Several times i have to search for the compiled JSP in different Application server. So i have create this list of location.

What is a servletcontext

ServletContext is a configuration Object which is created when web application is started. It contains different initialization parameter that can be configured in web.xml.

Example of ServletContext with scenario

You are developing a web application where you want to access the email of administrator in whole application. You want to set this email id @ one location and every Servlet and Jsp can access that email. In that case you will take the help of ServletContext. You can add this email in servletcontext via init parameter in web.xml. Now this value (Email id of administrator) will be available to every Jsp and Servlet in the web application.

Life Cycle of ServletContext

Step 1: Servlet container reads the DD (Deployment Descriptor – web.xml) and creates the name/value string pair for each <context-param> when web application is getting started.

Step 2: Container creates the new Instance of ServletContext.

Note*: ServletContext is an Interface.

Step 3: Servlet container gives the ServletContext a reference to each name/value pair of the context init parameter.

Step 4: Every servlet and JSP in the same web application will now has access to this ServletContext.

Servlet context init parameter Syntax

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">

  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>
</web-app>

Difference from ServletConfig

• ServletConfig is one per servlet while ServletContext is one per web application.
• ServletContext is available to all servlet & jsp in web application while ServletConfig will be available only specific servlet.
• Difference in the syntax for servletcontext and servletconfig.

What is servletcontextlistener

Now you know that you can set init parameter in ServletContext & this Servletcontext will be initialized when application starts. After initialization this servletcontext will be available to all servlet and jsp. But what if you want to perform some kind of action when context initialization/destruction process happens. This is the situation when you will take the help of servletcontextlistener.

Bullet Points

• Only one ServletContext is available per web application.
• Every servlet in the same web application will have access to servletcontext.
• It is used to access application level parameter.
• If application is in distributed environment then there will be one servletcontext per JVM.
• ServletContext has init parameter that can be configured in web.xml.

What is Servlet Container

Normal Java application’s starting point is Main(public static void main(String args[])) method. When ever java application needs to start, main method of the application should be invoked. But in case of Servlet this is not true, Servlet doesn’t contain any main method. So who will initiate and run the method of Servlet. It’s Container who has the full control of Servlets. Tomcat is the example of Servlet container.

How it works

When ever user request for any resource from Server Web server(Apache) will pass the request to Servlet Container(Tomcat) instead of directly to servlet. It is container who will create request and response Object and then pass it to Servlet eligible for asked resource and invoke service method of Servlet.

Services Provided by Container

• Communication Support
• Servlet Life cycle management
• MultiThreading Support
• JSP Support

Different Actors in Web application

There are different actors which comes into picture of web application.

• End User
• Web Client(Browser Application)
• Server(Web Server / Application Server)
• Actual Page requested on Server

User : It’s the end user who actually raise the request for a page on Server or submit a form.

Web Client : Browsers(IE, Firefox..) are software that knows how to communicate with servers using HTTP protocol and render the page recieved from server in the form of HTML.

Server : Servers are kind of software which handle the user request and search for the content requested by end User and return the appropriate result(Requested Page or Error Code). Server can be of two type web server and App Server. It’s web server which directly handles the user request and pass it to app server to process.

What is HTML

HTML(Hyper text markup Language) is a language used by servers to send the response to Browser’s so that they(Browsers) can render the page properly on user side.

What is HTTP Protocol

HTTP(Hyper Text Transfer Protocol) is protocol used by client(Browser) and server(Web Server) to communicate.  HTTP has web specific featured that  runs on TCP/IP protocol. Structure of HTTP conversation can be divided in two types, HTTP Request or HTTP Response.

Note*: HTML can be the part of HTTP protocol response.

HTTP Request

When ever end User clicks any link or submit any form browser send HTTP Request to Server so that server can process it and provide the HTTP Response.

HTTP Request’s are of different kind. HTTP has several methods which inform the server about the kind of Request is being made by browser.

Methods in HTTP Protocol

• GET
• POST
• PUT
• DELETE
• HEAD
• TRACE
• OPTION
• CONNECT

GET method is the default method which will be used by Browser(If not specified explicitly). GET method is used by browser to ask(Not submitting any data) for some kind of resources on server(HTML, Image, PDF  etc..).

POST method is used by browser to send some information to server for processing. Eg.  Form Submission..

HTTP Request Example

Host            =javabeginnerstutorial.com
User-Agent      =Mozilla/5.0 (Windows NT 6.0; rv:15.0) Gecko/20100101 Firefox/15.0.1
Accept          =text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language =en-gb,en;q=0.5
Accept-Encoding =gzip, deflate
Connection      =keep-alive
Cookie          =****Deleted Date *********
If-None-Match   =****Deleted Date *********

Difference between GET and POST method

GET method used for asking some data from server. While POST is used for submission some data to server.

GET is idempotent while POST is not idempotent.

GET do not have any BODY part while POST has.

GET can submit some data but that will be the part of Header  and there is limitation on data submitted via GET method while Post can submit data in body part and there is no restriction on data that can be submitted in POST request.

HTTP Response

This is what server send to user client(Browser) when user ask for something from Server(GET / POST Request). HTTP Response contains Header and a Body part.

HTTP Response Header Contains below information along with others

• Protocol Version(Used by web server)
• HTTP Status Code(Successful/Fail/Not Found….)
• Content Type (MIME Type)
• Content Length
• Date
• Server details

Content Type(content-type) in header part of HTTP response is also known as MIME type. This information is used to tell the browser the kind of data server is sending,  weather it is Image or Text or PDF or anything else. According to this information Browser will know how to handle the data.

HTTP Response, Body part contains the HTML or other content that needs to be rendered by Browser on client side.

HTTP Response Example

Status           =OK - 200
Date             =Sun, 07 Oct 2012 18:00:32 GMT
Server           =Apache
X-Pingback       =http://javabeginnerstutorial.com/
Vary             =Accept-Encoding,Cookie,User-Agent
Expires          =Sun, 07 Oct 2012 19:00:33 GMT
Pragma           =public
Cache-Control    =max-age=3600, public, must-revalidate, proxy-revalidate
Etag             =89aba25474c721198ed96b924c270932
X-Powered-By     =W3 Total Cache/0.9.2.4
Content-Encoding =gzip
Set-Cookie       =PHPSESSID=3ccad49ae7e632de2f908b8ba36e70a5; path=/
Last-Modified    =Sun, 07 Oct 2012 18:00:33 GMT
Content-Type     =text/html; charset=UTF-8
X-Cache          =*****************Deleted Data***************
X-Cache-Lookup   =*****************Deleted Data***************
Via              =*****************Deleted Data***************
Connection       =close

Objective :

• How to get the MAC Address of a computer?
• How to get the MAC Address of a computer using Java?
• How to get the MAC Address of a computer via programming?

Today we’ll look into a rare feature of Java: variable shadowing

First, let’s define what is a shadowed field or method:

A field is considered shadowed when

• a subclass of its declaring class declares a field with the same name and same
• a variable having the same name and type is declared in the local scope
• a method argument/parameter is declared with a same name and type

Servlet Basic

Advantage of Using Container

Servlet Life Cycle

ServletConfig

ServletContext

JSP Basic

JSP Elements

There are 4 basic JSP elements.

• Scriptlet
• Directive
• Expression
• Declaration

Scriptlet

<%
system.out.println("Hello");
%>

Directive

Type of Directive

Its a way to give instruction to Container on at page translation time. Type of Directive

• page
• include
• taglib

Page Directive

Syntax

<%@ %>

Single package import

<%@ page import="java.lang.*" %>

Multiple package Import

<%@ page import="java.lang.*,java.lang.util.*" %>

Expression

Syntax

<%= contact.getName()%>

<%= x %>

<%= this.x %>

Declaration

Syntax

<%! int i=0;%>

<%! String getName()
{
   String name = "JBT";
    return name;
}
%>

Implicit Object

There are some implicit object which container will provide to use directly in JSP these are called Implicit Object. There are 9 implicit Object in JSP

• out
• request
• response
• session
• application
• config
• exception
• pageContext
• page

These implicit objects are map to Object from Servlet/JSP API.

JSP Comment

HTML Comment

<!-- Comment -->

JSP Comment

<%-- Comment --%>