Difference between GenericServlet and HttpServlet

GenericServlet class implements Servlet, ServletConfig and Serializable interfaces. It provides the implementaion of all the methods of these interfaces except the service method. GenericServlet may be directly extended by a servlet, although it’s more common to extend a protocol-specific subclass such as HttpServlet.

GenericServlet makes writing servlets easier. It provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface. GenericServlet also implements the log method, declared in the ServletContext interface.

GenericServlet class can handle any type of request so it is protocol-independent.

You may create a generic servlet by inheriting the GenericServlet class and providing the implementation of the service method.

Methods of GenericServlet class
There are many methods in GenericServlet class. They are as follows:

  • public void init(ServletConfig config) is used to initialize the servlet.
  • public abstract void service(ServletRequest request, ServletResponse response) provides service for the incoming request. It is invoked at each time when user requests for a servlet.
  • public void destroy() is invoked only once throughout the life cycle and indicates that servlet is being destroyed.
  • public ServletConfig getServletConfig() returns the object of ServletConfig.
  • public String getServletInfo() returns information about servlet such as writer, copyright, version etc.
  • public void init() it is a convenient method for the servlet programmers, now there is no need to call super.init(config)
  • public ServletContext getServletContext() returns the object of ServletContext.
  • public String getInitParameter(String name) returns the parameter value for the given parameter name.
  • public Enumeration getInitParameterNames() returns all the parameters defined in the web.xml file.
  • public String getServletName() returns the name of the servlet object.
  • public void log(String msg) writes the given message in the servlet log file.
  • public void log(String msg,Throwable t) writes the explanatory message in the servlet log file and a stack trace.

Difference between HttpServlet and GenericServlet
Signature: public abstract class GenericServlet extends java.lang.Object implements Servlet, ServletConfig, java.io.Serializable

  • GenericServlet defines a generic, protocol-independent servlet.
  • GenericServlet gives a blueprint and makes writing servlet easier.
  • GenericServlet provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface.
  • GenericServlet implements the log method, declared in the ServletContext interface.
  • To write a generic servlet, it is sufficient to override the abstract service method.

Signature: public abstract class HttpServlet extends GenericServlet implements java.io.Serializable

  • HttpServlet defines a HTTP protocol specific servlet.
  • HttpServlet gives a blueprint for Http servlet and makes writing them easier.
  • HttpServlet extends the GenericServlet and hence inherits the properties GenericServlet.

Servlet Example by inheriting the GenericServlet class-

Let’s see the simple example of servlet by inheriting the GenericServlet class.

import java.io.*;  
    import javax.servlet.*;  
    public class HelloServlet extends GenericServlet{  
    public void service(ServletRequest req,ServletResponse res)  
    throws IOException,ServletException{  
    PrintWriter out=res.getWriter();  
    out.print("<b>hello generic servlet</b>");  

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