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• Developers don't write SQL expressions into code. This saves time and increases maintainability.
• It is database independent. DBMS can be changed without changing the code. Only configuration XML is modified for this.
• It supports transaction methods and auto-creation of tables, constraints, relations (1-N,1-1, N-N, etc.).

Installation:

Requires two steps:

1. Copying required JARs into /lib directory:
2. Creating and configuring persistence.xml configuration file.

Required JARs are: 

Hibernate installation JARs

Hibernate requires only hibernate3.jar. But hibernate-jpa jar is also used generally for additional JPA properties. A database connector jar is also reqiured for connection handling. mysql-connector jar is used here for this reason. Other jars are required because of dependencies. These jars can be found on most Java developer download site with exact version numberings.

persistence.xml file is also required to map application into database. Database configuration is done in this file. It is put into /src/main/config/META-INF folder as default. Content should be as below:

Hibernate persistence.xml configuration

• persistence-unit name: Defines the configuration id. More than one persistence unit can be defined at once.
• hibernate.connection.driver_class & hibernate.dialect: Defines the database type. MySQL is used in this example.
• hibernate.connection.username & hibernate.connection.password: Defines database connection parameters.
• hibernate.connection.url: Defines database server name, port and schema. "test" is used here for schema name.

These two steps are required and enough for starting Hibernate usage. Hibernate entity definition and API usage will be explained in upcoming posts.

Spring 3 DI (dependency injection) functionality which placed in "Spring Core" is very important for managing objects (or "beans") in enterprise applications.


Here is a quick reference for bean configuration of Spring DI:

Spring Bean Configurations

Introduction
Velocity is a template engine. Using Java classes, you can inject objects into template engine and use those injected objects in velocity template (.vm) files.

•  It can be used in desktop applications, web applications and other areas where a structured text or code is required.
• It can be used as a powerful code generator. Dynamic codes are created by velocity injected objects.
• It can access all public attribute and methods of given object.
•  It has an easy and clear syntax.
• You can define user interfaces (HTML, JSP etc.) dynamically and developers and designers can work seperately. So, MVC pattern can be used too.

Here is an example velocity template file helloWorld.vm:

Hello $param

And below is an example Java file HelloWorld.java that uses the template:

import org.apache.velocity.app.VelocityEngine;

import org.apache.velocity.Template;

import org.apache.velocity.VelocityContext;

import java.io.StringWriter;

public class HelloWorld

{

    public static void main( String[] args ) throws Exception

    {

        /*  first, get and initialize an engine  */

        VelocityEngine engine = new VelocityEngine();

        engine.init();

        Template template = engine.getTemplate( "helloWorld.vm" );

        VelocityContext context = new VelocityContext();

        context.put("param", "World");

        StringWriter writer = new StringWriter();

        template.merge( context, writer );

        System.out.println( writer.toString() );    

    }

}

Console Result: Hello World

In the code Velocity engine is created, initialized, velocity tamplate file template is taken, required parameters are put into context, and at last the string is written to the screen.

Commands

Velocity also has a built-in VTL (Velocity Template Language) syntax that has following statements:

VTL Tags

Escape Tool

Because of the VTL is a template language, string operations are required widely. For that case, some escaping methods are supported for java, javascript, html, xml, sql and some character renderings exist: 

(For more detail http://velocity.apache.org/tools/devel/generic/EscapeTool.html)

For example,
$val = “Stop!”
$esc.java($java) 
produces \”Stop!\”
or
${esc.d} produces $ output.
${esc.h} produces # output.

• Free (and most of them are open source), 
• Standalone (not installed as plug-in or add-in), 
• Easy to download and install,
• No-need to registration and activation keys,
• Fast to start and use.