User tracking
This is a process to keep information about users in multiple pages. Whenever a user gives information to a servlet then the destination servlet can
find values from the request by using the getParameter() method. When the user
provides a new request then the values avalable in the previous request get
lost, this is the nature of a stateless protocol. HTTP is a stateless protocol. User
tracking helps to keep information about users even if the request gets
changed. This can be done is four different ways given below:
- URL rewritting
- Hidden field
- Cookie
- Session
First we will discuss URL rewritting
this is a process to create an explict querystring with the help of a
hyperlink. The href attribute of <a> tag can contain a path of the destination with
the querystring. Whenever a user clicks on hyperlink then the destination servlet can
fetch values by using the getParameter() method of the request.
Example: In the first file 1 to 100 numbers will be displayed when a user clicks the number another page will appear showing that number the user had clicked previously.
First.java file
import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
public class first extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse res)throws
ServletException,IOException
{
PrintWriter out=res.getWriter();
out.println("<h2>");
for(int i=1;i<101;i++)
out.println("<a href='./second?x="+i+"'>"+i+"</a> " );
}
}
Second.java file
import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
public class second extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse res)throws
ServletException,IOException
{
PrintWriter out=res.getWriter();
String s=req.getParameter("x");
out.println("<html><body>");
out.println("<h1>"+"You clicked:"+s+"</h1>");
out.println("</body></html>");
}
}
Web.xml settings
<?xml version="1.0" encoding="ISO-8859-1"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one or more contributor
license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and limitations
under the License.
-->
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
<servlet>
<servlet-name>first</servlet-name>
<servlet-class>first</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>first</servlet-name>
<url-pattern>/first</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>second</servlet-name>
<servlet-class>second</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>second</servlet-name>
<url-pattern>/second</url-pattern>
</servlet-mapping>
</web-app>
Compile both the files as below
javac -cp servlet-api.jar first.java (for tomcat 6.0)
javac -cp servlet-api.jar second.java (for tomcat 6.0)
![User tracking Servlet]()
Output
Run the tomcat then write the below line in the URL
Here test is the Context path, which we mentioned in the server.xml file, which
is present in (E:\Program Files\Apache Software Foundation\Tomcat 6.0\conf)
directory.
http://localhost:8081/test/first
![User tracking Servlet]()
Remaining three will be discussed soon.
Thanks for reading