Example on Servlet Life Cycle in Java

Let us see one example on servlet life cycle. Do you have any doubts related to the concept ? if so please check this Servlet Life Cycle theory article before you execute this example.

Files required

• ServletLifeCycle.java
• web.xml

Directory Structure

ServletLifeCycle.java

package java4s;

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

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

public class ServletLifeCycle extends HttpServlet
{

	public ServletLifeCycle()
	{	
		System.out.println("Am from default constructor");
	}

	public void init(ServletConfig config)
	{
		System.out.println("Am from Init method...!");
	}

	public void doGet(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException
	{	
		res.setContentType("text/html");
		PrintWriter pw = res.getWriter();
		pw.println("I am from doGet method");
		pw.close();
	}	

	public void destroy()
	{
		System.out.println("Am from Destroy methods");
	}

}

web.xml

<web-app>
      <servlet>
            <servlet-name>second</servlet-name>
            <servlet-class>java4s.ServletLifeCycle</servlet-class>
         <load-on-startup>1</load-on-startup>
      </servlet>

      <servlet-mapping>
            <servlet-name>second</servlet-name>
            <url-pattern>/lifecycle1</url-pattern>
      </servlet-mapping>
</web-app>

Execution Flow

• Right click on your project ‘root(project folder)’ > Run as > click on ‘Run on Server‘
• Then eclipse will open an internal web browser with URL  —  http://localhost:2013/Servlet-Life-CycleExample/
• Now just append our project folder name to that URL, so the final URL will be like http://localhost:2013/Servlet-Life-CycleExample/Servlet-Life-CycleExample
• Press enter, now you will be able to see the output

Flow

• When ever you hit the final URL (http://localhost:2013/Servlet-Life-CycleExample/Servlet-Life-CycleExample), servlet container will first loads web.xml and check the value in <url-pattern> tag [ line number 10, we have given the pattern name as /lifecycle1 ]
• Immediately it will check the value in <servlet-name> tag [line number 9, we have given second]
• Now it will search for the same value second in <servlet-name> under <servlet> tag [that’s what we have in line number 3 ]
• So value of <servlet-name> under <servlet-mapping> & <servlet> are same [in this case @ line numbers 9,3 ]
• If so container will load java class given in <servlet-class> tag [line number 4, our class name is java4s.ServletLifeCycle ]
• Finally servlet container came to ‘ServletLifeCycle‘ class, it will executes init() method first (only once) > then service() or doGet() or doPost() method [ in our case doGet() ]
• Finally destroy() method will be executed before our object get garbage collected.

Hope i explained properly, you understand right :-), i will explain <load-on-startup> later just forget as of now.

 Output

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• Example of ServletContext in Java
• Understanding ServletConfig and ServletContext
• Example on getParameterValues() method of Servlet Request
• Example on getParameterMap() method of Servlet Request Object
• Example on getParameterNames() method of Servlet Request Object

::. About the Author .::
		Sivateja Kandula - Java/J2EE Full Stack Developer Founder of Java4s - Get It Yourself, A popular Java/J2EE Programming Blog, Love Java and UI frameworks. You can sign-up for the Email Newsletter for your daily dose of Java tutorials.