How to write, compile and execute JAVA servlets

Servlets are core java programs that can be executed on the webserver upon the request via the url.

Prerequests for running a java servlet:

1. install JRE (Java Runtime Environment)

1.1 Download the JRE installation pack. Click here to download
1.2 Install the pack as per instructions.
1.3 Set the Environment Variable, JRE_HOME to the installed location.

1.3.1 Steps to set the Environment Variable in Windows XP/Vista
1.3.1.1 MyComputer-> Properties -> ADVANCED tab .
1.3.1.2 Click the "Environment Variables" button.
1.3.1.3 Add a new System Variable:
Variable name: JRE_HOME
Variable value: C:\Program Files\Java\jre1.5.0_01\
(or ur insalled location)

1.4 You have done with installing JRE


2. Install apache-tomcat.

2.1 Download a binary distribution of Tomcat from: http://tomcat.apache.org
2.2 Unpack the binary distribution into a convenient location so that the distribution resides in its own directory (conventionally named "apache-tomcat-[version]").


3. Include the servlet-api.jar to the CLASSPATH environment varialbe.
servlet-api.jar is not contained in JDK. It comes along with the apache-tomcat server. It is located "lib" folder of Tomcat installation direcotry.

eg: set classpath=C:\apache-tomcat-6.0.14\lib\servlet-api.jar;%classpath%

4. Start the ApacheTomcat server(startup.bat inside bin folder).

5. Now your server is ready and running.


Writing a Sample Java Servlet ::

Java servlets are no different from normal java programs. The servlet file is of .java extension. It uses javax.servlet package.

A sample and simple java servlet example :

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

public class myExample extends HttpServlet {

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

response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("< HTML > \n" +
"< HEAD > < TITLE > Servlet Example from My-Tech-Experiments.blogspot.com </TITLE > < /HEAD >\n" +
"< BODY >\n" );

out.println( "<H1> Servlet Example < /H1 >\n" + " A simple Servlet.. <br/><br/><br/>Thought for the day: You never get a second chance to make the first impression.
</BODY></HTML >");
}

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

}

How to run the servlet :

step 1: Compile the servletName.java file using javac compiler just like anyother java file is compiled.

Step 2: Move the .class file to $java_installation_directory\webapps\ROOT\WEB-INF\classes\
If any directory is not found in the path, create it.

Step 3: Open the web.xml file in $java_installation_directory\webapps\ROOT\WEB-INF\
if it does not exist, create it. We use this file to map the servlet. It is must

Step 4: its content should look like this:

< ?xml version="1.0" encoding="ISO-8859-1"? >

<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">

 <display-name >Welcome to Tomcat </display-name >

<description >

     Welcome to Tomcat

</description >

<servlet >

<servlet-name >HelloWWW </servlet-name >

<servlet-class >HelloWWW </servlet-class >

</servlet >

<servlet-mapping >

<servlet-name >HelloWWW </servlet-name >

<url-pattern >/servlet/HelloWWW </url-pattern >

</servlet-mapping >

</web-app >

Step 5: Run the servlet using the browser. Type http://localhost:8080/servlet/myExample in the adress bar.

Step 6: Enjooyyy...>!!!!


Note: You can use servlets to receive form-data as POST and GET. Do a google search on it and you will find it. Feeling too lazy to write that too here... check back late.. i might have posted it.