JAVA EE: Servlets : Send Redirect Demo[Transfer control to the Servlet which is in the Same Webcontainer]

Sunday, 4 May 2014

Servlets : Send Redirect Demo[Transfer control to the Servlet which is in the Same Webcontainer]

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What is Send Redirect in Java Servlets?

In Java web applications, sendRedirect is a mechanism provided by the HttpServletResponse interface that redirects a client browser to a different resource. Unlike request forwarding, which occurs entirely on the server side, a redirection involves communication between the client (browser) and the server.

When you call response.sendRedirect("url"), the servlet container sends an HTTP response back to the browser with an HTTP status code 302 (Found) along with a Location header containing the destination URL. Upon reading this response, the browser automatically sends a brand new GET request to the specified URL.

How Control Transfers Within the Same Web Container

In this demonstration, control is transferred between two servlets hosted inside the same Tomcat web container:

LoginServlet (mapped to /login): Handles incoming user credentials submitted via a POST request from index.html.
WelcomeServlet (mapped to /welcome): Welcomes authenticated users and displays output directly to the browser.

When valid credentials are provided, LoginServlet invokes:

response.sendRedirect("welcome");

The browser receives status code 302, detects the target location http://localhost:8080/sendredirectdemo/welcome, and initiates a clean GET request to display the welcome screen.

Key Takeaways

Two Requests & Two Responses: Redirection requires two distinct round-trips between the client and server.
URL Updates in the Browser: The browser address bar updates to show the target resource URL.
HTTP Status Code 302: Indicates a temporary redirect to the browser.
Different Scope: Request attributes set in the initial servlet are not carried over to the redirected servlet because a new request is created.

Recommended Related Tutorials

Continue mastering Java Servlets with these related video guides from Ram N Java:

Click here to watch in Youtube : https://www.youtube.com/watch?v=oWD-x1dIDSc

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SendRedirectDemo Project Dir Structure

LoginServlet.java

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet
{

    private static final long serialVersionUID = 1L;

    public void init() throws ServletException
    {
        System.out.println("--------------------------------------");
        System.out.println(" Init method is called in "
                + this.getClass().getName());
        System.out.println("--------------------------------------");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        String userName = request.getParameter("username");
        String passWord = request.getParameter("password");

        if (userName.equalsIgnoreCase("ram") && passWord.equals("ram"))
        {
            response.sendRedirect("http://localhost:8080/SendRedirectDemo/welcome");
        }
        else
        {
            out.print("Sorry UserName or Password is Wrong!");
            RequestDispatcher requestDispatcher = request
                    .getRequestDispatcher("/index.html");
            requestDispatcher.include(request, response);
        }
    }

    public void destroy()
    {
        System.out.println("----------------------------------------");
        System.out.println(" destroy method is called in "
                + this.getClass().getName());
        System.out.println("-----------------------------------------");
    }
}

WelcomeServlet.java

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 WelcomeServlet extends HttpServlet
{

    private static final long serialVersionUID = 1L;

    public void init() throws ServletException
    {
        System.out.println("--------------------------------------");
        System.out.println(" Init method is called in "
                + this.getClass().getName());
        System.out.println("--------------------------------------");
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        out.print("Welcome");
    }

    public void destroy()
    {
        System.out.println("--------------------------------------");
        System.out.println(" destroy method is called in "
                + this.getClass().getName());
        System.out.println("--------------------------------------");
    }
}

web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xmlns="http://java.sun.com/xml/ns/javaee" 
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
 metadata-complete="true" version="3.0">
  
  <display-name>SendRedirectDemo</display-name>
  
  <description>
        This is a simple web application with a source code organization
        based on the recommendations of the Application Developer's Guide.
    </description>
 
  <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>LoginServlet</servlet-class>
  </servlet>
  
  <servlet>
    <servlet-name>WelcomeServlet</servlet-name>
    <servlet-class>WelcomeServlet</servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  
  <servlet-mapping>
    <servlet-name>WelcomeServlet</servlet-name>
    <url-pattern>/welcome</url-pattern>
  </servlet-mapping>
  
</web-app>

index.html

<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>RequestDispatcherDemo</title>
</head>
<body>
    <form action="login" method="post">
        
        UserName :  <input type="text" name="username" /><br /> 
        
        Password :&nbsp; &nbsp; <input type="password" name="password" /><br /> 
            
        <input type="submit" value="login" />
        
    </form>
</body>
</html>

Environment Used

JDK version :1.6.0_30
Tomcat version : 7.0.50

To Download SendRedirectDemoApp Project Click the below link

https://sites.google.com/site/javaee4321/servlets/SendRedirectDemoApp.zip?attredirects=0&d=1

See also:

Servlets Tutorial

All Design Patterns Links