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HttpServlet

Jakob Jenkov
Last update: 2014-05-25

The javax.servlet.http.HttpServlet class is a slightly more advanced base class than the GenericServlet shown in the Simple Servlet example.

The HttpServlet class reads the HTTP request, and determines if the request is an HTTP GET, POST, PUT, DELETE, HEAD etc. and calls one the corresponding method.

To respond to e.g. HTTP GET requests only, you will extend the HttpServlet class, and override the doGet() method only. Here is an example:

public class SimpleHttpServlet extends HttpServlet {

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

      response.getWriter().write("<html><body>GET response</body></html>");
  }
}

The HttpServlet class has methods you can override for each HTTP method (GET, POST etc.). Here is a list of the methods you can override:

  • doGet()
  • doPost()
  • doHead()
  • doPut()
  • doDelete()
  • doOptions()
  • doTrace()

Most often you just want to respond to either HTTP GET or POST requests, so you just override these two methods.

If you want to handle both GET and POST request from a given servlet, you can override both methods, and have one call the other. Here is how:

public class SimpleHttpServlet extends HttpServlet {

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

      doPost(request, response);
  }

  protected void doPost( HttpServletRequest request,
                         HttpServletResponse response)
        throws ServletException, IOException {

      response.getWriter().write("GET/POST response");
    }
}

I would recommend you to use the HttpServlet instead of the GenericServlet whenever possible. HttpServlet is easier to work with, and has more convenience methods than GenericServlet.

Jakob Jenkov




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