number-listener/Server.java

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.net.ServerSocket;
import java.util.*;

/*
    Server to create socket and manage threads of client connections.
 */
public class Server {

    private final boolean DEBUG = false;
    private final int NUMSOCKETS = 5;       //Number of socket threads to run
    private final int REFRATE = 10;          //Refresh period of report, in seconds
    private final String fileName = "numbers.log";

    private ServerSocket serverSocket;
    private SocketThread[] threads;
    private ThreadGroup threadGroup;
    private int port;
    private boolean active;
    private long refTime;
    private ArrayList<String> uniqueList;  //A final list of all the unique 9 digit numbers
    private List<String> incomingList;//A list to hold all new numbers from socket threads
    private int totalUniqueCount;
    private int newUniqueCount;
    private int newDupesCount;
    private BufferedWriter writer;

    //initialize variables, open the socket.
    public Server(int port) {
        try {
            writer = new BufferedWriter(new FileWriter(fileName));
        } catch (IOException e) {
            e.printStackTrace();
        }
        totalUniqueCount = 0;
        newUniqueCount = 0;
        newDupesCount = 0;
        refTime = System.nanoTime();

        this.port = port;
        active = true;
        threads = new SocketThread[5];
        threadGroup = new ThreadGroup("socket threads");
        uniqueList = new ArrayList<String>();
        incomingList = Collections.synchronizedList(new LinkedList<String>());  //thread safe list
    }

    //Start the server, called by main
    public void start() {
        try {
            serverSocket = new ServerSocket(port);
        } catch (IOException e) {
            e.printStackTrace();
        }

        //start all socket threads
        for (int i = 0; i < NUMSOCKETS; i++) {
            threads[i] = new SocketThread(threadGroup, serverSocket, incomingList);
            threads[i].start();
        }

        //Loop forever while all 5 threads running.
        while (threadGroup.activeCount() == NUMSOCKETS) {

            //Update unique list and print report every refresh period
            if ((System.nanoTime() - refTime) / 1000000000 > REFRATE) {

                updateList();
                displayReport();
                refTime = System.nanoTime();
            }

        }

        stop();                     // a thread stops running, implies terminate. Stop the server
        updateList();               //Last update after stopping all connections.
        try {
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    //Method called to stop all threads and shut down the server
    public void stop() {

        //First, Loop through all threads and tell them to release clients and self-terminate
        for (int i = 0; i < NUMSOCKETS; i++) {
            if ((threads[i] != null) && (threads[i].isAlive())) {
                threads[i].setTerminate(true);
                threads[i].setRelease(true);
            }
        }

        //Second, Wait for each thread to die
        for (int i = 0; i < NUMSOCKETS; i++) {

            try {
                //Close the server socket
                serverSocket.close();

                //If the thread is still running now, wait for it to die
                if (threads[i] != null && threads[i].isAlive()) {
                    threads[i].join();
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        threadGroup.destroy();           //If all threads dead, group will destroy without error
        active = false;
    }


    //Update list of unique new numbers from the list of incoming numbers
    private void updateList() {
        int index = uniqueList.size();
        int newSize = 0;
        newUniqueCount = 0;
        newDupesCount = 0;

        //Cannot allow other threads to modify incomingList while we are working with it.
        synchronized (incomingList) {
            uniqueList.addAll(incomingList);
            incomingList.clear();
        }

        //Calculating report data
        newDupesCount = removeDupes(uniqueList);
        newSize = uniqueList.size();
        newUniqueCount = newSize - index;
        totalUniqueCount = newSize;

        for (int i = index; i < uniqueList.size(); ++i) {
            updateFile(uniqueList.get(i));
        }
    }

    //Print report to console
    private void displayReport() {
        // System.out.print("\033[H\033[2J");              //clear the console (optional)
        System.out.println("Received " + newUniqueCount + " unique numbers, "
                + newDupesCount + " duplicates. Unique total: " + totalUniqueCount);
    }

    //Write the parameter string to the log file
    private void updateFile(String newNum) {
        try {
            writer.write(newNum);
            writer.newLine();
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //Allow main program to check if server is still active.
    public boolean getActive() {
        return this.active;
    }

    //Remove duplicate entries from src list and return number of duplicates
    private int removeDupes(ArrayList<String> src) {
        if (src == null || src.size() < 2) {
            return 0;
        }
        int size = src.size();
        LinkedHashSet<String> noDupes = new LinkedHashSet<String>(src);
        src.clear();
        src.addAll(noDupes);
        return size - src.size();
    }

}