Servlet 01

Objectives In this lesson, you will learn to: Identify the characteristics of a Servlet Create a Servlet Deploy a Servlet

Need for Servlets Servlets are required to: Reduce the overhead on the server and network To take care of processing data on the Web server

Servlets are: Java programs that can be deployed on a Java enabled Web server Used to extend the functionality of a Web server Used to add dynamic content to Web pages

Characteristics of Servlets Servlets are: Efficient Initialization code for a servlet is executed only once Robust Provide all powerful features of Java

Portable across Web servers Persistent Increase the performance of a system by preventing frequent disk access

Comparison between Servlets and Applets Applets: Are embedded in Web pages Require the browser to be Java-enabled Take a lot of time to be downloaded

Servlets: Execute on the Web server, thus help overcome problems with download time Do not require the browser to be Java-enabled

Comparison between Servlets and other Server- Side Scripting Technologies Common Gateway Interface (CGI) scripts, JSP, and ASP are alternatives to servlets CGI Scripts: Are programs written in C, C++, or Perl Get executed in a server Run in separate processes for each client access Require the interpreter to be loaded on the server A JSP file is automatically converted to a servlet before it is executed

Comparison between Servlets and other Server- Side Scriptings Active Server Pages (ASP): Is a server-side scripting language developed by Microsoft Enables a developer to combine HTML and a scripting language in the same Web page Are not compatible with all Web servers

Working of Servlets Client browser passes requests to a servlet using the following methods: GET Uses a query string to send additional information to the server Query string is displayed in the client browser

POST Sends the data as packets to the server through a separate socket connection Complete transaction is invisible to the client Slower compared to the GET method

The javax.servlet Package Hierarchy of classes that are used to create a servlet Class java.lang.Object Class javax.servlet.GenericServlet Class javax.servlet.HttpServlet Interface javax.servlet.Servlet Interface javax.servlet.ServletConfig Interface javax.io.Serializable

The javax.servlet Package (Contd.) A brief description of the classes and interfaces Provides methods to process requests from the clients. HTTPServletRequest interface Provides a HTTP specific implementation of the Servlet interface. HTTPServlet class Description Class/Interface

Response to the client is sent in the form of a HTML page through an object of the HTTPServletResponse class. HTTPServlet Response interface Used to store the servlets startup configuration values and the initialization parameters. ServletConfig class

Life Cycle of a Servlet Life cycle of a servlet: Client (Browser) init() service() destroy() Request Response

Life Cycle of a Servlet (Contd.) The following table describes few methods that are used in creating a servlet: Receives all requests from clients, identifies the type of the request, and dispatches them to the doGet() or doPost() methods for processing. Servlet. service() Contains all initialization code for the servlet. Servlet.init (ServletConfig config) throws ServletException Functionality Method name

Life Cycle of a Servlet (Contd.) Executes only once when the servlet is removed from server. Servlet. destroy() Sets the type of content that is to be sent as response to the client browser. HTTPServlet Response. setContentType (String type) Returns a reference to a PrintWriter object. HTTPServlet Response. getWriter() Functionality Method name

Deploying a Servlet A servlet can be deployed in: Java Web Server (JWS) JRun Apache Java 2 Enterprise Edition (J2EE) server

Identify the mechanism to record the number of hits on a Web site Client browsers that are used to access the Web site run on different machines Hence, the client (browser) cannot keep track of the hit count data This data has to be captured on the server’s side Thus, a technique that can be used to write a server-side program is necessary to solve this problem

Identify the classes to be used A class that extends the HttpServlet class must be coded to solve the problem

Identify the methods to be used The init() method needs to be coded in the hitcountServlet class to initialize the hitcounter to zero The doGet() method needs to be coded to increment the hit counter whenever a client browser makes a request for the site home page

Write and compile the servlet Set the values of PATH and CLASSPATH variables Code the servlet program Compile the program by using the command javac hitcountServlet.java

Execute the servlet Type http://127.0.0.1:8000/hitcountwebcontext/hitcounter in the address bar of the browser to execute the servlet

Problem for you…. In the URL that is provided, identify the Web context name and the alias name of the servlet http://127.0.0.1:8000/name/execute

Summary In this lesson, you learned that: Servlets are server-side Java programs that can be deployed on a Web Server The Servlet interface provides the basic framework for coding servlets

Servlets are : Portable Extensible Persistent Robust

Summary (Contd.) The life cycle of a servlet is composed of the init() , service() , and the destroy() methods Servlets can be deployed in the J2EE server and JWS The deploytool command is used to deploy a servlet on a J2EE server

Servlet 01

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Servlet 01