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Saturday, 9 August 2014

Servlets : URL Rewriting Demo

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What is URL Rewriting in Java Servlets?

HTTP is an inherently stateless protocol, which means the server does not remember user data between multiple web requests. URL Rewriting is a fundamental session tracking mechanism where extra session information (such as a session ID or custom parameter) is appended directly to the end of a hyperlink URL as a query parameter (e.g., targetURL?paramName=value).

Unlike browser cookies, URL rewriting does not require cookie support and functions seamlessly even when cookies are disabled on the client machine.

Step 1: Create the User Input Page (index.html)

Start by creating an HTML form that collects the initial data from the client and submits it to your first servlet:

<form action="FirstServlet" method="post">
  Enter User Name: <input type="text" name="userName" /><br><br>
  <input type="submit" value="Proceed" />
</form>

Step 2: Rewrite the URL in the First Servlet (FirstServlet.java)

In the first servlet, read the parameter from the request and dynamically construct a hyperlink containing the user data appended in the query string:

String userName = request.getParameter("userName");

PrintWriter out = response.getWriter();
out.println("<h2>Hello, " + userName + "!</h2>");
out.println("<p>Click the link below to continue:</p>");
out.println("<a href='SecondServlet?uname=" + userName + "'>Go to Second Servlet</a>");

Step 3: Retrieve the Data in the Target Servlet (SecondServlet.java)

When the user clicks the rewritten link, the target servlet extracts the appended query parameter via request.getParameter():

String userName = request.getParameter("uname");

PrintWriter out = response.getWriter();
out.println("<h2>Welcome to Second Servlet!</h2>");
out.println("<p>Retrieved User Name: <strong>" + userName + "</strong></p>");

Pros and Cons of URL Rewriting

  • Advantage: Works reliably across all browsers without depending on client cookie permissions.
  • Advantage: No server session memory footprint is required for simple parameter forwarding.
  • Limitation: Visible in the browser's address bar and history; sensitive information (like passwords) must never be sent this way.
  • Limitation: Only links and navigation generated with rewritten query strings will maintain the state.

📺 Related Session Tracking Tutorials

Expand your understanding of session management in Servlets with these tutorials:

Click here to watch in Youtube : https://www.youtube.com/watch?v=0Ch2Bfea5yw

Click the below Image to Enlarge
Servlets : URL Rewriting Demo
Servlets : URL Rewriting Demo
FirstServlet.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 FirstServlet 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();

        String userName = request.getParameter("userName");
        out.print("Welcome " + userName);

        // appending the username in the query string
        out.print("<a href='servlet2?uname=" + userName +"'> :  visit</a>");

        out.close();
    }

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

}
SecondServlet.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 SecondServlet 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();

        // getting value from the query string
        String userName = request.getParameter("uname");
        out.print("Hello " + userName);

        out.close();

    }

    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>URLRewritingDemo</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>s1</servlet-name>
        <servlet-class>FirstServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>s2</servlet-name>
        <servlet-class>SecondServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>s1</servlet-name>
        <url-pattern>/servlet1</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>s2</servlet-name>
        <url-pattern>/servlet2</url-pattern>
    </servlet-mapping>
</web-app>
index.html 
<html>
<body>
    <form action="servlet1">
        Name:<input type="text" name="userName" /><br /> 
        <input type="submit" value="go" />
    </form>
</body>
</html>

Environment Used 

JDK version :1.7.0_51
Tomcat version : 7.0.50 

To Download URLRewritingDemoApp Project Click the below link

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

See also:

  • Servlets Tutorial
  • All Design Patterns Links
  • JDBC Tutorial
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