Servlet Chaining:

Servlet Chaining:

If a client request is processed by group of servlets, then that servlets are known as servlet chaining or if the group of servlets process a single client request then those servlets are known as servlet chaining.

In order to process a client request by many number of servlets then we have two models, they are forward model and include model.

Forward model:

In this model when we forward a request to a group of servlets, finally we get the result of destination servlet as a response but not the result of intermediate servlets.

Include model:

If a single client request is passed to a servlet and that servlet makes use of other group of servlets to process a request by including the group of servlets into a single servlet.

Note: One servlet can include any number of servlets where as one servlet can forward to only one servlet at a time.

FirstServlet.java

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class FirstServlet extends HttpServlet {

    public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

        res.setContentType("text/html");

        PrintWriter pw = res.getWriter();

        pw.println("<h2>I AM FROM FirstServlet BEGINNING</h2>");

        ServletContext ctx = getServletContext();

        RequestDispatcher rd = ctx.getRequestDispatcher("/SS");

        rd.include(req, res);

        pw.println("<h2>I AM FROM FirstServlet ENDING</h2>");

    }

};

SecondServlet.java

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class SecondServlet extends HttpServlet {

    public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

        res.setContentType("text/html");

        PrintWriter pw = res.getWriter();

        pw.println("<h2>I AM FROM SecondServlet</h2>");

    }

};

Update web.xml with

<servlet>

    <servlet-name>FS</servlet-name>

    <servlet-class>FirstServlet</servlet-class>

  </servlet>

  <servlet-mapping>

    <servlet-name>FS</servlet-name>

    <url-pattern>/FS</url-pattern>

  </servlet-mapping>

<servlet>

    <servlet-name>SS</servlet-name>

    <servlet-class>SecondServlet</servlet-class>

  </servlet>

  <servlet-mapping>

    <servlet-name>SS</servlet-name>

    <url-pattern>/SS</url-pattern>

  </servlet-mapping>

Output: