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In the recent trends, a billion bytes of data is generated on a day-to-day basis. Most of us believe in the misconception that all of the web applications are created over web frameworks like HTML, PHP, JavaScript etc. But, did you know, web applications can be based on Java using services like Servlets and JSP? In this Servlet and JSP Tutorial, let's delve deep into the technology and understand how it is useful for creating a web application.

Below is the list of topics that I will be covering in this Servlet and JSP tutorial

• • Servlet
    • Web & HTTP
    • Introduction to Servlets
    • Servlet Life Cycle
    • Steps to Create Servlets
    • Session Tracking
    • Cookies
  • JSP
    • Introduction to JSP
    • JSP vs Servlets
    • JSP Scripting Elements
    • JSP Request and Response

You may also go through this recording of  Servlet and JSP Tutorial where you can understand the topics in a detailed manner with examples.

Servlet Tutorial | JSP Tutorial | Advanced Java Tutorial | Edureka

This Edureka tutorial on "Servlet and JSP tutorial" will talk the fundamental concepts of servlets and JSP, its life cycle and various steps to create Servlet and Java Server Pages.

Servlet and JSP Tutorial: Web & HTTP

Web is a system ofInternetservers that supports formatted documents. The documents are formatted using a markup language called HTML (HyperText Markup Language) that supports links to other documents like graphics, audio, and video files etc.

Now that we know what is web,  let's move further and understand what is a website. So, a website is a collection of static files i.e. web pages like HTML pages, images, graphics etc. And,the Web application is a website with dynamic functionality on the server.Google,Facebook,Twitter  are examples of web applications.

So, what is the link between the Web and HTTP? Let's now find out.

HTTP (Hypertext Transfer Protocol)

HTTP is used by clients and servers to communicate on the web. It is considered asa stateless protocol because it supports only one request per connection. With HTTP the clients connect to the server to send one request and then disconnect. And this mechanism allows more users to connect to a given server over a period of time. Here, the client sends an HTTP request and the server answers with an HTML page to the client, using HTTP.

That was all about HTTP and Web. Now let's dive deep into Servlets and understand its working mechanism.

Introduction to Servlets

Servlet is a server-side Java program module that handles client requests and implements theservlet interface. Servlets can respond to any type of request, and they are commonly used to extend the applications hosted by web servers.

In this figure you can see, a client sends a request to the server and the server generates the response, analyses it and sends the response back to the client.

Now, let's jump into the next concept and understand Servlet Life Cycle.

Servlet Life Cycle

The entire life cycle of a servlet is managed by theServlet container which uses thejavax.servlet.Servlet interface to understand the Servlet object and manage it.

 Servlet Life Cycle: The Servlet life cycle mainly goes through four stages:

• Loading a Servlet

When a server starts up, the servlet container deploy and loads all the servlets.

• Initializing the Servlet

Next, a servlet is initialized by calling the init() method.Servlet.init()method is called by the Servlet container to notify that this Servlet instance is instantiated successfully and is about to put into service.

• Request handling

Then, servlet callsservice()method to process a client's request and is invoked to inform the Servlet about the client requests.

• Destroying the servlet

Finally, a servlet is terminated by calling thedestroy(). The destroy() method runs only once during the lifetime of a Servlet and signals the end of the Servlet instance.

init() and destroy() methods are called only once. Finally, a servlet is garbage collected by the garbage collector of the JVM. So this concludes the life cycle of a servlet. Now, let me guide you through the steps of creating Java servlets.

 Servlet and JSP Tutorial: Steps to Create Servlet

In order to create a servlet, we need to follow a few steps in order. They are as follows:

1. Create a directory structure
2. Create a Servlet
3. Compile the Servlet
4. Add mappings to the web.xml file
5. Start the server and deploy the project
6. Access the servlet

Now, based on the above steps, let's create a program to understand better, how a servlet works.

To run a servlet program, we should have Apache Tomcat Server installed and configured.Eclipse for Java EE provides in-built Apache Tomcat. Once the server is configured, you can start with your program. One important point to note – for any servlet program, you need 3 files –index.html file, Java class file, and web.xml file. The very first step is to create a Dynamic Web Project and then proceed further.

Now, let's take an example where I will be creating a simple login servlet and display the output in the browser.

First,  I will create index.html file

<!DOCTYPE html> <html> <body>  <form action="Login" method="post">  <table>  <tr>  <td>Name:</td>   <td><input type="text" name="userName"></td>  </tr>   <tr>  <td>Password:</td>   <td><input type="password" name="userPassword"></td>  </tr>  </table>  <input type="submit" value="Login"> </form>  </body> </html>        

Next, let's code the Java Class file.

package Edureka; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest import javax.servlet.http.HttpServletResponse; public class Login extends HttpServlet { protected void doPost(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException PrintWriter pw=res.getWriter(); res.setContentType("text/html"); String user=req.getParameter("userName"); String pass=req.getParameter("userPassword"); pw.println("Login Success...!") if(user.equals("edureka") && pass.equals("edureka")) pw.println("Login Success...!"); else pw.println("Login Failed...!"); pw.close(); } }        

In the above code, I have set a condition – if username and password are equal to edureka,  only then it will display successfully logged in, else login will be denied. After writing the Java class file, the last step is to add mappings to the web.xml file. Let's see how to do that.

Theweb.xml file will be present in the WEB-INF folder of your web content. If it is not present, then you can click on Deployment Descriptor and click onGenerate Deployment Descriptor Stub.Once you get your web.xml file ready, you need to add the mappings to it. Let's see how mapping is done using the below example:

<?xml version="1.0"encoding="UTF-8"?> <web-app xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance">http://www.w3.org/2001/XMLSchema-instance</a>" xmlns="<a href="http://xmlns.jcp.org/xml/ns/javaee">http://xmlns.jcp.org/xml/ns/javaee</a>"xsi:schemaLocation="<a href="http://xmlns.jcp.org/xml/ns/javaee">http://xmlns.jcp.org/xml/ns/javaee</a> <a href="http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd</a>"version="3.1"> <display-name>LoginServlet</display-name> <servlet> <servlet-name>Login</servlet-name> <servlet-class>Edureka.Login</servlet-class> </servlet> <servlet-mapping> <servlet-name>Login</servlet-name> <url-pattern>/Login</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.html</welcome-file> </welcome-file-list> </web-app>        

So, this is how a servlet is created and configured. Let's now see what a Generic servlet is and how is it created.

Generic Servlets

It is a protocol-independent servlet that should override the service() method to handle the client request. The service() method accepts two arguments,ServletRequest object, and ServletResponse object. Work of request object is to inform the servlet about the request made by the client while the response object returns a response back to the client. GenericServlet is anabstract class and it has only one abstract method, which isservice(). That's the whole concept when we create a Generic Servletby extending the GenericServlet class, we must override the service() method.

Now, let's see how to create and invoke a Generic servlet. Again I will code 3 files as shown below:

 HTML file

We are creating an HTML file that will call the servlet once we click on the link on the web page. Create this file in the WebContent folder. The path of this file should look like this: WebContent/index.html

<html> <title>Generic Servlet Demo</title> </head> <body> <a href="welcome">Click here to call Generic Servlet</a> </body> </html>        

Java Class file

Here we will be creating a Generic Servlet by extending GenericServlet class. When creating a GenericServlet, you must override the service() method. Right click on thesrc folder and create a new class file and name the file as generic. The file path should look like this: Java Resouces/src/default package/generic.java

package EdurekaGeneric; import java.io.*; importjavax.servlet.*; public class generic extends GenericServlet{ public void service(ServletRequest req,ServletResponse res) throws IOException,ServletException{ res.setContentType("text/html"); PrintWriter pwriter=res.getWriter(); pwriter.print("<html>"); pwriter.print("<body>"); pwriter.print(" <h2>Generic Servlet Example</h2>  "); pwriter.print("Welcome to Edureka YouTube Channel"); pwriter.print("</body>"); pwriter.print("</html>"); } }        

 web.xml
This file can be found at this path WebContent/WEB-INF/web.xml. In this file, we will map the Servlet with the specific URL. Since we are calling the welcome page upon clicking the link onindex.html, it will map the welcome page to the Servlet class that we have already created above.

<servlet> <servlet-name>MyGenericServlet</servlet-name> <servlet-class>EdurekaGeneric.generic</servlet-class> </servlet> <servlet-mapping> <servlet-name>MyGenericServlet</servlet-name> <url-pattern>/welcome</url-pattern> </servlet-mapping>        

After this, start your Tomcat Server and run the servlet. You will get the desired output. So this was all about Generic Servlets. Now let's move further and understand the concept of session tracking.

Servlet and JSP Tutorial: Session Tracking

Sessionsimply means a particular interval of time. Session trackingis a technique to maintain state (data) of a user also known assession management in servlet. So, each time user requests to the server, the server treats the request as the new request.

Below figure depicts how each request from the client is considered as a new request.

In order to recognize the particular user, we need session tracking. Now let's move further and see one of the techniques of session tracking i.e. Cookies.

Servlet and JSP Tutorial: Cookies

Acookie 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 and domain qualifiers, a maximum age, and a version number.

How Does Cookie Work?

As it is a technique of Session tracking, by default, each request is considered as a new request.

In this, we add a cookie with the response from the servlet. So the cookie is stored in the cache of the browser. After that, if a request is sent by the user, a cookie is added with the request by default.

Now as you have understood how cookie works, let see a small example illustrating the use of cookies.

Let's see an example of creating a cookie, adding the response and retrieving the results. Here I will be writing 2 java class files i.e MyServlet1 and MyServlet2.

File: MyServlet1

package Edureka; import java.io.*; import javax.servlet.*; import javax.servlet.annotation.WebServlet; import javax.servlet.http.*; @WebServlet("/login") public class MyServlet1 extends HttpServlet{ public void doGet(HttpServletRequest request,&nbsp; HttpServletResponse response) { try{ response.setContentType("text/html"); PrintWriter pwriter = response.getWriter(); String name = request.getParameter("userName"); String password = request.getParameter("userPassword"); pwriter.print("Hello here:"+name); pwriter.print(" Your Password is: "+password); //Creating two cookies Cookie c1=new Cookie("userName",name); Cookie c2=new Cookie("userPassword",password); //Adding the cookies to response header response.addCookie(c1); response.addCookie(c2); pwriter.print(" <a href='welcomehere'>View Details</a>"); pwriter.close(); }catch(Exception exp){ System.out.println(exp); } } }        

File: MyServlet2

package Edureka; import java.io.*; import javax.servlet.*; import javax.servlet.annotation.WebServlet; import javax.servlet.http.*; @WebServlet("/welcomehere") public class MyServlet2 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response){ try{ response.setContentType("text/html"); PrintWriter pwriter = response.getWriter(); //Reading cookies Cookie[] c=request.getCookies(); //Displaying User name value from cookie pwriter.print("Name here: "+c[0].getValue()); pwriter.print("Password: "+c[1].getValue()); //pwriter.print(" <a href='welcome'>View Details</a>"); pwriter.close(); }catch(Exception exp){ System.out.println(exp); } } }        

Now, let's create a simple HTML form for cookies.

<!DOCTYPE html> <html> <body> <body>  <form action="login"> User Name:<input type="text" name="userName"/> Password:<input type="password" name="userPassword"/> <input type="submit" value="submit"/> </form>  </body> </html>        

Now, the last step is to create XML file and add all the mappings to it.

<servlet> <servlet-name>Servlet1</servlet-name> <servlet-class>Edureka.MyServlet1</servlet-class> </servlet> <servlet-mapping> <servlet-name>Servlet1</servlet-name> <url-pattern>/login</url-pattern> </servlet-mapping> <servlet> <servlet-name>Servlet2</servlet-name> <servlet-class>Edureka.MyServlet2</servlet-class> </servlet> <servlet-mapping> <servlet-name>Servlet2</servlet-name> <url-pattern>/welcomehere</url-pattern> </servlet-mapping>        

Now you are all set for execution. You can run the code and get the desired output. This is how a cookie works. So that was all about Servlets. If you ish to learn Advance Java in depth, you can refer to this Advanced Java Tutorial. Now that you have gained some insights on Servlets, let's move ahead and understand what is Java Server Pages.

Servlet and JSP Tutorial: Java Server Pages

JSP or Java Server Pages is a technology that is used to create web application just like Servlet technology. It is an extension to Servlet – as it provides more functionality than a servlet such as expression language, JSTL, etc. A JSP page consists of HTML tags and JSP tags. The JSP pages are easier to maintain than Servlet because we can separate designing and development.

Now, as we know what JSP is, let's compare JSP with Servlets and understand which is best suitable for the web.

Servlet and JSP Tutorial: Advantages of JSP Over Servlets

JSP	Servlets
Extension to Servlet	Not an extension to servlet
Easy to Maintain	Bit complicated
No need to recompile or redeploy	The code needs to be recompiled
Less code than a servlet	More code compared to JSP

I hope you understood the difference between JSP and Servlets. Now, let's move further and understand Scripting elements.

Servlet and JSP Tutorial: JSP Scripting Elements

The scripting elements provide the ability to insert java code inside the JSP. There are three types of scripting elements:

• scriptlet tag–  A scriptlet tag is used to execute Java source code in JSP.

                Syntax : <%  java source code %>            

In this example, we have created two files index.html and welcome.jsp. The index.html file gets the username from the user and the welcome.jsp file prints the username with the welcome message. Now, let's look at the code.

File: index.html

<html> <body> <form&nbsp;action="welcome.jsp"> <input&nbsp;type="text"&nbsp;name="uname"> <input&nbsp;type="submit"&nbsp;value="go"> </form>  </body> </html>        

File: welcome.jsp

<html> <body> <% String&nbsp;name=request.getParameter("uname"); print("welcome&nbsp;"+name); %> </form>  </body> </html>        

• expression tag– The code placed withinJSP expression tagiswritten to the output stream of the response. So you need not write out.print() to write data. It is mainly used to print the values of variable or method.

                Syntax : <%=  statement %>            

Now let's take a small example of displaying the current time.  To display the current time, we have used the getTime() method of Calendar class. The getTime() is an instance method of Calendar class, so we have called it after getting the instance of Calendar class by the getInstance() method.

File: index.jsp

<html> <body> Current&nbsp;Time:&nbsp;<%=&nbsp;java.util.Calendar.getInstance().getTime()&nbsp;%> </body> </html>        

• declaration tag– The JSP declaration tag is usedto declare fields and methods. The code written inside the JSP declaration tag is placed outside the service() method of an auto-generated servlet. So it doesn't get memory at each request.

                Syntax: <%!  field or method declaration %>            

In the below example of JSP declaration tag, we are defining the method which returns the cube of a given number and calling this method from the JSP expression tag. But we can also use JSP scriptlet tag to call the declared method. Let's see how.
File: index.jsp

<html> <body> <%! int&nbsp;cube(int&nbsp;n){ return&nbsp;n*n*n*; } %> <%=&nbsp;"Cube&nbsp;of&nbsp;3&nbsp;is:"+cube(3)&nbsp;%> </body> </html>        

So, this is all about JSP Scripting Elements.  Now let's move ahead and see request and response objects of JSP.

Servlet and JSP Tutorial: JSP Request and Response Objects

JSP request is an implicit object of type HttpServletRequest that is created for each JSP request by the web container. It can be used to get request information such as a parameter, header information, remote address, server name, server port, content type, character encoding etc. It can also be used to set, get and remove attributes from the JSP request scope.

Let's see the simple example of request implicit object where we are printing the name of the user with a welcome message. Let's see how.

Example of JSP request implicit object

File: index.html

<form&nbsp;action="welcome.jsp"> <input&nbsp;type="text"&nbsp;name="uname"> <input&nbsp;type="submit"&nbsp;value="go"> </form>        

File: welcome.jsp

<% String&nbsp;name=request.getParameter("uname"); print("welcome&nbsp;"+name); %>        

JSP response implicit object

In JSP, the response is an implicit object of type HttpServletResponse. The instance of HttpServletResponse is created by the web container for each JSP request. It can be used to add or manipulate responses such as redirect response to another resource, send error etc.

Let's see the example of response implicit object where we are redirecting the response to Google.

Example of response implicit object

File: index.html

<form&nbsp;action="welcome.jsp"> <input&nbsp;type="text"&nbsp;name="uname"> <input type="submit"&nbsp;value="go"> </form>        

File: welcome.jsp

<% sendRedirect("http://www.google.com"); %>        

So, this is how request and response objects work. This brings to the end of Servlet and JSP tutorial article. I hope this blog was informative and added value to your knowledge.

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Source: https://www.edureka.co/blog/servlet-and-jsp-tutorial/