O: Using Servlets to retrieve HTTP data from browser

In the below post, we will examine how servlets can be used to retrieve information from the client browser.

ParameterServlet.java

package httpreqresp;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;

public class ParameterServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) 
              throws ServletException, IOException {
                 doPost (request, response);
   }
	public void doPost (HttpServletRequest request, HttpServletResponse response) 
		throws ServletException, IOException {
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.println("<html>");
		out.println("<head>");
		out.println("<title>Parameter Servlet</title>");
		out.println("</head>");
		out.println("<body>");
		Enumeration parameters = request.getParameterNames();
		String param = null;
		while (parameters.hasMoreElements()) {
			 param = (String) parameters.nextElements();
			 out.println (param + " : " + request.getParameter(param) + "<BR>");
		}
	 out.println("</body><//html>");
	  out.close();
	}
}

Form.html

<HTML>
<HEAD>
<TITLE>
Parameter Servlet Form
</TITLE>
</HEAD>

<BODY>

<form action="parameter" method="POST">
    <table width="400" border="0" cellspacing="0">
    <tr>
        <td>Name : </td>
        <td>
           <input type="text" name="name" size="20" maxlength="20">
        </td>
        <td> SSN: </td>
       <td>
            <input type="text" name="ssn" size="11" maxlength="11">
        </td>
        <tr>
            <td>Age: </td>
            <td>
                <input type="text" name="age" size="3" maxlength="3">
            </td>
            <td>email :</td>
            <td><input type="text" name="email" size="30" maxlength="30"></td>
        </tr>
        <tr>
         <td> &nbsp;</td>       
         <td> &nbsp;</td>
          <td> &nbsp;</td>
        <td>
           <input type="submit" name="Submit" value="Submit">
           <input type="reset" name="Reset" value="Reset"> 
        </td>
    </tr>
   </table>
</FORM>
<//BODY>
</HTML>

web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
  PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
  "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">
<web-app>
   <servlet>
		<servlet-name>ParameterServlet</servlet-name>
		<servlet-class>httpreqresp.ParameterServlet</servlet-class>
   </servlet>
   <servlet-mapping>
		<servlet-name>ParameterServlet</servlet-name>
		<url-pattern>parameter</url-pattern>
   </servlet-mapping>   
</web-app>

Directory	Contains
/httpreqresp	The root directory of the web application. All JSP and HTML files are stored here
/httpreqresp/WEB-INF	This directory contains all resources related to the application that are not in the document root of the application. It is where the web application deployment descriptor web.xml is located.
/httpreqresp/WEB-INF/classes	This is where the servlet and other classes are located.
/httpreqresp/WEB-INF/lib	This directory contains Java Archive (JAR) files that the web application is dependent on
/httpreqresp/src	The directory having the java source code.

Working of the Servlet to retrieve HTTP data.

Invoke

http://localhost:8080/httpreqresp/Form.html

After filling the required information press the SUBMIT button.

On SUBMIT button, the request is passed to the web container with url-pattern "parameter" (the action value for POST event), which checks in the web.xml file under web application /httpreqresp/WEB-INF folder and gets the corresponding servlet ParameterServlet, where the doGet method of the HttpServlet gets invoked which passes the request to doPost.

Here three methods can be used to retrieve request parameters from the web browser client.

public String ServletRequest.getParameter (String name);

public String[] ServletRequest.getParameterValues (String name);
public EnumerationServletRequest.getParameterNames ();

getParameter() method can be used when the request has only one parameter.
If the request has multiple parameter values, you should use getParameterValues method. getParameterValues returns the values of the specified parameters as an array of java.lang.Strings.
As the name suggests, getParameterNames returns the parameter names contained in the request as an Enumeration of strings or an empty enumeration if there are no parameters.

We now compile and deploy this code on the tomcat web server under webapps as follows. If you are using another web server like JBOSS, the deployment folder will be different, and accordingly the deployment directory will change.

We create a new folder httpreqresp under the webapps folder.

We place the .java file in the folder /httpreqresp/src folder as below

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp\src\ParameterServlet.java

We place the jsp file in the /httpreqresp folder as below

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp\Form.html

We place the web.xml file in the /httpreqresp/WEB-INF folder as below

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp\WEB-INF\web.xml

We compile the code using ant. We download a suitable version of ant and unzip it into a suitable folder path.

For the build we need to tell the ant build cmd a few important path variables

CLASSPATH

ANT_HOME

JAVA_HOME

PATH

In CLASSPATH I need to set the path for servlet-api.jar

set CLASSPATH=E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\lib\servlet-api.jar;

Set the path for ANT_HOME

set ANT_HOME=E:\install\ant\apache-ant-1.7.1-bin\apache-ant-1.7.1

Set the path for JAVA_HOME

set JAVA_HOME=E:\install\jdk

In the PATH variable I set the path for ANT_HOME/bin and JAVA_HOME/bin

set PATH=C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;E:\install\jdk\jdk\bin;E:\install\ant\apache-ant-1.7.1-bin\apache-ant-1.7.1\bin

I can put all the path variables in a bat file and run the bat file on cmd prompt.

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp>set_path

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp>set CLASSPATH=E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\lib\servlet-api.jar;

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp>set ANT_HOME=E:\install\ant\apache-ant-1.7.1-bin\apache-ant-1.7.1

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp>set JAVA_HOME=E:\install\jdk

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp>set PATH=E:\install\21cXE\dbhomeXE\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Program Files\PuTTY\;E:\install\jdk\jdk\bin;C:\Program Files (x86)\MySQL\MySQL Server 6.0\bin;E:\install\jdk\bin;C:\Users\winni\AppData\Local\Microsoft\WindowsApps;E:\install\ant\apache-ant-1.7.1-bin\apache-ant-1.7.1\bin

Once the various path variables are set, I create the ant build file and run the ant command.

A sample ant build file to compile my java code is below.

 <project name="httpreqresp" default="all" basedir=".">  
 <property name="struts.home"          value="E:\winnith\java\struts\home"/>  
 <property name="miscjar.home"       value="E:\winnith\java\project\strutsapp"/>  
 <property name="CATALINA_HOME" value="E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0"/>  
 <property name="tomcat.home" value="${CATALINA_HOME}"/>  
 <property name="src.dir" value="${basedir}/src"/>  
 <property name="build.dir" value="${basedir}/WEB-INF/classes"/>  
      <path id="compile.class.path">  
           <fileset dir="${tomcat.home}\lib">  
                <include name="*.jar"/>  
           </fileset>       
           <fileset dir="${struts.home}">  
                <include name="*.jar"/>  
           </fileset>  
           <fileset dir="${miscjar.home}">  
                <include name="*.jar"/>  
           </fileset>  
      </path>       
      <target name="all" depends="clean,compile"/>  
      <target name="compile" depends="clean">  
   <mkdir dir="${build.dir}"/>  
   <javac srcdir="${src.dir}" destdir="${build.dir}"/>  
  </target>  
      <target name="clean">  
           <delete dir="${build.dir}"/>  
      </target>  
 </project>

I now run the ant command as below

E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp>ant
Buildfile: build.xml

clean:
   [delete] Deleting directory E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp\WEB-INF\classes

compile:
    [mkdir] Created dir: E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp\WEB-INF\classes
    [javac] Compiling 1 source file to E:\install\apache-tomcat-6.0.0\apache-tomcat-6.0.0\webapps\httpreqresp\WEB-INF\classes

all:

BUILD SUCCESSFUL
Total time: 0 seconds

Now run

http://localhost:8080/httpreqresp/Form.html

request

response

References

Professional Jakarta Struts by James Goodwill, Richard Hightower

God's Word for the day

I have fought the good fight, I have kept the faith.

From now on, there is reserved for me the crown of righteousness,

which the Lord, the righteous judge, will give me on that day,

and not only to me but also to all who have longed for his appearing.

2 Timothy 4:7-8

Salt and Light

You are the light of the world.

A city built on a high hill cannot be hid.

No one after lighting a lamp puts it under the bushel basket,

But on the lampstand, and it gives light to all in the house.

In the same way, let your light shine before others,

so that they may see your good works,

And give glory to your Father in Heaven.

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Thursday, September 11, 2025

Using Servlets to retrieve HTTP data from browser

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