GenericServlet class in java

GenericServlet class:

GenericServlet class implements the Servlet and ServletConfig interfaces. GenericServlet is protocol-independent. It not provides the implementation of service method.

public abstract class GenericServlet implements Servlet, ServletConfig

GenericServlet class is in javax.servlet package (javax.servlet.GenericServlet).

Methods of GenericServlet class:

1. init(ServletConfig config): It is used to initialize the servlet. This method is called only once by the web container when it loads the servlet.
Syntax:

public void init(ServletConfig config)throws ServletException

2. service(ServletRequest request,ServletResponse response): It is used to respond to a request. It is called for every new request by web container.
Syntax:

public abstract void service(ServletRequest req,ServletResponse res)
throws ServletException, IOException

3. destroy(): It is used to destroy the servlet. This method is called only once by the web container when all threads of the servlet have exited or in a timeout case.
Syntax:

public void destroy()

4. getServletConfig(): It returns a servlet config object. This config object is passed in init method. Servlet config object contains initialization parameters and startup configuration for this servlet.
Syntax:

public ServletConfig getServletConfig()

5. getServletInfo(): It returns a string of information about servlet’s author, version, and copyright etc.
Syntax:

public String getServletInfo()

6. Init(): It is a convenience method which can be overridden so that there is no need to call super.init(config).
Syntax:

public void init() throws ServletException

7. getServletContext():It returns the ServletContext object in which this servlet is running.
Syntax:

public ServletContext getServletContext()

8. getInitParameter(String name): It returns the value for given parameter name. It returns null if parameter not exist.
Syntax:

public String getInitParameter(String name)

9. getInitParameterNames(): It returns the names of the servlet’s initialization parameters defined in web.xml file.
Syntax:

public Enumeration getInitParameterNames()

10. getServletName(): It returns the name of this servlet object.
Syntax:

public String getServletName()

11. log(String msg): This method writes the specified message to the servlet log file.
Syntax:

public void log(String msg)

12. log(String msg,Throwable t): This method writes an explanatory message and a stack trace for a given exception to the servlet log file.
Syntax:

public void log(String msg,Throwable t)

Servlet “Hello World” example by extending GenericServlet class.

HelloWorld.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
 
/**
 * This servlet program is used to print "Hello World" on 
 * client browser using GenericServlet class.
 * @author w3spoint
 */
public class HelloWorld extends GenericServlet {
    private static final long serialVersionUID = 1L;
 
    //no-argument constructor.
    public HelloWorld() {
 
    }
 
    @Override
    public void service(ServletRequest request, ServletResponse response)
			throws ServletException, IOException {
	response.setContentType("text/html");
	PrintWriter out = response.getWriter();
 
        out.println("<h1>Hello World example using" +
	    		" GenericServlet class.</h1>");
        out.close();		
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" 
xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
	<servlet>
		<servlet-name>HelloWorld</servlet-name>
		<servlet-class>
		   com.w3spoint.business.HelloWorld
		</servlet-class>
	</servlet>
 
	<servlet-mapping>
		<servlet-name>HelloWorld</servlet-name>
		<url-pattern>/HelloWorld</url-pattern>
	</servlet-mapping>
 
</web-app>

Output:

servlet example 2

Download this example.

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