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EXAMPLE OF KEEPALIVE CONNECTION


package sunexamples;

import java.io.*;

import javax.servlet.*;
import javax.servlet.http.*;

/**
 * This is an example of different ways to do keepalive connections
 * with servlets. The Content-Length header needs to be set for
 * keep-alive to work.  This is done automatically for servlets with
 * small amounts of output (<4K), but needs to be done manually
 * otherwise.
 * <P>
 * <B>What is keep-alive, and why should you care?</B><BR>
 * <P>
 * When a browser talks to a server, it needs to establish a TCP connection.
 * Establishing this connection is expensive in terms of time.  Keep-Alive
 * connections are connections which keep the connection open for subsequent
 * requests, greatly speeding the downloading of data from the server.
 * By ensuring that you follow the simple rules illustrated below, you
 * can enable automatic establishment of Keep-Alive connections from your
 * servlet.
 *
 * @author Jim Driscoll
 * @version 1.3 01/27/99
 *
 */

public class KeepAliveServlet extends HttpServlet {

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

        res.setContentType("text/html");
        PrintWriter out = res.getWriter();

 //Set up the strings we will use for output
 String str1 = "<HTML><HEAD><TITLE> Keep-Alive Servlet Output";
 str1 = str1 + "</TITLE></HEAD><BODY>\r\n";
 String str2 = "<h1> Keep-Alive Servlet Output </h1>\r\n";
 String str3 = "<P>This is output from Keep-Alive Servlet.\r\n";
 String str4 = "</BODY></HTML>\r\n";
 int strlen1 = str1.length();
 int strlen2 = str2.length();
 int strlen3 = str3.length();
 int strlen4 = str4.length();

 String runType = req.getParameter("runType");
 if (runType == null ||runType.equals("short nohead")) {;
     // First the "normal" way - keepalive and content-length should
     // be automatically set
            out.print(str1);
     out.print(str2);
     out.print(str3);
     out.print(str4);
     out.close();
        } else if (runType.equals("short nohead flush")) {
     // If you have a flush() of the output stream,
     // content length can't be determined - so,
     // keepalive will not be enabled!  (Don't worry,
            // the output stream is flushed on close - you
     // won't lose any data)
            out.print(str1);
     out.print(str2);
     out.print(str3);
     out.flush();
     out.print(str4);
     out.close();
        } else if (runType.equals("long nohead")) {
            // This way tests a large body with no content-length specified
     // It will not, normally, have keepalive enabled
     // Note that the cut-off for automatic determination of
     // content-length is 4k bytes in JavaWebServer
            out.print(str1);
     out.print(str2);
     for (int i = 0; i < 100;i++) {
  out.println(str3);
     }
     out.print(str4);
     out.close();
 } else if (runType.equals("short head")) {
     // This way manually sets the content-length,
     // keepalive should be on automatically
     res.setContentLength(strlen1+strlen2+strlen3+strlen4);
            out.print(str1);
     out.print(str2);
     out.print(str3);
     out.print(str4);
     out.close();
 } else if (runType.equals("long head")) {
     // This way manually sets the content-length on long output,
     // which should cause keepalive to be enabled
     res.setContentLength(strlen1+strlen2+(strlen3*100)+strlen4);
            out.print(str1);
     out.print(str2);
     for (int i = 0; i < 100;i++) {
  out.print(str3);
     }
     out.print(str4);
     out.close();
 } else { //Bogus value
            out.println("<HTML><HEAD><TITLE> Keep-Alive Servlet Output </TITLE></HEAD><BODY>");
     out.println("<h1> Keep-Alive Servlet Output </h1>");
     out.println("<P>Bogus value set for querystring.");
     out.println("<P>Set the runType parameter to one of:.");
     out.println("short+nohead");
     out.println("short+head");
     out.println("long+nohead");
     out.println("long+head");
     out.println("</BODY></HTML>");
     out.close();
 }
    }

    public String getServletInfo() {
        return "A servlet which demonstrates keep-alive programming";
    }
}