I have implemented the two classes shown at http://tomcat.apache.org/tomcat-6.0-doc/aio.html which gives a messenger application using Tomcat’s comet implementation.
How do I connect this to a web interface and get something to display.
I am thinking these are the basic steps (I don’t know the details).
- I should create some traditional event – a button click or AJAX event – that calls the ChatServlet and passes in a CometEvent (somehow) – perhaps BEGIN
- From then I have my code call the event method every time I want to send something to the client using the READ event as the input parameter.
I have copied the two classes below:
package controller;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.catalina.CometEvent;
import org.apache.catalina.CometProcessor;
public class ChatServlet extends HttpServlet implements CometProcessor {
protected ArrayList<HttpServletResponse> connections = new ArrayList<HttpServletResponse>();
protected MessageSender messageSender = null;
public void init() throws ServletException {
messageSender = new MessageSender();
Thread messageSenderThread = new Thread(messageSender, "MessageSender["
+ getServletContext().getContextPath() + "]");
messageSenderThread.setDaemon(true);
messageSenderThread.start();
}
public void destroy() {
connections.clear();
messageSender.stop();
messageSender = null;
}
/**
* Process the given Comet event.
*
* @param event
* The Comet event that will be processed
* @throws IOException
* @throws ServletException
*/
public void event(CometEvent event) throws IOException, ServletException {
HttpServletRequest request = event.getHttpServletRequest();
HttpServletResponse response = event.getHttpServletResponse();
if (event.getEventType() == CometEvent.EventType.BEGIN) {
log("Begin for session: " + request.getSession(true).getId());
PrintWriter writer = response.getWriter();
writer
.println("<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">");
writer
.println("<head><title>JSP Chat</title></head><body bgcolor=\"#FFFFFF\">");
writer.flush();
synchronized (connections) {
connections.add(response);
}
} else if (event.getEventType() == CometEvent.EventType.ERROR) {
log("Error for session: " + request.getSession(true).getId());
synchronized (connections) {
connections.remove(response);
}
event.close();
} else if (event.getEventType() == CometEvent.EventType.END) {
log("End for session: " + request.getSession(true).getId());
synchronized (connections) {
connections.remove(response);
}
PrintWriter writer = response.getWriter();
writer.println("</body></html>");
event.close();
} else if (event.getEventType() == CometEvent.EventType.READ) {
InputStream is = request.getInputStream();
byte[] buf = new byte[512];
do {
int n = is.read(buf); // can throw an IOException
if (n > 0) {
log("Read " + n + " bytes: " + new String(buf, 0, n)
+ " for session: "
+ request.getSession(true).getId());
} else if (n < 0) {
// error(event, request, response);
System.out.println("you have an error");
return;
}
} while (is.available() > 0);
}
}
}
package controller;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import javax.servlet.http.HttpServletResponse;
public class MessageSender implements Runnable {
protected boolean running = true;
protected ArrayList<String> messages = new ArrayList<String>();
protected ArrayList<HttpServletResponse> connections = new ArrayList<HttpServletResponse>();
public MessageSender() {
}
public void stop() {
running = false;
}
/**
* Add message for sending.
*/
public void send(String user, String message) {
synchronized (messages) {
messages.add("[" + user + "]: " + message);
messages.notify();
}
}
public void run() {
while (running) {
if (messages.size() == 0) {
try {
synchronized (messages) {
messages.wait();
}
} catch (InterruptedException e) {
// Ignore
}
}
synchronized (connections) {
String[] pendingMessages = null;
synchronized (messages) {
pendingMessages = messages.toArray(new String[0]);
messages.clear();
}
// Send any pending message on all the open connections
for (int i = 0; i < connections.size(); i++) {
try {
PrintWriter writer = connections.get(i).getWriter();
for (int j = 0; j < pendingMessages.length; j++) {
writer.println(pendingMessages[j] + "<br>");
}
writer.flush();
} catch (IOException e) {
System.out.println("IOExeption sending message" + e);
}
}
}
}
}
}
Here you have a complete example for Tomcat with source code to download at the bottom:Developing with Comet and Java