Web Development

The J2EE platform consists of a set of services, APIs, and protocols that provide the functionality for developing multitiered, Web-based applications.

J2EE Architectures

Excerpt from Book

Sir's class slides

J2EE Features

Java™ Database Connectivity (JDBC™) API [ Next topic ]

The standard way to connect to a database from a J2EE application or module is through a JDBC driver.

Transaction Service

The purpose of a transaction is to ensure that data is updated in an all-or-nothing fashion in order to preserve data integrity.

The transaction service provides transactional resource managers for the JDBC API, the JMS API, and resource adapters (connector modules)

Java Naming and Directory Interface™ (JNDI) API

The JNDI API allows application components and clients to look up distributed resources, services, and EJB™ components. The J2EE resources described in this guide are made available through the JNDI API

Java™ Message Service (JMS) API

The JMS API provides a common way for J2EE applications and modules to create, send, receive, and read messages in a distributed environment.

JavaMail™ API

The JavaMail API allows J2EE applications to create, send, receive, and read mail messages. The JavaMail API includes support for the IMAP4, POP3, and SMTP mail protocols. JavaMail sessions are made available through the JNDI API.

Web Server Vs Application Server, what's the difference ?

Web Server

Web server contains only web or servlet container. It can be used for servlet, jsp, struts, jsf etc. It can't be used for EJB.

It is a computer where the web content can be stored. In general web server can be used to host the web sites but there also used some other web servers also such as FTP, email, storage, gaming etc.

Examples of Web Servers are: Apache Tomcat and Resin.

It can respond to the client request in either of the following two possible ways:

Generating response by using the script and communicating with database.

Sending file to the client associated with the requested URL.

The block diagram representation of Web Server is shown below:

Important points

If the requested web page at the client side is not found, then web server will sends the HTTP response: Error 404 Not found.

When the web server searching the requested page if requested page is found then it will send to the client with an HTTP response.

If the client requests some other resources then web server will contact to application server and data is store for constructing the HTTP response.

Application Server

Application server contains Web and EJB containers. It can be used for servlet, jsp, struts, jsf, ejb etc.

It is a component based product that lies in the middle-tier of a server centric architecture.

It provides the middleware services for state maintenance and security, along with persistence and data access.

It is a type of server designed to install, operate and host associated services and applications for the IT services, end users and organizations.

Examples

The Example of Application Servers are:

JBoss: Open-source server from JBoss community.

Glassfish: Provided by Sun Microsystem. Now acquired by Oracle.

Weblogic: Provided by Oracle. It more secured.

Websphere: Provided by IBM.

Resources

Server: Web vs Application - javatpoint

Server is a device or a computer program that accepts and responds to the request made by other program, known as client. It is used to manage the network resources and for running the program or software that provides services. There are two types of servers: Web Server Application Server Web Server Web server contains only web or servlet container.

https://www.javatpoint.com/server-web-vs-application

Database Programming with JDBC

JDBC stands for Java Database Connectivity

It's a JAVA API to connect and execute the query with a database.

It's a part of the JAVA SE (Standard Edition)

JDBC API uses JDBC Drivers to connect with the database

Types of JDBC Drivers

JDBC-ODBC Bridge Driver,

Native Driver,

Network Protocol Driver, and

Thin Driver

with the help of JDBC API, we can save, update, delete and fetch data from the database

The java.sql package contains classes and interfaces for JDBC API

Popular Interfaces of JDBC API present in the java.sql package

Driver interface

Connection interface

Statement interface

PreparedStatement interface

CallableStatement interface

ResultSet interface

ResultSetMetaData interface

DatabaseMetaData interface

RowSet interface

Popular Classes of JDBC API present in the java.sql package

DriverManager class

Blob class

Clob class

Types class

Why Use JDBC ?

Previously ODBC API (which uses ODBC Drivers) written in C was used

So Java made its own API written in obviously Java to make it cohesive with the ecosystem

JDBC Drivers Deep Dive

JDBC Driver is a software component that enables java application to interact with the database

Types of JDBC Drivers

JDBC-ODBC Bridge Driver,

1) JDBC-ODBC bridge driver

In Java 8, the JDBC-ODBC Bridge has been removed.

Oracle does not support the JDBC-ODBC Bridge from Java 8. Oracle recommends that you use JDBC drivers provided by the vendor of your database instead of the JDBC-ODBC Bridge.

Advantages:

easy to use.

can be easily connected to any database.

Disadvantages:

Performance degraded because JDBC method call is converted into the ODBC function calls.

The ODBC driver needs to be installed on the client machine.

Native Driver,

2) Native-API driver

Advantage:

performance upgraded than JDBC-ODBC bridge driver.

Disadvantage:

The Native driver needs to be installed on each client machine.

The Vendor client library needs to be installed on client machine.

Network Protocol Driver, and

3) Network Protocol driver

The Network Protocol driver uses middleware (application server) that converts JDBC calls directly or indirectly into the vendor-specific database protocol. It is fully written in java.

Advantage:

No client side library is required because of application server that can perform many tasks like auditing, load balancing, logging etc.

Disadvantages:

Network support is required on client machine.

Requires database-specific coding to be done in the middle tier.

Maintenance of Network Protocol driver becomes costly because it requires database-specific coding to be done in the middle tier.

Thin Driver

4) Thin driver

Advantage:

Better performance than all other drivers.

No software is required at client side or server side.

Disadvantage:

Drivers depend on the Database.

Sir's Slides

Resources

JDBC Tutorial | What is Java Database Connectivity(JDBC) - javatpoint

JDBC stands for Java Database Connectivity. JDBC is a Java API to connect and execute the query with the database. It is a part of JavaSE (Java Standard Edition). JDBC API uses JDBC drivers to connect with the database.

https://www.javatpoint.com/java-jdbc

UNIT 4

Servlets

Terminology you need to understand

Web Server

Web server contains only web/servlet container.

It can be used for servlet, jsp, struts, jsf etc. It can't be used for EJB (Enterprise Java Bean needs application server).

It is a computer where the web content can be stored and installed with web server software like apache.

In general web server can be used to host the web sites but there also used as some other web servers also such as FTP, email, storage, gaming etc.

Types

Shared Web Server (Many websites hosted typically unrelated)
Dedicated Web Server ( opposite of shared )

Examples of Web Servers are: Apache Tomcat and Resin.

Application Server

An application server is a server that hosts applications.

It's a server application that implements the Java EE platform APIs and provides the standard Java EE services

Application server contains Web and EJB containers. It can be used for servlet, jsp, struts, jsf, ejb etc. It is a component based product that lies in the middle-tier of a server centric architecture.

It provides the middleware services for state maintenance and security, along with persistence and data access. It is a type of server designed to install, operate and host associated services and applications for the IT services, end users and organizations.

The block diagram representation of Application Server is shown below:

Web Container

A web container (also known as a servlet container) is the component of a web server that interacts with Servlets.

It's responsible for

Managing the lifecycle of servlets
Mapping a URL to a particular servlet
Ensuring that the URL requester has the correct access-rights.

It handles requests to servlets, Jakarta Server Pages (JSP) files, and other types of files that include server-side code.

It creates servlet instances, loads and unloads servlets, creates and manages request and response objects, and performs other servlet-management tasks.

It implements the web component contract of the Jakarta EE architecture.

This architecture specifies a runtime environment for additional web components, including security, concurrency, lifecycle management, transaction, deployment, and other services.

Servlets

A servlet is a Java program that runs on a Web server. It is similar to an applet, but is processed on the server rather than a client's machine.

A Servlet is a Java software component that extends the capabilities of a server.

Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applications on web servers and thus qualify as a server-side servlet web API

Picture representing relationship of all the above components

🗒️

Application Server is not needed for basic use but if specific Java EE Components have to be used, in that case applications servers are needed.

Web Server Vs Application Server

Web Container + HTTP request handling = Web Server

Web Server + EJB + (Messaging + Transactions+ etc) = Application Server

Features

In Servlets, when multiple requests are made, only one copy of servlet is loaded in Java Virtual Machine

In Servlets, for each request a thread is created rather than new process

Creating threads saves memory and response time

Servlet programs are persistent

Servlet API

Two java packages are used to implement Servlet API

javax.servlet ⭐

The javax.servlet package contains many interfaces and classes that are used by the servlet or web container.

These are not specific to any protocol.

Classes

GenericServlet

ServletInputStream

ServletOutputStream

ServletRequestWrapper

ServletResponseWrapper

ServletRequestEvent

ServletContextEvent

ServletRequestAttributeEvent

ServletContextAttributeEvent

ServletException

UnavailableException

Interfaces

Servlet

ServletRequest

ServletResponse

RequestDispatcher

ServletConfig

ServletContext

SingleThreadModel

Filter

FilterConfig

FilterChain

ServletRequestListener

ServletRequestAttributeListener

ServletContextListener

ServletContextAttributeListener

javax.servlet.http ⭐

The javax.servlet.http package contains interfaces and classes that are responsible for http requests only.

Classes

HttpServlet

HttpServletRequestWrapper

HttpServletResponseWrapper

HttpSessionEvent

HttpSessionBindingEvent

HttpUtils (deprecated now)

Interfaces

HttpServletRequest

HttpServletResponse

HttpSession

HttpSessionListener

HttpSessionAttributeListener

HttpSessionBindingListener

HttpSessionActivationListener

HttpSessionContext (deprecated now)

Servlet LifeCycle

Stages of the Servlet Life Cycle

Loading a Servlet.

Initializing the Servlet.

Request handling.

Destroying the Servlet.

Servlet Life Cycle Methods

init()

service()

destroy()

Diagram of methods

Pic 1

Pic 2

Further Reading

Life Cycle of a Servlet - GeeksforGeeks

The entire life cycle of a Servlet is managed by the Servlet container which uses the javax.servlet.Servlet interface to understand the Servlet object and manage it. So, before creating a Servlet object, let's first understand the life cycle of the Servlet object which is actually understanding how the Servlet container manages the Servlet object.

https://www.geeksforgeeks.org/life-cycle-of-a-servlet/

Life cycle of a servlet - javatpoint

The web container maintains the life cycle of a servlet instance. Let's see the life cycle of the servlet: Servlet class is loaded. Servlet instance is created. init method is invoked. service method is invoked. destroy method is invoked. As displayed in the above diagram, there are three states of a servlet: new, ready and end.

https://www.javatpoint.com/life-cycle-of-a-servlet

Sample Servlet

Session Tracking Mechanism

Session simply means a particular interval of time.

Session Tracking is a way to maintain state (data) of an user.

It is also known as session management in servlet.

Http protocol is a stateless so we need to maintain state using session tracking techniques. Each time user requests to the server, server treats the request as the new request. So we need to maintain the state of an user to recognize to particular user.

HTTP is stateless that means each request is considered as the new request.

Session Tracking Techniques

Cookies

A cookie is a small piece of information that is persisted between the multiple client requests.

A cookie has a name, a single value, and optional attributes such as a comment, path

By default, each request is considered as a new request. In cookies technique, we add cookie with response from the servlet.

So cookie is stored in the cache of the browser. After that if request is sent by the user, cookie is added with request by default. Thus, we recognize the user as the old user.

There are two types of cookies

Non-persistant Cookies (Valid for single session)

Persistant Cookies (Valid for multiple Sessions)

Advantages

Simplest technique of maintaining the state.

Cookies are maintained at client side.

Disadvantages

It will not work if cookie is disabled from the browser.

Only textual information can be set in Cookie object.

There are 3 Types of directives

Page Directive

<%@ page attribute="value" %>

It provides attributes that get applied to entire JSP page.

It defines page dependent attributes, such as scripting language, error page, and buffering requirements.

It is used to provide instructions to a container that pertains to current JSP page.

Following are its list of attributes associated with page directive:

To see detail about these attributes head over to the resource toggle below

Language

Extends

Import

contentType

info

session

isThreadSafe

autoflush

buffer

IsErrorPage

pageEncoding

errorPage

isELIgonored

Example

<%@ page language="java" %>

Include Directive

<%@ include….%>

JSP "include directive" is used to include one file to the another file

This included file can be HTML, JSP, text files, etc.

It is also useful in creating templates with the user views and break the pages into header&footer and sidebar actions.

It includes file during translation phase

Example Syntax of include directive:

<%@page import="java.util.Date" %>

Taglib Directive

<%@ taglib uri="uri" prefix="myTag"%>

JSP taglib directive is used to define the tag library with "taglib" as the prefix, which we can use in JSP.

Basically if you have tags which are custom made for your project you can use that with this directive

JSP taglib directive is used in the JSP pages using the JSP standard tag libraries

It uses a set of custom tags, identifies the location of the library and provides means of identifying custom tags in JSP page.

Syntax of taglib directive:

<%-- Initialize custom tag like this %-->

<%@ taglib uri="uri" prefix="value"%>

<%-- Use the tag like this %-->

<mytag:currentDate/>

Here "uri" attribute is a unique identifier in tag library descriptor and "prefix" attribute is a tag name.

Resource

JSP Directives: Page, Include & Taglib Tutorial

JSP directives are the messages to JSP container. They provide global information about an entire JSP page. JSP directives are used to give special instruction to a container for translation of JSP to servlet code. In JSP life cycle phase, JSP has to be converted to a servlet which is the translation phase.

https://www.guru99.com/jsp-actions.html

JSP Implicit Objects

JSP implicit objects are created during the translation phase of JSP to the servlet.

These objects can be directly used in scriplets that goes in the service method.

They are created by the container automatically, and they can be accessed using objects.

How many Implicit Objects are available in JSP?

There are 9 types of implicit objects available in the container:

To see detail about these implicit objects click here and go to the resource website

out

Out is one of the implicit objects to write the data to the buffer and send output to the client in response

Out object allows us to access the servlet's output stream

Out is object of javax.servlet.jsp.jspWriter class

While working with servlet, we need printwriter object

Example where JSP page converted into servlet

Notice the PrintWriter class

request

The request object is an instance of java.servlet.http.HttpServletRequest and it is one of the argument of service method

It will be created by container for every request.

It will be used to request the information like parameter, header information , server name, etc.

It uses getParameter() to access the request parameter.

response

"Response" is an instance of class which implements HttpServletResponse interface

Container generates this object and passes to _jspservice() method as parameter

"Response object" will be created by the container for each request.

It represents the response that can be given to the client

The response implicit object is used to content type, add cookie and redirect to response page

config

"Config" is of the type java.servlet.servletConfig

It is created by the container for each jsp page

It is used to get the initialization parameter in web.xml

application

Application object is an instance of javax.servlet.ServletContext and it is used to get the context information and attributes in JSP.

Application object is created by container one per application, when the application gets deployed.

Servletcontext object contains a set of methods which are used to interact with the servlet container.We can find information about the servlet container

session

The session is holding "httpsession" object(code line 10).

Session object is used to get, set and remove attributes to session scope and also used to get session information

pageContext

This object is of the type of pagecontext.

It is used to get, set and remove the attributes from a particular scope

There are 4 types of Scopes

Page

Request

Session

Application

<% pageContext.setAttribute("student","gurustudent",pageContext.PAGE_SCOPE); %>

setAttribute has 3 parameters :

Value

Scope

page

Page implicit variable holds the currently executed servlet object for the corresponding jsp.

Acts as this object for current jsp page.

<% String pageName = page.toString(); %>

exception

Exception is the implicit object of the throwable class.

It is used for exception handling in JSP.

The exception object can be only used in error pages

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"

🗒️

Explanation : It has an array of numbers, i.e., num1 with four elements. In the output, we are trying to print the fifth element of the array from num1, which is not declared in the array list. So it is used to get or show exception object of the jsp.

Output

Resource

www.guru99.com

https://www.guru99.com/jsp-implicit-objects.html

JSP Standard Action Tags

What is JSP Action?

JSP actions use the construct in XML syntax to control the behavior of the servlet engine.

We can dynamically insert a file, reuse the beans components, forward user to another page, etc. through JSP Actions like include and forward.

Unlike directives, actions are re-evaluated each time the page is accessed.

Syntax:

<jsp:action_name attribute="value" />

How many Action Tags are available in JSP ?

There are 11 types of Standard Action Tags as following:

To see detail about these implicit objects click here

jsp:useBean

jsp:include

jsp:setProperty

jsp:getProperty

jsp:forward ⭐

It is used to forward the request to another jsp or any static page.

Here the request can be forwarded with no parameters or with parameters.

Syntax:

<jsp:forward page="value">

Here value represents where the request has to be forwarded.

Example:

Action_jsp41.jsp

	<%@ page language="java" contentType="text/html; charset=ISO-8859-1"    pageEncoding="ISO-8859-1"%>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
		<head>
			<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
			<title>Guru Action JSP1</title>
		</head>
		<body>
			<jsp:forward page="jsp_action_42.jsp" />  --- [ <-- LINE 10 ] ---
		</body>
	</html>

Jsp_action_42.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
	<title>Guru Action JSP2</title>
</head>
<body>
	<a>This is after forward page</a>
</body>
</html>

Explanation of the code

Action_jsp41.jsp

Code Line 10: Here we are using forward JSP Action to forward the request to the page mentioned in the attribute, i.e., jsp_action_42.jsp

Jsp_action_42.jsp

Code Line 10: Once we call action_jsp41.jsp, the request gets forwarded to this page, and we get the output as "This is after forward page."

When we execute the above code, we get the following output

Output:

We call action_jsp41.jsp but the request gets forwarded to jsp_action_42.jsp, and we get the output from that page as "This is after forward page".

jsp:plugin

jsp:attribute

jsp:body

jsp:text

jsp:param

jsp:attribute

jsp:output

Resource

JSP Standard Action Tags: include, useBean, forward, param

JSP actions use the construct in XML syntax to control the behavior of the servlet engine. We can dynamically insert a file, reuse the beans components, forward user to another page, etc. through JSP Actions like include and forward. Unlike directives, actions are re-evaluated each time the page is accessed.

http://guru99.com/jsp-action-tags.html

JSP Expression Language

What is Expression Language (EL)?

( Enables you to directly execute code in the JSP file )

Expression Language (EL) is mechanism that simplifies the accessibility of the data stored in Java bean component and other object like request, session and application, etc.

There are many operators in JSP that are used in EL like arithmetic and logical operators to perform an expression. It was introduced in JSP 2.0

In this tutorial, you will learn-

JSP Syntax of Expression Language (EL)

Syntax of EL :$(expression)

In JSP, whatever present in the braces gets evaluated at runtime sent to the output stream.

The expression is a valid EL expression and it can be mixed with a static text and can be combined with other expression to form larger expression.

To get a better idea, on how expression works in JSP, we will see below example.

In this example, we will see how EL is used as an operator to add two numbers (1+2) and get the output respectively.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"	pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
		<title>Guru JSP1</title>
	</head>
	<body>
		<a>Expression is:</a>
		${1+2};
	</body>
</html>

Explanation of Code:

Code Line 11: Expression Language (EL) is set where we are adding two numbers 1+2, hence it will give output as 3.

When you execute the above code, you will have the following Output.

Output:

Expression is: 3 (As numbers 1+2 will be added and serve as an output)

Flow - Control Statements

Decision-Making Statements

JSP If-else

"If else" statement is basic of all control flow statements, and it tells the program to execute the certain section of code only if the particular test evaluates to true.

This condition is used to test for more than one condition whether they are true or false.

If the first condition is true then "if block" is executed and

if it is false then "else block" is executed

Syntax for if – else statement:

If(test condition)
{
	 //Block of statements
}
else
{
    //Block of statements

JSP Switch

The body of the switch statement is called as a "switch block".

The switch case is used to check the number of possible execution paths.

A switch can be used with all data types

The switch statements contain more than one cases and one default case

It evaluates the expression then executes all the statements following the matching case

Syntax for switch statement:

switch (operator)
{
   Case 1:
       Block of statements
break;
   Case 2:
      Block of statements
break;


case n:
    Block of statements
break;
default:
  Block of statements
break;
}

Switch block begins with one parameter, which is the operator that needs to be passed and

Then there are different cases which provides condition and whichever matches with the operator that case is executed.

Loop Statements

JSP For loop

It is used for iterating the elements for a certain condition, and it has three parameters.

Variable counter is initialized

Condition till the loop has to be executed

Counter has to be incremented

For loop Syntax:

For(inti=0;i<n;i++)
{
           //block of statements
}

JSP While loop

It is used to iterate the elements wherein it has one parameter of the condition.

Syntax:

While(i<n)
{
      //Block of statements
}

JSP Operators

JSP Operators supports most of its arithmetic and logical operators which are supported by java within expression language (EL) tags.

JSP Custom Tags

Custom Tags in JSP - javatpoint

Custom tags are user-defined tags. They eliminates the possibility of scriptlet tag and separates the business logic from the JSP page. The same business logic can be used many times by the use of custom tag.

https://www.javatpoint.com/custom-tags

Directory Structure of JSP

In directory structure, there is a root folder which has folder WEB-INF, which has all configuration files and library files.

JSP files are outside WEB-INF folder

JSP vs Java Servlet

Acessing database from Servlet and JSP

JSP - Database Access

JSP - Database Access - In this chapter, we will discuss how to access database with JSP. We assume you have good understanding on how JDBC application works. Before starting with data

https://www.tutorialspoint.com/jsp/jsp_database_access.htm

Architecture of JSP Page

JSP - Architecture

The web server needs a JSP engine, i.e, a container to process JSP pages. The JSP container is responsible for intercepting requests for JSP pages. This tutorial makes use of Apache which has built-in JSP container to support JSP pages development.

https://www.tutorialspoint.com/jsp/jsp_architecture.htm

Resources

JSP Tutorial for Beginners: Learn in 7 Days

Training Summary JSP (JavaServer Page) is a Java based server side programming language used for developing web-based applications. In this tutorial, you will learn various concept of JSP like Java Servlets

https://www.guru99.com/jsp-tutorial.html

JSP Tutorial

JSP Tutorial - Java Server Pages (JSP) is a server-side programming technology that enables the creation of dynamic, platform-independent method for building Web-based applica

https://www.tutorialspoint.com/jsp/index.htm

Learn JSP Tutorial - javatpoint

JSP technology is used to create web application just like Servlet technology. It can be thought of as an extension to Servlet because it provides more functionality than servlet such as expression language, JSTL, etc. A JSP page consists of HTML tags and JSP tags.

https://www.javatpoint.com/jsp-tutorial

Sir's PPTs