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JAVA SERVLETSJAVA SERVLETS

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Web ServerA web server is a network server that

manages access to files, folders and other resources over Internet or local Intranet via HTTP ◦ Handle permissions◦ Execute programs◦ Keep track of directories and files◦ Communicate with client computers

A web server consists of a computer with:◦ a suitable operating system◦ a suitable file system◦ a network connection◦ web server software – which accepts requests

from browsers such as IE and Netscape

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Web Server ………A Web server handles the HTTP protocol.

When the Web server receives an HTTP request, it responds with an HTTP response, such as sending back an HTML page.

To process a request, a Web server may respond with a HTML page or image, send a redirect, or delegate the dynamic response generation to some other program such as CGI scripts, JSPs (JavaServer Pages), servlets, ASPs (Active Server Pages), server-side JavaScripts, or some other server-side technology.

such server-side programs generate a response, most often in HTML, for viewing in a Web browser.

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Web Server ……..Web server's delegation model is fairly simple.

When a request comes into the Web server, the Web server simply passes the request to the program best able to handle it.

The Web server doesn't provide any functionality beyond simply providing an environment in which the server-side program can execute and pass back the generated responses.

The server-side program usually provides for itself such functions as transaction processing, database connectivity, and messaging.

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Web Server …….

While a Web server may not itself support transactions or database connection pooling, it may employ various strategies for fault tolerance and scalability such as load balancing, caching, and clustering—features oftentimes erroneously assigned as features reserved only for application servers

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Web ArchitectureMulti-tier architecture:

◦ Application-level or middleware: has an application server, which is used to find requested data and services, makes them available for viewing, and carries out transactions.

◦ Data and service level: has a variety of data and services accessible by the application server.

Databaseserver

Client computers with web browsers

Web server

Internet

HTTP request

HTTP response

Presentation level

Content level Data and service level

Application server

Application level

Billing system

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Application Server Application server exposes business

logic to client applications through various protocols, including HTTP.

Application server provides access to business logic for use by client application programs. The application program can use this logic just as it would call a method on an object (or a function in the procedural world).

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Application ServerApplication server clients can include

GUIs (running on a PC, a Web server, or even other application servers.

The information traveling back and forth between an application server and its client is not restricted to simple display markup.

Instead, the information is program logic. Since the logic takes the form of data and method calls and not static HTML, the client can employ the exposed business logic however it wants.

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Application Server In most cases, the server exposes this

business logic through a component API, such as the EJB (Enterprise JavaBean) component model found on J2EE (Java 2 Enterprise Edition) application servers.

Moreover, the application server manages its own resources that include security, transaction processing, resource pooling, and messaging.

Like a Web server, an application server may also employ various scalability and fault-tolerance techniques.

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Application Server

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Web servers Web servers

Internet Information Server

Personal Web Server

Java Web Server

Apache Tomcat Server

Web Logic

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Tomcat web serverTomcat web serverFor the deployment the steps are to be

followed:

1. Put the source code for the servlet in the Server_root/webapps/ROOT/WEB-INF/classes

directoryThis is a standard location for servlet class files.2. Include server_root /lib/servlet.jar somewhere

in class path so that the two packages will be included in the class path.

3. Compile the servlet using javac filename.java4. After compiling start the server by looking the

startup.sh script in the server root/bin directory

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To access the servlet, type the URL in the browser as (if the server is on the local machine)

http://localhost :8080/servlet/passwordcheck.

Tomcat web serverTomcat web server

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Introduction to servletsIntroduction to servletsServlet runs on the server and will

respond to a request from the client either in the form of HTML pages, dynamic pages or indeed applets.