JAVA EE: sendRedirect

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Tuesday, 6 May 2014

Servlets : Page Redirection

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What is Page Redirection in Java Servlets?

In web applications, page redirection occurs when a server tells a web browser to go visit a completely different URL instead of returning page content immediately. In Java Servlets, redirection is typically performed using the sendRedirect() method of HttpServletResponse.

When a servlet initiates a redirect, it sends back an HTTP response containing a redirect status code (typically 302 Found) along with a Location response header specifying the new target URL. The browser automatically recognizes this header and sends a brand new GET request to that destination.

How Client-Side Redirection Works (Two Request-Response Cycles)

Understanding the exact workflow is key to using redirection correctly:

Request 1: The client browser sends a request to ServletA.
Response 1: ServletA executes response.sendRedirect("newPage"). The server issues a 302 HTTP status code and attaches the new destination URL in the header.
Request 2: The client's browser reads the header, changes the URL in the address bar, and automatically triggers a fresh GET request to newPage.
Response 2: The destination server processes Request 2 and sends back the final web page content.

Basic Syntax & Practical Code Examples

You can redirect users to another internal resource inside the same web application, or to an external third-party domain:

    // 1. Relative Redirection within the same application

    response.sendRedirect("welcome.html");

    // 2. Relative Redirection to another servlet

    response.sendRedirect("DashboardServlet");

    // 3. Absolute Redirection to an external website

    response.sendRedirect("https://www.google.com");

Page Redirection (sendRedirect) vs Request Forward (forward)

URL Bar Update: sendRedirect() always updates the URL displayed in the client's browser, whereas RequestDispatcher.forward() keeps the original URL hidden.
Request Scope: Because redirection triggers a brand-new HTTP request, original request attributes are lost. Forwarding preserves the original request and response objects.
Scope of Target: sendRedirect() can direct the user to resources outside the current web application and external domains. Forwarding only works within the same web container.

When Should You Use Page Redirection?

Post/Redirect/Get (PRG) Pattern: Preventing accidental form re-submissions (e.g., duplicate payments or duplicate database inserts) when a user refreshes the page.
Authentication Flow: Redirecting unauthenticated visitors to a login page, and then redirecting them back to a dashboard upon successful login.
External Navigation: Directing visitors to external partner websites or third-party payment gateways.

📺 Related Redirection & Navigation Tutorials

Continue mastering navigation and request flow in Servlets with these channel tutorials:

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

Click the below Image to Enlarge

PageRedirection Project Dir Structure

PageRedirectServlet.java

import java.io.IOException;

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

public class PageRedirectServlet 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
    {
        // Set response content type
        response.setContentType("text/html");

        // New location to be redirected
        String site = new String("http://www.google.com");

        response.setStatus(response.SC_MOVED_TEMPORARILY);
        response.setHeader("Location", site);
    }

    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>PageRedirection</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>PageRedirect</servlet-name>
    <servlet-class>PageRedirectServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>PageRedirect</servlet-name>
    <url-pattern>/PageRedirect</url-pattern>
  </servlet-mapping>

</web-app>

index.html

<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>PageRedirectDemo</title>
</head>
<body>
    <li><a href="PageRedirect">PageRedirect</a></li>
</body>
</html>

Environment Used

JDK version :1.6.0_30
Tomcat version : 7.0.50

To Download PageAutoRefreshApp Project Click the below link

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

See also:

Servlets Tutorial

All Design Patterns Links

Monday, 5 May 2014

Servlets : Send Redirect Demo[Transfer control to different domain]

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What is response.sendRedirect() in Java Servlets?

In Java Servlet programming, HttpServletResponse.sendRedirect(String location) is used to redirect an incoming client request to an entirely different resource.

Unlike RequestDispatcher.forward()—which operates purely server-side within the same web application—sendRedirect() instructs the client's browser to make a fresh request to a new URL. This means you can transfer control not only within the same container, but also across external domains (such as Google, Yahoo, or external payment gateways).

How sendRedirect Works Under the Hood

The client sends an HTTP request to your servlet endpoint (e.g., /search).
The servlet processes incoming parameters and invokes response.sendRedirect("https://www.google.com/search?q=" + query).
The servlet container returns an HTTP status code 302 (Found / Temporary Redirect) with the Location header containing the target URL.
The client's browser reads this header and automatically issues a brand-new GET request to the target domain.
The user's browser address bar updates to reflect the new target URL.

Step-by-Step Implementation: Search Query Redirect

Let us look at a practical demonstration where search text entered in an HTML form is redirected to an external search engine:

1. The HTML Input Form (index.html)

<form action="searchRedirect" method="GET">
  <label for="search">Search Query:</label>
  <input type="text" id="search" name="query" />
  <input type="submit" value="Search on Google" />
</form>

2. The Redirect Servlet (SearchRedirectServlet.java)

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SearchRedirectServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        // Retrieve search query submitted from form
        String query = req.getParameter("query");

        // Redirect control to an external domain
        if (query != null && !query.trim().isEmpty()) {
            res.sendRedirect("https://www.google.com/search?q=" + query);
        } else {
            res.sendRedirect("https://www.google.com");
        }
    }
}

Key Differences: sendRedirect() vs RequestDispatcher.forward()

Scope: sendRedirect() can redirect to any external domain, whereas forward() works only within the same web application.
Browser Address Bar: In sendRedirect(), the browser URL updates to the new location. In forward(), the browser URL remains unchanged.
HTTP Requests: sendRedirect() involves two separate request/response round-trips; forward() executes entirely within a single round-trip.

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

Click the below Image to Enlarge

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