertise in concepts like Java Array, Java OOPs, Java Function, Java Loops, Java Collections, Java Thread, Java Servlet, and Web Services using industry use-cases and this will help you to become a certified Java expert.

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What you will Learn in this Course?

Introduction to Java

• Java Fundamentals
• Introduction to Java Basics
• Features of Java
• Various components of Java language
• Benefits of Java over other programming languages
• Key Benefits of Java

Installation and IDE’s for Java Programming Language

• Installation of Java
• Setting up of Eclipse IDE
• Components of Java Program
• Editors and IDEs used for Java Programming
• Writing a Simple Java Program

Data Handling and Functions

• Data types, Operations, Compilation process, Class files, Loops, Conditions
• Using Loop Constructs
• Arrays- Single Dimensional and Multi-Dimensional
• Functions
• Functions with Arguments

OOPS in Java: Concept of Object Orientation

• Object Oriented Programming in Java
• Implement classes and objects in Java
• Create Class Constructors
• Overload Constructors
• Inheritance
• Inherit Classes and create sub-classes
• Implement abstract classes and methods
• Use static keyword
• Implement Interfaces and use it

Polymorphism, Packages and String Handling

• Concept of Static and Run time Polymorphism
• Function Overloading
• String Handling –String Class
• Java Packages

Exception Handling and Multi-Threading

• Exception handling
• Various Types of Exception Handling
• Introduction to multi-threading in Java
• Extending the thread class
• Synchronizing the thread

File Handling in Java

• Input Output Streams
• Java.io Package
• File Handling in Java

Java Collections

• Wrapper Classes and Inner Classes: Integer, Character, Boolean, Float etc
• Applet Programs: How to write UI programs with Applet, Java.lang, Java.io, Java.util
• Collections: ArrayList, Vector, HashSet, TreeSet, HashMap, HashTable

Java Database Connectivity (JDBC)

• Introduction to SQL: Connect, Insert, Update, Delete, Select
• Introduction to JDBC and Architecture of JDBC
• Insert/Update/Delete/Select Operations using JDBC
• Batch Processing Transaction
• Management: Commit and Rollback

Java Enterprise Edition – Servlets

• Introduction to J2EE
• Client Server architecture
• URL, Port Number, Request, Response
• Need for servlets
• Servlet fundamentals
• Setting up a web project in Eclipse
• Configuring and running the web app with servlets
• GET and POST request in web application with demo
• Servlet lifecycle
• Servlets Continued
• Session tracking and filter
• Forward and include Servlet request dispatchers

Java Server Pages (JSP)

• Fundamentals of Java Server Page
• Writing a code using JSP
• The architecture of JSP
• JSP Continued
• JSP elements: Scriptlets, expressions, declaration
• JSP standard actions
• JSP directives
• Introduction to JavaBeans
• ServletConfig and ServletContext
• Servlet Chaining
• Cookies Management
• Session Management

Hibernate

• Introduction to Hibernate
• Introduction to ORM
• ORM features
• Hibernate as an ORM framework
• Hibernate features
• Setting up a project with Hibernate framework
• Basic APIs needed to do CRUD operations with Hibernate
• Hibernate Architecture

POJO (Plain Old Java Object)

• POJO (Plain Old Java Object)
• Persistent Objects
• Lifecycle of Persistent Object

Spring

• Introduction to Spring
• Spring Fundamentals
• Advanced Spring

Got a question for us? Please mention it in the comments section and we will get back to you.

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