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Servlets - Page Redirection and Hits Counter

Page Redirecting

Page redirection is a technique where the client is sent to a new location other than requested. Page redirection is generally used when a document moves to a new location or may be because of load balancing.
The simplest way of redirecting a request to another page is using method sendRedirect() of response object. Following is the signature of this method −
public void HttpServletResponse.sendRedirect(String location) 
throws IOException
This method sends back the response to the browser along with the status code and new page location. You can also use setStatus() and setHeader() methods together to achieve the same −
.... 
String site = "http://www.thenewpage.com" ; 
response.setStatus(response.SC_MOVED_TEMPORARILY); 
response.setHeader("Location", site);  
....

Example

This example shows how a servlet performs page redirection to another location −
import java.io.*;
import java.sql.Date;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class PageRedirect extends HttpServlet {
    
   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://http://www.squizspot.blogspot.com");

      response.setStatus(response.SC_MOVED_TEMPORARILY);
      response.setHeader("Location", site);    
   }
}
Now let us compile above servlet and create following entries in web.xml
....
<servlet>
   <servlet-name>PageRedirect</servlet-name>
   <servlet-class>PageRedirect</servlet-class>
</servlet>

<servlet-mapping>
   <servlet-name>PageRedirect</servlet-name>
   <url-pattern>/PageRedirect</url-pattern>
</servlet-mapping>
....
Now call this servlet using URL http://localhost:8080/PageRedirect. This would redirect you to URL http://www.squizspot.blogspot.com.

Hit Counter for a Web Page

Many times you would be interested in knowing total number of hits on a particular page of your website. It is very simple to count these hits using a servlet because the life cycle of a servlet is controlled by the container in which it runs.
Following are the steps to be taken to implement a simple page hit counter which is based on Servlet Life Cycle −
  • Initialize a global variable in init() method.
  • Increase global variable every time either doGet() or doPost() method is called.
  • If required, you can use a database table to store the value of global variable in destroy() method. This value can be read inside init() method when servlet would be initialized next time. This step is optional.
  • If you want to count only unique page hits with-in a session then you can use isNew() method to check if same page already have been hit with-in that session. This step is optional.
  • You can display value of the global counter to show total number of hits on your web site. This step is also optional.
Here I'm assuming that the web container will not be restarted. If it is restarted or servlet destroyed, the hit counter will be reset.

Example

This example shows how to implement a simple page hit counter −
import java.io.*;
import java.sql.Date;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class PageHitCounter extends HttpServlet {

   private int hitCount; 

   public void init() { 
      // Reset hit counter.
      hitCount = 0;
   } 

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

      // Set response content type
      response.setContentType("text/html");

      // This method executes whenever the servlet is hit 
      // increment hitCount 
      hitCount++; 
      PrintWriter out = response.getWriter();
      String title = "Total Number of Hits";
      String docType = "<!doctype html public \"-//w3c//dtd html 4.0 " + "transitional//en\">\n";
      
      out.println(docType +
         "<html>\n" +
            "<head><title>" + title + "</title></head>\n" +
            "<body bgcolor = \"#f0f0f0\">\n" +
               "<h1 align = \"center\">" + title + "</h1>\n" +
               "<h2 align = \"center\">" + hitCount + "</h2>\n" +
            "</body>
         </html>"
      );
   }
   
   public void destroy() { 
      // This is optional step but if you like you
      // can write hitCount value in your database.
   } 
}
Now let us compile above servlet and create following entries in web.xml
<servlet>
   <servlet-name>PageHitCounter</servlet-name>
   <servlet-class>PageHitCounter</servlet-class>
</servlet>

<servlet-mapping>
   <servlet-name>PageHitCounter</servlet-name>
   <url-pattern>/PageHitCounter</url-pattern>
</servlet-mapping>
....
Now call this servlet using URL http://localhost:8080/PageHitCounter. This would increase counter by one every time this page gets refreshed and it would display following result −

Total Number of Hits



6



Hit Counter for a Website:
Many times you would be interested in knowing total number of hits on your whole website. This is also very simple in Servlet and we can achieve this using filters.
Following are the steps to be taken to implement a simple website hit counter which is based on Filter Life Cycle −
  • Initialize a global variable in init() method of a filter.
  • Increase global variable every time doFilter method is called.
  • If required, you can use a database table to store the value of global variable in destroy() method of filter. This value can be read inside init() method when filter would be initialized next time. This step is optional.
Here I'm assuming that the web container will not be restarted. If it is restarted or servlet destroyed, the hit counter will be reset.

Example

This example shows how to implement a simple website hit counter −
// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

public class SiteHitCounter implements Filter {

   private int hitCount; 

   public void  init(FilterConfig config) throws ServletException {
      // Reset hit counter.
      hitCount = 0;
   }

   public void  doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 
      throws java.io.IOException, ServletException {

      // increase counter by one
      hitCount++;

      // Print the counter.
      System.out.println("Site visits count :"+ hitCount );

      // Pass request back down the filter chain
      chain.doFilter(request,response);
   }
   
   public void destroy() { 
      // This is optional step but if you like you
      // can write hitCount value in your database.
   } 
}
Now let us compile the above servlet and create the following entries in web.xml
....
<filter>
   <filter-name>SiteHitCounter</filter-name>
   <filter-class>SiteHitCounter</filter-class>
</filter>

<filter-mapping>
   <filter-name>SiteHitCounter</filter-name>
   <url-pattern>/*</url-pattern>
</filter-mapping>
....
Now call any URL like URL http://localhost:8080/. This would increase counter by one every time any page gets a hit and it would display following message in the log −
Site visits count : 1
Site visits count : 2
Site visits count : 3
Site visits count : 4
Site visits count : 5
..................

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