Use of synchronized queue for java socket communications

Question

Hi all,
We have a need for a server socket application (stand alone java application) to process just one command per time coming from a java socket client (JSP Web application). There are a lot of users accessing the java socket client, but the server socket can only handle one command per time, so there is a need of a queue type, so users will have to wait for their time.
We've been told that we can use "synchronized Queue", but we don't know what it is and how to use. A URL, book etc. with sample code would assist us, since we are new to both java socket communication and queue of commands.
Can anyone assist us
cheers
Trajano
P.S.
The server socket java application has two threads:
1st thread handles the java socket communication;
2nd thread is a RS-232 serial driver that communicates to several micro-controllers connected on a multi-drop.
JSP web app client socket users can issue various commands at the same time to the java server socket app, however the server can only service one command per time (just one RS-232 COM1 serial port available). The commands have to somehow be added to a queue for processing.

Answer 1

I do not have the experience to offer advice. But I just happened to be reading today about Collections.synchronizedList.
import java.util.List;
import java.util.LinkedList;
import java.util.Collections;
public class Queue {
   private List queue;
   public Queue() {
      queue = Collections.synchronizedList(new LinkedList());
   public Object removeItem() throws InterruptedException {
      synchronized (queue) {
         while (queue.isEmpty())
            queue.wait();
         return queue.remove(0);
   public void addItem(Object item) {
      synchronized (queue) {
         queue.add(item);
         queue.notifyAll();
class Test {
   public static void main(String[] args) {
      final Queue queue = new Queue();
      //start a thread to process items from the queue
      Runnable work = new Runnable() {
         public void run() {
            try {
               Object item = queue.removeItem();
               //do something with item
            } catch (InterruptedException e) {
               //handle this
      Thread worker = new Thread(work);
      worker.start();
}Reference: Java Thread Programming, Paule Hyde
Also, here is Doug Lea's library,
http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html