Tuesday, May 1, 2012

Step by step guide to implement Hello world servlet

In this example we will see how to do coding, compiling, deploying, and running a simple Hello World servlet which will just print "Hello World" in the browser.

To learn life cycle of servlet, click here

We will useTomcat server to run our HelloWorld servlet. To download tomcat, click here

Lets create our project folder in webapps lets say TestServlet

Example:
C:\apache-tomcat-7.0.11\webapps\TestServlet

Now lets create our first hello world servlet, lets say HelloWorldServlet.java

HelloWorldServlet.java

C:\apache-tomcat-7.0.11\webapps\TestServlet\WEB-INF\classes\HelloWorldServlet.java
/* HelloWorldServlet.java */

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloWorldServlet extends HttpServlet {
 
 public void doGet(HttpServletRequest request, HttpServletResponse response) {
  doPost(request,response);
 }
 
 public void doPost(HttpServletRequest request, HttpServletResponse response) {
  PrintWriter pw = null;
  try {
   pw = response.getWriter();
  } catch (IOException e) {
   e.printStackTrace();
  }
  pw.println("<html>");
  pw.println("<body>");
  pw.println("<h2>Hello World!!</h2>");
  pw.println("</body>");
  pw.println("</html>");
 }

}


Compilation of HelloWorldServlet.java

As you can see HelloWorldServlet extends HttpServlet, hence it needs to import package javax.servlet.http. In tomcat it is provided as a part of servlet-api.jar file. Which is in the directory C:\apache-tomcat-7.0.11\lib. To compile our class just include the said jar file in classpath.

Example:

$javac -cp C:\apache-tomcat-7.0.11\lib\servlet-api.jar HelloWorldServlet.java

You should see HelloWorldServlet.class file generated in the same folder.

web.xml
C:\apache-tomcat-7.0.11\webapps\TestServlet\WEB-INF\web.xml

web.xml file (also known as the deployment descriptor). This file is the heart of a web application, and every web application must have it. It contains the information needed by the servlet container in order to run the web application, such as servlet declarations and mappings, properties, authorization and security constraints, and so forth.
<?xml version="1.0" encoding="UTF-8"?>
<web-app> 
  <servlet>
  <servlet-name>HWServletName</servlet-name>
  <servlet-class>HelloWorldServlet</servlet-class>
 </servlet>
 <servlet-mapping>
  <servlet-name>HWServletName</servlet-name>
  <url-pattern>/hwservlet</url-pattern>
 </servlet-mapping>
</web-app>


After adding the file web.xml, restart your tomcat server. Run below mentioned file to start tomcat server.

Windows
C:\apache-tomcat-7.0.11\bin\startup.bat

Linux
C:\apache-tomcat-7.0.11\bin\startup.sh

Now we are done, open browser and hit below mentioned URL.

http://localhost:8080/TestServlet/hwservlet

Output


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