import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import com.oreilly.servlet.ServletUtils;
public class ChatPage extends HttpServlet implements Runnable {
static final int MESSAGE_ARCHIVE_SIZE = 10; // save the last 10 messages
ChatServlet chat = null; // the servlet to reuse
String[] messages = new String[MESSAGE_ARCHIVE_SIZE]; // circular array
int messageIndex = 0; // index into the messages array
Thread update = null; // thread to update new messages
// Gets new messages from the chat servlet and inserts them in
// the messages circular array.
public void run() {
while (true) {
String message = chat.getNextMessage();
synchronized (this) {
messages[messageIndex] = message;
messageIndex = (messageIndex + 1) % MESSAGE_ARCHIVE_SIZE;
}
}
}
// Prints the message archive (the 10 latest messages) and a text
// field where the reader can input a new message.
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
// Turn off caching, so the latest messages are always displayed.
// (Works around a Netscape problem.)
res.setHeader("Pragma", "no-cache");
// For our first request, "chat" is null and needs to use
// ServletUtils.getServlet() to get the ChatServlet instance.
// Then we need to start another thread to listen for chat's
// new messages.
if (chat == null) {
chat = (ChatServlet)ServletUtils.getServlet(
"ChatServlet", req, getServletContext());
if (chat != null) {
update = new Thread(this);
update.start();
}
}
// Print a pretty header.
out.println("");
out.println("ChatPage");
out.println("Welcome to ChatPage!
");
// Print the message archive, oldest first.
// Synchronized so it doesn't change while we're printing it.
synchronized (this) {
out.println("Recent messages:");
int i = messageIndex;
do {
String message = messages[i];
if (message != null) out.println(message + "
");
i = (i + 1) % MESSAGE_ARCHIVE_SIZE;
} while (i != messageIndex);
}
// Print a button that gets new messages.
out.println("
");
// Print a form where the reader can submit a new message.
out.println("
");
out.println("");
// Print a pretty footer.
out.println("
");
out.println("");
out.println("Special thanks to ChatServlet for acting as our back-end");
out.println("");
out.println("");
}
// Accepts messages for broadcast.
public void doPost(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
// If our first request happens to be a POST, we need to set "chat"
// and start our update thread just like we do for a GET request.
if (chat == null) {
chat = (ChatServlet)ServletUtils.getServlet(
"ChatServlet", req, getServletContext());
if (chat != null) {
update = new Thread(this);
update.start();
Thread.currentThread().yield(); // let the run() method start
}
}
// Get the client's username. It's non-null only if ChatPage is
// protected by client authentication.
String user = req.getRemoteUser();
if (user == null) user = "anonymous";
// Get and broadcast the message.
String message = req.getParameter("message");
if (message != null && chat != null) {
chat.broadcastMessage(user + ": " + message);
Thread.currentThread().yield(); // let the message be broadcast
}
// Have doGet() print the updated message archive and the form.
doGet(req, res);
}
// Stops the background thread.
public void destroy() {
if (update != null)
update.stop();
}
public String getServletInfo() {
return "An HTML chat server front end, reusing ChatServlet";
}
}