IT-Kids

Chapter 02: Installing a Database Server

2011-03-02T19:19:00.007+05:30

1) Installing MySQL

MySQL is an open-source RDBMS. We will install this to learn SQL.

Installing MySQL is very easy. Follow these steps.

1) Just search in Google for Download MySQL

2) Download the software named MySQL Community Server

3) Choose the hardware architecture. x86 or x64. (It is x86 most of the time for Home PC's)

Once the installer is downloaded, watch the below video for installation instructions.

2) Installing Oracle XE

Oracle XE is a free version of Database released by Oracle. We will install this also. It will help you understand that all the databases are SAME, and speak the language SQL.

Installing Oracle XE is also very easy. Follow these steps.

1) Just search in Google for Download Oracle XE, and go to the downloads page.

2) Download the software named Oracle Database 10g Express Edition (OracleXEUniv.exe)

3) Choose the hardware architecture. x86 or x64. (It is x86 most of the time for Home PC's)

Download:

Click here to download Chapter-2 Video

Note:
Choose Slow Download option in the download page.
Use VLC Media Player if this file is not opening in Windows Media Player.

Chapter 01: An Introduction to Databases

2010-04-17T21:18:00.007+05:30

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What:

We all know Database is used for storing Data. There are billions of technical definitions available, but we will just continue with this simple definition for now ;-)

Why:

Once upon a time, Computing is used for only Mathematical Calculations. A need for permanent storage of data was not there then. In this new age of Computing, we need to permanently store data for future processing. Example situations are available in millions. Be it, a list of employees in a company or students in a school/university, online reservation systems and lot more. We just can't keep records in hand-written notebooks anymore.

Problem with Previous Techniques:

When we talk about Permanent storage, don't we have files ? Text documents ? Word Documents ? Excel spreadsheets ?

Open a Notepad
Type a list of 10 or 20 employees
Save it as Employees.txt

Well, yes. We did it. We permanently stored data. Why need a Database then? Answer lies behind the advancement of Computing. Consider the following situation.

I need the list of employees joined this year ?
I need the no. of employees retiring this year ?
How many employees have a P.G Degree in Mathematics ?
Which department has the most number of Employees ?

Now, doing this manually would be a herculean task.You open the employee.txt file, check and count the employees. If it is 10 or 20 employees, fine. But how about, 100 ? or 1000 ? or assume 20 Million ?

It has just become impossible. Retrieval was extremely difficult. Even managing the data would be even more difficult, in terms of adding a new record or modifying an existing one, say for example - changing phone/address of an employee. Such tasks can be achieved in Micro Seconds if you are using a Database. That's why Computing has advanced and created a data storage TECHNOLOGY called DATABASE using which data can be stored,retrieved & maintained easily & effectively.

Well, we just got an Improved definition !

Database Model

Now that you understood Database stores data somewhere & helps you maintain it efficiently, you should also know that there are different Database Models available that define HOW THE DATA IS STORED !

Some standard models available are Relational Model, Network Model, Object-Oriented model...

You should remember that in all those models, the Data is still stored in a file BUT the way it is stored and retrieved is different. This is performed by something called DBMS.

DBMS

DBMS is the next buzzword used most of the times in Databases technology.

It's the abbreviation of DataBase Management System.
DBMS is a software.
It helps you create and manage a DATABASE.
It will work based on one of the Database models described above.
RDBMS is a DBMS software that implements the RELATIONAL Model.
RELATIONAL Model uses TABLES to represent data.
TABLES are a collection of rows and columns.
Below is a good example of TABLE

Emp_Id	Emp_Name	Age	DateJoined
1001	Vignesh	23	OCT-22-2008
1002	Raju	25	NOV-13-2007
1003	Sachin	35	APR-24-2006

Most of the Prominent Databases available these days are RDBMS.

Few examples are - Oracle, MySQL, MS SQL Server.

Hmmm.....Familiar names, aren't they ?

Apart from storage & retrieval, DBMS softwares provide some extraordinary features like the following.

Allows concurrency
Control security
Maintain data integrity
Provide options for backup and recovery
Control redundancy
Provide non-procedural query language
Perform automatic query optimization

Database Schema

Once you install an RDBMS, you need to create a database schema.
A database schema is a collection of Database objects.
Database objects are the various concepts/features provided by a DBMS like, Tables, Views, Indexes, Sequences, Functions, Procedures, etc.,
For Example, we can have a schema named UniversityXYZ which will contain some 15 tables, 10 views, 32 functions etc.,
So, Schema helps us GROUP the database objects together.

SQL

You have something called DATABASE which will store data. Now, to STORE and RETRIEVE, you will need a STANDARD FORMAT to communicate with the DBMS software. If you are going to store some employee details in a Database like ORACLE, how will you add a new employee ?

Two approaches.

Hi Computer, Mr.X has unfortunately joined our company TODAY. Please add this pathetic young man to your database.
INSERT INTO Employees VALUES('Mr.X', '17-APR-2010')

We are storing data of one employee in database. And the important thing here is - how you STORE it in database. First example, English sentence...the compter cannont undertstand.....That's why you have a standard language......named as SQL. The beauty is that the above Query will be accepted by any RDBMS !

Because SQL is a common standard and is understood by all the RDBMS like Oracle, MySQL etc.,

SQL is the abbreviation of Structured Query Language.
It was accepted as the STANDARD language for Databases.
SQL has a set of KEYWORDS using which you write a Query.
A Query is a request to the database to perform an operation.
There are two basic type of SQL namely, DDL & DML.
DDL - Data Definition language - used to create, delete database objects.
Some standard DDL Keywords are CREATE & DROP.
DML - Data Manipulation Language used to retrive & modify data.
Some standard DML Keywords are SELECT, INSERT, UPDATE & DELETE.

Chapter 11: J2EE – The Eclipse Way

2009-10-21T01:11:00.002+05:30

Why Tools?

Often we repeatedly do something which turns out to be time consuming and frustrating over a period of time. Not only in computing but this happens in general. Most of the times, we tend to automate it & make it easier to accomplish.
So the aim of software is to automate these type human tasks and save time, effort, money. But the funny part is that the developer who creates a software also has a set of repeated tasks. What are the possibilities ?
For example, let’s take the compilation of servlets. what are we doing there ?

We write the servlet program, save it as filename.java under the src folder.
We compile it and A filename.class gets created.
We copy (or cut) the .class file and paste it in classes folder.
Reload the application.

Now even if we make a small change, we have to repeat all 4 steps. Consider if we have some 50 servlets in the src folder, repeating them lead to horrible software development.

Code for Code

Tools are developed these days to make software development quick and easy. These tools are usually termed as IDE (Integrated Development Environment). So i tagged “Code for Code”, just because people write code to develop a tool which will be used to code :) Like “Tit for Tat”.

Advantage of Tools

Using a tool for software development makes life easy for a programmer.
Basically speaking (oops, it’s writing actually :)) tools gives,

Efficiency: Enhances coding productivity.
Speed: Lesser development time.

Technically speaking, a tool has the following common features.

Syntax highlighting for better visibility.
Validation mechanisms that helps get rid of errors during development itself.
Code Assists that provides technical insights.
Automatic compilations & builds.

What: Eclipse IDE

Eclipse is a free, open-source multi-language software development environment comprising an IDE and a plug-in system to extend it. It is written primarily in Java and can be used to develop applications in Java and, by means of the various plug-ins, in other languages as well, including C, C++, COBOL, Python, Perl, PHP, and others.

(Taken from Wikepedia)

Eclipse: Installation

Installing eclipse is equal to unzipping a .zip file. Only two steps.

Download eclipse (click here to download)
Unzip the downloaded file (to anywhere in your hard disk).

That’s it. Installation complete. Start coding. Have fun. Enjoy the pleasure of the advantages.

Tomcat Plug-in for Eclipse

Eclipse is a tool which has a limited set of features after installation. It provides a feature called plug-in using which we can add any feature later. Tomcat has provided a plug-in for eclipse using which we can start/stop the tomcat server from eclipse itself.
When we create a Tomcat project, eclipse will automatically create the standard folder structure for you. Like the WEB-INF, src, classes etc.,

Tomcat Plug-in: Installation

Again, Installing an eclipse plug-in is equal to unzipping a .zip file. Only two steps.

Download Tomcat Plug-in for eclipse (click here to download)
Unzip the downloaded file (to <eclipse-install-dir> \ plugins folder).

Watch the below video to learn more….

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Chapter 10: More Examples: JSP + Servlets

2009-09-26T15:41:00.003+05:30

What now?

Both JSP and servlets combined together forms a better web application. Lets write a sample application that involves both JSP and Servlets.
we will use four files for this example.

home.jsp
AuthenticateServlet.java
welcome.jsp
error.jsp

Examples

index.jsp

This is like our login page where the user will enter an username and password.

<HTML>
<BODY>
<h5>Welcome to VikiMail !</h5>
<h4>Login</h4>
<FORM ACTION = "AuthenticateUser" METHOD ="POST">
Username: <INPUT TYPE = "TEXT" NAME = "username"><BR>
Password: <INPUT TYPE = "PASSWORD" NAME = "password"><BR>
<INPUT TYPE = "SUBMIT" VALUE = "Login">
</FORM>
</BODY>
</HTML>

AuthenticateServlet.java

This is the only servlet program in our example. It will be invoked when we enter username/password and submit the index.jsp page.
For making it simple, this servlet just checks if the password is super*, goes to success.jsp. Otherwise it will go to error.jsp

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class AuthenticateServlet extends HttpServlet
{
public void doPost
(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
String username = request.getParameter("username").toString();
String password = request.getParameter("password").toString();
if(password.equals("super*"))
response.sendRedirect("success.jsp");
else
response.sendRedirect("error.jsp");
}
}

web.xml

This file, usually resides inside the WEB-INF folder. Whatever servlets we have written in our application, we need to specify it here.
In our case there is one servlet called AuthenticateServlet.java.

Mapping with web.xml

Follow these steps to add a servlet mapping.
1) Create a <servlet> </servlet> tag.
2) Create a <servlet-name> tag and <servlet-class> tag INSIDE the <servlet> tag like shown below.
<servlet>
<servlet-name> </servlet-name>
<servlet-class> </servlet-class>
</servlet>
3) In <servlet-class>, give the .class name of the servlet program. The name you specify here must be the same name as the servlet program file name.
4) In </servlet-name> tag, give any dummy name. This is like a reference name for mapping purposes. The dummy name given here needs be specified exactly in another place of the web.xml file.

<servlet>
<servlet-name>CallAuthenticate</servlet-name>
<servlet-class>AuthenticateServlet</servlet-class>
</servlet>
5) Create a <servlet-mapping> tag and inside that, create two other tags namely, <servlet-name> and <url-pattern> like the one which is shown below.
<servlet-mapping>
<servlet-name> </servlet-name>
<url-pattern> </url-pattern>
</servlet-mapping>
6) In the <servlet-name> tag (under <servlet-mapping>), give the same dummy name that you specified in the <servlet-name> tag under <servlet> tag.
7) Finally in the <url-pattern> tag, give this symbol first. : /
8) Followed by the slash, give any URL name.
Remember: This URL pattern will be specified in the ACTION attribute of the <form> tag in the jsp page. (Check the index.jsp page)
After changing everything, your web.xml will look something like this.
Note: Follow the same procedure for creating servlet mappings. Except for the (1)Actual java file name (2) dummy servlet name and the (3) URL Pattern, everything procedure remains same.

web.xml

<?xml version="1.0"?>
<web-app
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
<display-name>Demo Application</display-name>
<description>
For Learning purposes.
</description>
<servlet>
<servlet-name>CallAuthenticate</servlet-name>
<servlet-class>AuthenticateServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CallAuthenticate</servlet-name>
<url-pattern>/AuthenticateUser</url-pattern>
</servlet-mapping>
</web-app>

success.jsp

This is the page that the servlet re-directs to when the password is correct.

<HTML>
<h5>Welcome!</h5><BR>
<h4>Login Successful</h4>
</HTML>

error.jsp

This is the page that the servlet re-directs to when the password is wrong.

<HTML>
<h5>Sorry!</h5><BR>
<h4>Login failed</h4>
</HTML>

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Chapter 09: Beginning Servlets

2009-09-08T02:04:00.004+05:30

What: Servlet

A Servlet is a Java Program that extends HttpServlet class. A servlet is basically responsible for processing request & sending response to the client. Servlet helps developing a more robust, secure web application.

Like: Servlet

These are the other scripting languages that are like Java Servlet. If you are learning a concept, it’s good to know the counterparts.

CGI
PHP
ASP.NET

The King: web.xml

An XML file called "web.xml" contains information about all the servlets written in a java application. This is the most important file in a JEE web application and it is mandatory. Inside the project folder/directory, a folder called “WEB-INF” should be created. Inside this folder, the web.xml file needs to be placed.

Example:

<?xml version="1.0"?>
<web-app
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
<display-name>Demo Application</display-name>
<description>
For Learning purposes.
</description>
<servlet>
<servlet-name>MyFirstServlet</servlet-name>
<servlet-class>DemoServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>MyFirstServlet</servlet-name>
<url-pattern>/HitTheServlet</url-pattern>
</servlet-mapping>
</web-app>

Servlet Vs JSP

Both Servlet and JSP are basically same. A JSP is actually converted to a servlet before execution. Whenever a JSP file is executed, it is first compiled into a Java Servlet & then executed by the server.

My First Servlet

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet
{
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
PrintWriter out = response.getWriter();
out.println("Hello World");
}
}

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Chapter 08: More JSP Examples

2009-09-05T01:59:00.004+05:30

With this chapter, we will wind up jsp and start learning Servlets. Of course there are too many topics we missed out in jsp but the objective of my blog is to get you started. Once you get the start, you will learn everything on your own. From my experience, Self-Learning is the best learning.
I will discuss two more examples on jsp in this chapter.

Example 1: The Dynamic Table

We will build a multiplication table which we've come across during our early school days.
First, i will build it with HTML Alone. Then we will do it the JSP way.

table.html

The following table is a static one. It’s just a multiplication table of 5.

<html>
<h3>5 Table</h3>
<TABLE border = 1>

<TR><TH>A</TH><TH>B</TH></TR>

<tr><td>1 * 5</td><td>5</td></tr>
<tr><td>2 * 5</td><td>10</td></tr>
<tr><td>3 * 5</td><td>15</td></tr>
<tr><td>4 * 5</td><td>20</td></tr>
<tr><td>5 * 5</td><td>25</td></tr>

<TABLE>

</html>

table.jsp

Here we go…Our cute dynamic one. Notice the number of Multiply operation performed in both the examples. It’s 5 lines in the HTML version. But here, it’s just ONLY ONE line. The number you define in the for loop, decides the number of rows. Check out the video @ the end of this blog to see this in action.

<html>

<h3>5 Tables</h3>

<TABLE border = 1>
<TR><TH>A</TH><TH>B</TH></TR>

<%
int number = 5;
for(int i = 1; i <= number ; i++)
{
%>
<tr><td>1 * <%=number%></td><td><%=number*i%></td></tr>
<%
}
%>

<TABLE>

</html>

Example 2: Website Helper

where1.jsp

This is a typical “Re-direct” example. If you just say the name of the site, it takes you right there. This where1.jsp has the HTML form where you give the input.

<HTML>
<h3>Where do you want to go ?</h3>
Enter the site name alone. Dont give www, http.
<BR>Eg., Yahoo.

<FORM ACTION = "where2.jsp" METHOD = "POST">
<BR><B>Website : <INPUT TYPE = TEXT NAME = "website">
<BR><INPUT TYPE = SUBMIT VALUE = "Go !">
</FORM>
</HTML>

where2.jsp

Once you define a site, the following piece of code will attach http, www, com to the name and performs a re-direct.

<HTML>
<%
String siteName = request.getParameter("website");
String siteURL = "http://www."+ siteName + ".com";
response.sendRedirect(siteURL);
%>
</HTML>

What Next?

Well, there is a lot, lot & lot to learn. It will never end and you should never stop learning. What i have taught you in 8 chapters is just a start. You need to keep surfing more & explore JSP. We will now move to servlets.

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Video: Part 1

Video: Part 2

Chapter 07: Working with Forms

2009-08-28T00:08:00.003+05:30

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Why Forms ?

Forms are the foremost feature found in any web application. I refer form to the HTML "Form" Tag. We do know that we can add Text Box, Buttons, List box to the web page using this Form tag.
So to interact with the user, using forms is inevitable. Let's go and see some examples around the web & figure out how important Forms are....

Examples

Yahoo! Mail - Registration Page
This site is world famous & most of us have created an account in Yahoo!
This registration page is built using HTML "Forms" Tag only.
Google - Advanced Search Window
Yet another example of a form...See, if you want to get data from the user, you need a form. Just imagine how it is processed. Let's imagine the steps that follows...

You will fill the form.
Then submit the form.
Then Google server will catch all your inputs.
It will completely 'change' it's way of search.
When you search again, you get different results.

This is indeed a terrific example of a web application. Based on user input in the form, What you see after that completely changes. Ok...Let's stop our crap stories...we had enough...Now let's go to our favorite...programming....

HTML Forms

Let’s start with a sample login form. We will have a username & password text box.
And finally, we will also add one login button at the bottom of the page.
Here is how the code will look like. Name it, “one.jsp”.

<HTML>
<FORM ACTION = "two.jsp" METHOD = "POST">
<BR><B>Username : <INPUT TYPE = TEXT NAME = "username">
<BR><B>Password : <INPUT TYPE = TEXT NAME = "password">
<BR><INPUT TYPE = SUBMIT VALUE = "LOGIN">
</FORM>
</HTML>

HTML Forms & JSP
Now let’s find out what JSP has to do with this. Listen, you designed a page. You got text boxes to type. Think what next. Well, the answer is processing. Once you have your data, you need to process. For example, say once you click on the login button, you have to search the database and validate the login. Whether the user actually has an account & given the right password. Too much theory ? Don’t worry.

HTML can only design the form. It is not having any feature to process data. But JSP can…

JSP uses the request attribute to get the form data. So let’s see how actually JSP does it with an example.
The following file is two.jsp

<HTML>
<h3>Form submitted successfully. </h3>
User name : <%=request.getParameter("username").toString()%>
<BR>Password : <%=request.getParameter("password").toString()%>
</HTML>

response Object

Just like the request, we have another object called response. It’s evident from the name that it contains details regarding a page response. One of the famous example used is sendRedirect. This method is used to navigate from one page to another page. Below example will check if the password entered in page one is ‘jothika’.
If yes, then it goes to success.jsp. Otherwise, it will go to failed.jsp. Try it…See it for yourselves.

<HTML>
<h3>Form submitted successfully. </h3>
User name : <%=request.getParameter("username").toString()%>
<BR>Password : <%=request.getParameter("password").toString()%>
<%
String username = request.getParameter("username").toString();
String password = request.getParameter("password").toString();
if(password.equals("jothika"))
response.sendRedirect("success.jsp");
else
response.sendRedirect("failed.jsp");
%>
</HTML>

Chapter 06: Digging JSP

2009-08-24T23:50:00.002+05:30

We discussed some basics of JSP in previous chapter. Let’s try and get along more with JSP :)

Focus for the chapter would be:

Scriptlets
out Object
request Object

1.Scriptlets

We have already seen how to embed Java expressions in JSP pages by putting them between the <%= and %> character sequences. But it is difficult to do much programming just by putting Java expressions inside HTML.

JSP also allows you to write blocks of Java code inside the JSP. You do this by placing your Java code between <% and %> characters (just like expressions, but without the = sign at the start of the sequence.)

This block of code is known as a "scriptlet". A scriptlet contains Java code that is executed every time the JSP is invoked.

Here is a modified version of our JSP from previous section, adding in a scriptlet.

<HTML>
<BODY>

<%
System.out.println( "Evaluating date now" );
java.util.Date date = new java.util.Date();
%>
Hello! The time is now <%= date %>

</BODY>
</HTML>

If you run the above example, you will notice the output from the "System.out.println" on the server log file. It will not print on the browser.

2. out Object

By itself a scriptlet does not generate HTML. If a scriptlet wants to generate HTML, it can use a variable called "out". This variable does not need to be declared. It is already predefined for scriptlets, along with some other variables. The following example shows how the scriptlet can generate HTML output.

<HTML>
<BODY>
<%
//This scriptlet declares and initializes "date"
System.out.println( "Evaluating date now" );
java.util.Date date = new java.util.Date();
%>

Hello! The time is now
<%
out.println(date);
%>
</BODY>
</HTML>

Here, instead of using an expression, we are generating the HTML directly by printing to the "out" variable. The "out" variable is of type javax.servlet.jsp.JspWriter.

Greetings ! Example

Ok. Lets try out a more informative example. This is the scenario.

If it’s a morning, it should greet me “Good Morning. Have a nice day”.
If it’s a evening, it should greet me “Good Evening, Good day”.

Ok. Try this example & let me know if you are able to do it…

3. request Object

Another very useful pre-defined variable (or object) is "request".

It is of type javax.servlet.http.HttpServletRequest

A "request" in server-side processing refers to the transaction between a browser and the server. When someone clicks or enters a URL, the browser sends a "request" to the server for that URL, and shows the data returned. As a part of this "request", various data is available, including the file the browser wants from the server, and if the request is coming from pressing a SUBMIT button, the information the user has entered in the form fields.

The JSP "request" variable is used to obtain information from the request as sent by the browser. For instance, you can find out the name of the client's host (if available, otherwise the IP address will be returned.) Let us modify the code as shown:

<HTML>
<BODY>

<%
// This scriptlet declares and initializes "date"
System.out.println( "Evaluating date now" );
java.util.Date date = new java.util.Date();
%>

Hello! The time is now

<%
out.println( date );
out.println( "<BR>Your machine's address is " );
out.println( request.getRemoteHost());
%>

</BODY>
</HTML>

A similar variable is "response". This can be used to affect the response being sent to the browser. For instance, you can call response.sendRedirect( anotherUrl ); to send a response to the browser that it should load a different URL. This response will actualy go all the way to the browser. The browser will then send a different request, to "anotherUrl". This is a little different from some other JSP mechanisms we will come across, for including another page or forwarding the browser to another page.

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Chapter 05: Beginning JSP

2009-08-23T23:15:00.001+05:30

What is JSP ?

JSP is the abbreviation of Java Server Pages.
Simply put,

JSP = HTML + Java.

HTML is a markup language & it's features are very limited. It is still simple & superb but can only generate static content. The key concept of a web application, i.e, the Dynamic Content Generation cannot be performed by HTML. So this only happens when it gets some help. To conclude the story, here is viki’s bottom liner.

When the power of Java combined with the simply-superb HTML, the outcome is technically termed JSP.

JSP: Static content

JSP simply puts Java inside HTML pages. You can take any existing HTML page and change its extension to ".jsp" instead of ".html". Take the HTML file you used in the previous exercise. Change its extension from ".html" to ".jsp". Now load the new file, with the ".jsp" extension, in your browser.

You will see the same output, but it will take longer! But only the first time. If you reload it again, it will load normally.

What is happening behind the scenes is that your JSP is being turned into a Java file, compiled and loaded. This compilation happens only once and after the first load, the file will not take more time to load. (But everytime you change the JSP file, it will be re-compiled again.)

Of course, it is not very useful to just write HTML pages with a .jsp extension!

JSP: Dynamic content

what makes JSP useful is the ability to embed Java. Put the following text in a file with .jsp extension (let us call it hello.jsp), place it in your JSP directory, and view it in a browser.

<HTML>
<BODY>
Hello! The time is now <%= new java.util.Date() %>
</BODY>
</HTML>

Notice that each time you reload the page in the browser, it comes up with the current time.

The character sequences <%= and %> enclose Java expressions, which are evaluated at run time.

This is what makes it possible to use JSP to generate dynamic HTML pages that change in response to user actions or vary from user to user.

Watch a demo below.

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Chapter 04: Know your Server

2009-08-23T19:56:00.000+05:30

There are two things you must know if you have a server.

Where to place the files (or programs) in the server.
How to access them from a web browser.

We are gonna write a sample HTML program and try to do the above steps.
In apache Tomcat, we have to place the files in the webapps folder of tomcat's installation directory. For me, it's F:\tomcat 6.0.
So, if your application name is "demo", then create a folder called "demo" under the following directory.

F:\Tomcat 6.0\webapps\demo

View the below video for understanding more.

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Chapter 03: Before Beginning: The basic Tool sets

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You might wonder why we still didn't write a single line of code even after the 3rd chapter. I understand your thoughts. But you need some patience. We are not done yet. We need to install some softwares before we get going.

Basically we need THREE tools. Java, Server, Editor.

We need to download & install the following tools.

JDK - Java Development Kit : Download
Apache Tomcat (server) : Download
Eclipse IDE : Download

No tutorial is necessary for installing java. You are not eligible to learn JEE if you don't even know how to install java. However it's not the same case for Apache Tomcat. So lets discuss about it.

Apache Tomcat:
Apache Tomcat is a servlet container developed by the Apache Software Foundation (ASF). Tomcat implements the Java Servlet and the JavaServer Pages (JSP) specifications from Sun Microsystems, and provides a "pure Java" HTTP web server environment for Java code to run.
Tomcat should not be confused with the Apache web server, which is a C implementation of an HTTP web server; these two web servers are not bundled together. Apache Tomcat includes tools for configuration and management, but can also be configured by editing XML configuration files.

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All right. We are geared up to get our hands dirty with JEE code....

Chapter 02: Before Beginning: The basic skill sets

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We just can't jump into J2EE and start learning. There are few basics concepts or skills we need to acquire first., The following skill set are compulsory learnings before beginning J2EE.

Basic knowledge on Java programming

Good understanding of HTML

Client - Server

Working knowledge of HTTP.

Basic knowledge on XML.

However, these are optional learnings but important for JEE mastery.

Java Script
CSS
Good knowledge in java

Java skills

You don't need to be a java guru to learn JEE. It's just an extra edge and absolutely not mandate. So you should have a basic understanding concepts like Class, Objects, Inheritance, Interface, Packages, Constructors, Exception Handling.

HTML skills

Again, You don't need to be a HTML guru to learn JEE. It's just an extra edge and absolutely not mandate. So you should have a basic skills on creating a sample HTML page, creating Forms, Tables, etc. If you don't have much idea, i suggest you to read the below tutorial.

http://www.w3schools.com/html/

Client - Server

Server - One who process the request. Basically server is like a java program only. It communicates with the clients who speak HTTP. I refer 'speak' to processing a request & sending back a response.HTTP is a network protocol. Client - One who raises the request. It's just YOU. When you type, "google.com" in a browser (like internet explorer) you want to open the google page. This operation is technically termed "HTTP Request". Now the GOOGLE server will accept your request, process it, returns the "google search" page. This returning operation is technically termed a "HTTP Response".

HTTP

HTTP is expanded to Hyper Text Transfer Protocol. Never care about the long confusing abbreviation. It's just a language for communication between a client & server.

If you take humans, I will order, "Tea, please".

This a request. And obviously, there comes a cup of Tea. And Voila, that's the response.

Same way, Client request is HTTP Request & Server response is HTTP Response.

But the problem is the language representation. It's not as explicit as common english.

The following passage is NOT a HTTP request.

"Dear computer Ji, i want to steal a code for my lab assignment. Please give me a working C++ program for generating the fibonacci series".

IF this is not, then what is a valid request. Interested in seeing how a valid HTTP Request will look like ?

Here you go..

The following HTTP request was received from IP address 123.236.74.4 (port 2818) by IP address 91.84.196.2 (port 80):

GET /dumprequest HTTP/1.1

Host: djce.org.uk

Connection: keep-alive

User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/530.5 (KHTML, like Gecko) Chrome/2.0.172.39 Safari/530.5

Accept:application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;

Accept-Encoding: gzip,deflate,sdch

Accept-Language: en-US,en;q=0.8

Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3

I know you cannot understand it easily. It's a computer's language & obviously it will be complicated. So to understand clearly,

XML skills

If you know what is XML and if you can create a sample XML document, Fair Enough,. You are ready to go & begin JEE learning. Or else, read the following tutorial.

http://www.w3schools.com/xml

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Chapter 01: Introduction to J2EE

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This chapter gives an overview of the what & why of J2EE. In Tamil language, i have interactively explained assuming that my best friend is sitting next to me.

J2EE is the abbreviation of Java 2 Enterprise Edition.

The jargon 'Java' can be broke up into THREE main components.

J2SE : Java 2 Standard Edition
J2EE : Java 2 Enterprise Edition.
J2ME : Java 2 Micro (or Mobile) Edition.

J2SE:

J2SE is the basic form. This is the actual programming language. The other two are actually

derivatives. It's also termed as "core java" or "pure java" in some locales. Basically used to create small scale applications that runs on a CUI. Implementation of "Applets" concept helps create GUI based applications.

Note:

CUI is Character user interface. It's like the black-white DOS prompt where you can interact with the system only via characters. GUI is Graphical user interface. As the name indicates, "Graphical", you can control the applcation through mouse & clicking buttons, etc.

J2ME:

Simply put, This edition is used for creating operating systems, softwares & games for mobiles.

J2EE:

This is what we are gonna dig in & get our hands dirty. The real deal.

Till version 1.4, it is named J2EE 1.4. Ever since 1.4, it's termed JEE these days.

Latest version, 1.5 is named JEE 5. And FYI, JEE 6 is released recently.

Normal Java (termed J2SE) is a programming language.

J2EE is Not a Programming language or a Software.

J2EE is officially termed as a "Tehnology".

For me,

JEE is

J2SE + Some API's.
Server programming language.
Used for building java - based web applications.
Supports Dynamic web page creation thorugh 'JSP' & 'Servlets' concept.

NOTE:

PHP, ASP (from Microsoft) are other counterparts for JSP. These languages are scripting languages. They are all used for building dynamic web applications.

Watch the chapter as an interactive video in tamil.

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Part 1:

Part 2:

Chapter 01: Introduction to C-Kid

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Introduction

What is this ?

There are million books for C-Language. This is not just another book. It's almost like a starter you use to have before the main course. This is a just 12 page article on C-Language. My primary objective will be promoting you to a position from where you can master C-language on your own. Getting a start is what everyone wanted & it's exactly what i am gonna give you. I will give my best to mould this mini article as simple & interesting as possible.
Happy learning !

Who are you ?

This is what i expect in you before triggering a start.

First, I assume you are a human being. lol !
Aleast Once, You might have come across the word 'computer'.
You might have took part in a C-class or course somewhere but have very little or no Knowledge about it.
You just want to learn the basics so that you can pass in the academic 'C' subject.
You need to become a world-famous programmer but didn't got the perfect start.

If you are someone different, I assume you are an expert in C-language & i welcome you to storm in with your comments & criticisms.

Lets Get Started...

A Building can be strong as a rock. Can be 10 storey's or 100 storey's. But if the basement is not built properly, then everything is gone. So before jumping in to C-language, there is something you should know. And don't worry. I am not gonna make you read boring stories. I presume.

Computer

You have seen a computer but what actually you think it is ?

This is what wikipedia says in one line.

"A computer is a machine that manipulates data according to a set of instructions".

My first impression, it's a wonderful entertainment device. I love it. From "Dave" to "GTA", i've played all the games. A Home Theatre. Music System. With my 4.1 Frontech speakers support, it has given me a wonderful movie experience. A box used to kill ample time with chatting, Facebook, orkut, Twitter,You tube and all.

This is what i think it is.

"A computer is a Total Idiot which does almost anything we order it to, anytime, any number of times."

Women likes it very much just beacuse it never asks "Why ?" and it's always at your service. I tag it an Idiot because it never thinks before doing a task. I ask you to jump in the well. Will you do it ? You will think of the after effects. But the computer never thinks about anything. It just does what you ask it to.

Life Without computer ?

At this moment, think of a life without a computer.

With hype of technology at it's peak, the fact that IT (Information Technology) enables business is blatant. I refer "business" to every possible category like banks, media, travel, automobiles, entertainment, shopping……

Simply put, everything. Now I would like to share few examples about how IT supports the business before i write brief on what i do @ work.

Here is a very simple, small scenario.

A billing system in a provisional store. Without one, the store keeper use to write down the list of items in a paper, adds them up to finally get your bill. Now the billing system not only gives the bill in a minute but also it keeps track of the total sales for the day, month & year too. Even it will order the wholesaler for more goods whenever a particular item is sold out.

My friend, Sri vallabha is a mechanical engineer by graduation. But at work he spends most of his time with a computer. You might wonder what does a mechanical engineer have to do with a computer. This is what he does.

Sri’s uses an engine automation tool using which he can ‘virtually’ build an engine & test it’s output & performance. He configures this ‘virtual’ engine with varying parameters and he gets a perfect design after finalizing the torque, size, bhp, diameter etc.,

Previously they are made physically & tested live. To get the perfect design, we need to change the parameters & manufacture the engine multiple number of times. So now you can easily understand how much time & money IT saves for his business.

Few other examples are…

The ATM you use every day
The online shopping you do with your credit card
Automation of Rocket launch.
The visual effects & sound effects in movies.

So now you have an idea of What a computer can do & it's now time we move further into technology.

Main Categories:

There are two main categories when it comes to computer.

Hardware
Software

Let's quickly find out what are these.

Hardware

Knowing this is a less priority for our goals of becoming a C-Master, but still you should be able to distinguish between hardware & software.

In my understanding, whatever part of the computer you can see, touch & feel, take a baseball bat & whack! it or lift it and throw out of the window are called Hardwares.

Dumb books use to describe it as the "Physical components of the computer". Examples are your key board, mouse, monitor, speakers and all.
Inside your CPU (Central Processing Unit) Box, there are something that is worth knowing. If you are eager to see how they look like, just click on the respective names.

MotherBoard: An electronic board which is considered the heart of the computer.
Processor: A Square-Box like device which is fit into the mother board. Intel & AMD are famous manufacturers of those.
RAM : Abbreviated to Random-Access-Memory. A small chip serves a temporay memory which is also fit into the mother board.
HDD : Hard Disk Drive or simply Hard Disk is the permanant storage device connected to the mother board through a cable (or bus, they call it technically).

Software

You might have come across this word. Definitely. Still, let me try to put it simple. Softwares are invisible components of a computer. They are logical components and there is no chances of banging! them with baseball bats.
In general, a software is a tool which is added inside a computer to perform a specific task.
Technically,
A software is a single or set of programs. A programs is a single or set of instructions.
An instruction can be any basic mathematical instruction like add or subtract or even something more complicated.
So a set of programs written to set up a Billing system is a Software as well as a small, simple, single program to add two numbers is also a software.
Simply put, it solves a purpose.

Types of Software

Don't get harsh & think that this article is getting too theoretical. I know how worse it is to read too boring theory. I've experienced it during my academics. This page has a whole lot of fundamental concepts and are Must-Know information.
So just keep reading and don't skip it like we do during exam preparations :)

Basically, there are two types of software. I will just say what they are with an example.
You know that software is a tool which is included inside a computer to perform a specific task.

Application Software

If the tool is performing a task specific to the user, then it is an application software.

Examples
Windows Media Player : Just to hear song, we use it.
Solitare Game : To kill some time, relax & enjoy, we play this famous game.
Notepad: A simple applicaion Used to compose text.
Internet Explorer: Used to browse websites.

NOTE:
Though solitare is a game, still it's actually an application software.
TIP:

Internet Explorer comes under an Application Softwares Category called "Browsers".

A Browser is an application used to communicate with the Web.

Other famous browsers are Mozilla, Firefox, Netscape, Google Chrome.

So these examples will give you a clear idea what an application software is. Bottom-line is,
The computer can perfectly function without an application software.

System Software

If the tool is performing a task specific to the system, then it is a system software.
These softwares are essential for the computer to function properly. If they aren't added to the computer, or if not working properly, then the chances are you cannot type in notepad, or hear music in Windows Media Player or open Internet Explorer.

INFO
If you think i am writing too much theory, then F.Y.I, there is a separate paper on "System Software" in Computer Science & Engineering. The book is around 800 pages. And god, please don't ask me how i passed the exam.

And even if you don't understand these below mentioned application software, don't worry. I am gonna brief them.
Examples:

Operating System : The primary, all important sofware that communicates with hardware.
Boot loader : When you press the power button of your computer, this is the first software that starts to do it's work.

Operating System: What & Why ?

As i said its "the primary, all important software", you must have a strong understanding of what an Operating System (OS) is & why is it so important to the computer.
A pretty straight simple question.

You press the "A" key in your keyboard. And an "A" exactly appears on the monitor. HOW ?
Who is doing this job ?

How the computer knows that you actually pressed "A" in the keyboard ?
Is there any genie sitting inside your CPU box & looks from a pin hole what you are hitting in the key board ?

One thing is certain. There is someone who takes this onus for this job. And now you almost found out who it is.
That someone is the "Operating System".

Ok. now you got some idea. Let's make it clear.

Assume, you have bought a brand new, high-end, costly computer at home. Everything is ready.
A 29" Monitor, 9.1 Surround speakers, 1 TB Hard disk (1024 GB) & a DVD of your all-time favourite movie.
Now, if you don't have an Operating System installed on your computer, then everything is waste.
All the million dollar worth hardwares are just like dolls.

Because whatever hardwares you have, it is the O.S, the system software that interacts with YOU & the computer hardware.
It understands your request & directs the hardwares inside the CPU box to get it done. Like a supervisor who ensures the user (it's you) requests are completed.
Here are few examples of operating systems.

Examples of O.S

Microsoft created a series of application softwares (O.S) like, Windows 98, Windows XP, Windows Vista.
Linux is a Free O.S and few of then are RedHat Linux, Mandrake Linux, Suse Linux, Ubuntu Linux.
Unix, Mac OS from Apple (manufacturer of the famous iPOD) and Solaris O.S from Sun Microsystems.

BootLoader

Huh oh....i forget to mention this one. Bootloader is another system software., Ok, so what in heaven is it doing ?
As i mentioned before, when you press the power button of your computer, this is the first software that starts.
It just loads the operating system into the computer. So without a boot loader, even an O.S is a doll ! Lol !

Ok. We're done here. We have discussed all the fundamental concepts.
Now we are gonna wind-off these stories & storm towards our goal. Programming.

Programming Languages

We saw about softwares, types, examples just now.

So a programming language is like a tool using which we can write programs.

programs means, as i said, set of instructions. IF you ask me what type of instructions ? Why instructions ?
I'm replying you. "Buy me a Cheese burger, less salt, Chicken Pizza & a schezwan fried rice. more spicy."
Anyway, you are not gonna buy me [:o] that but still you can understand what i am asking you.
Can i ask this to a computer ? will it be capable of understanding my language ?
Unfortunately, it can't. Atleast for now, 10 July, 2009, There isn't any intelligent computer built yet capable of understanding what a human being talks.

So now you know why we write programs. "Programming Language" is a 'language' which can be understood well by computers. As the computers cannot understand our language(English or Tamil or French) we are left with only one option. Learn the computers language & then talk to it. When i say 'talking', its actually not a voice but text. This text is called a program.

So, great. We're done with our first chapter. pretty small when compared to books, isn't it ?
This is what they will elaborate in 50-60 pages & which ultimately forces us fell asleep [:o]
We end chapter 01 with those 3-4 pages & i wish you are now clear with Computer, Hardware, Software, their Types, Operating system, and What + Why of Programming languages.
LINE TO REMEMBER:
You have all the privelage of asking me doubts/question/queries/suggestions, Use the 'comment' feature in case you have any !

So, what are you gonna see next ? Just get a glimpse below.
C-language is a programming language. So, it's evident. After learning C, we are gonna write programs and talk to the computer.
How about that ? Sounds cool right ? Let's do it.

Chapter 09: Finally Files.

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Chapter 08: A “Structure” Lecture.

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Chapter 07: Arrays

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Chapter 06: Breakdown with Functions

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Chapter 05: Whoop with Loops

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Chapter 04: Conditional Statements

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Chapter 03: Getting started with C

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Chapter 02: A KID story on C-language

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Network Kid

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What Is An IP Address?

IP Address (Internet Protocol Address):

This number is an exclusive number all information technology devices (printers, routers, modems, et al) use which identifies and allows them the ability to communicate with each other on a computer network. There is a standard of communication which is called an Internet Protocol standard (IP). In laymans terms it is the same as your home address. In order for you to receive snail mail at home the sending party must have your correct mailing address (IP address) in your town (network) or you do not receive bills, pizza coupons or your tax refund. The same is true for all equipment on the internet. Without this specific address, information cannot be received. IP addresses may either be assigned permanently for an Email server/Business server or a permanent home resident or temporarily, from a pool of available addresses (first come first serve) from your Internet Service Provider. A permanent number may not be available in all areas and may cost extra so be sure to ask your ISP.

Domain Name System (DNS): This allows the IP address to be translated to words. It is much easier for us to remember a word than a series of numbers. The same is true for email addresses.

For example, it is much easier for you to remember a web address name such as whatismyip.com than it is to remember 192.168.1.1 or in the case of email it is much easier to remember email@somedomain.com than email@192.168.1.1

Dynamic IP Address: An IP address that is not static and could change at any time. This IP address is issued to you from a pool of IP addresses allocated by your ISP or DHCP Server. This is for a large number of customers that do not require the same IP Address all the time for a variety of reasons. Your computer will automatically get this number as it logs on to the network and saves you the trouble of having to know details regarding the specific network configurations. This number can be assigned to anyone using a dial-up connection, Wireless and High Speed Internet connections. If you need to run your own email server or web server, it would be best to have a static IP.

Static IP Address: An IP address that is fixed and never changes. This is in contrast to a dynamic IP address which may change at any time. Most ISP's a single static IP or a block of static IP's for a few extra bucks a month.

IP version 4: Currently used by most network devices. However, with more and more computers accessing the internet, IPv4 addresses are running out quickly. Just like in a city, addresses have to be created for new neighborhoods but, if your neighborhood gets too large, you will have to come up with an entire new pool of addresses. IPv4 is limited to 4,294,967,296 addresses.

IP version 5: This is an experimental protocol for UNIX based systems. In keeping with standard UNIX (a computer Operating System) release conventions, all odd-numbered versions are considered experimental. It was never intended to be used by the general public.

IP version 6: The replacement for the aging IPv4. The estimated number of unique addresses for IPv6 is 340,282,366,920,938,463,463,374,607,431,768,211,456 or 2^128.

The old and current standard of addresses was this: 192.168.100.100 the new way can be written different ways but means the same and are all valid:

* 1080:0000:0000:0000:0000:0034:0000:417A

* 1080:0:0:0:0:34:0:417A

* 1080::34:0:417A