Need help with simple file sharing application

Question

I have an assignment to build a Java File Sharing application. Since I'm relatively new to programming, this is not gonna be an easy task for me.
Therefore I was wondering if there are people willing to help me in the next few days. I will ask questions in this thread, there will be loads of them.
I already have something done but I'm not nearly halfway finished.
Is there a code example of a simple file sharing application somewhere? I didn't manage to find it.
More-less, this is what it needs to contain:
-client/server communication (almost over)
-file sending (upload, download)
-file search function (almost over)
-GUI of an application.
GUI is something I will do at the end, hopefully.
I hope someone will help me. Cheers
One more thing, I'm not asking for anyone to do my homework. I will only be needing some help in the various steps of building an application.
As I said code examples are most welcome.
This is what I have done so far
Server:
package ToJeTo;
import java.io.*;
import java.net.*;
public class MultiServer {
    public static ServerSocket serverskiSoket;
    public static int PORT = 1233;
    public static void main(String[] args) throws IOException {
        try {
            serverskiSoket = new ServerSocket(PORT);
        }catch (IOException e) {
            System.out.println("Connection impossible");
            System.exit(1);
        do {
            Socket client = serverskiSoket.accept();
            System.out.println("accepted");
            ClientHandler handler = new ClientHandler(client);
            handler.start();
        } while(true);
}Client:
package ToJeTo;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.*;
import java.util.Scanner;
public class MultiClient {
    public static InetAddress host;
    public static int PORT = 1233;
    public static void main(String[] args) {
        try {
            host = InetAddress.getLocalHost();
        }catch (UnknownHostException uhe) {
            System.out.println("Error!");
            System.exit(1);
        sendMessages();
    private static void sendMessages() {
        Socket soket = null;
        try {
            soket = new Socket(host, PORT);
            Scanner networkInput = new Scanner(soket.getInputStream());
            PrintWriter networkOutput = new PrintWriter(soket.getOutputStream(), true);
            Scanner unos = new Scanner(System.in);
            String message, response;
            do {
                System.out.println("Enter message");
                message = unos.nextLine();
                networkOutput.println(message);
                response = networkInput.nextLine();
                System.out.println("Server: " + response);
            }while (!message.equals("QUIT"));
        } catch (IOException e) {
            e.printStackTrace();
        finally {
            try{
                System.out.println("Closing..");
                soket.close();
            } catch (IOException e) {
                System.out.println("Impossible to disconnect!");
                System.exit(1);
}ClientHandler:
package ToJeTo;
import java.io.*;
import java.net.*;
import java.util.*;
public class ClientHandler extends Thread {
    private Socket client;
    private Scanner input;
    private PrintWriter output;
    public ClientHandler(Socket serverskiSoket) {
        client = serverskiSoket;
        try {
        input = new Scanner(client.getInputStream());
        output = new PrintWriter(client.getOutputStream(), true);
        } catch (IOException e) {
            e.printStackTrace();
        public void run() {
            String received;
            do {
            received = input.nextLine();
            output.println("Reply: " + received);
            } while (!received.equals("QUIT"));
            try {
                if (client != null)
                    System.out.println("Closing the connection...");
                    client.close();
            }catch (IOException e) {
                System.out.println("Error!");
}Those three classes are simple client server multi-threaded connection.

Answer 1

Now the other part that contains the search function looks like this:
package ToJeTo;
import java.io.*;
import java.util.*;
public class User {
    String nickname;
    String ipAddress;
    static ArrayList<String> listOfFiles = new ArrayList<String>();
    File sharedFolder;
    String fileLocation;
    public User(String nickname, String ipAddress, String fileLocation) {
        this.nickname = nickname.toLowerCase();
        this.ipAddress = ipAddress;
        sharedFolder = new File(fileLocation);
        File[] files = sharedFolder.listFiles();
        for (int i = 0; i < files.length; i++) {
            listOfFiles.add(i, files.toString().substring(fileLocation.length()+1));
public static void showTheList() {
for (int i = 0; i < listOfFiles.size(); i++) {
System.out.println(listOfFiles.get(i).toString());
@Override
public String toString() {
return nickname + " " + ipAddress;
User Manager:
package ToJeTo;
import java.io.*;
import java.util.*;
class UserManager {
    static ArrayList<User> allTheUsers = new ArrayList<User>();;
    public static void addUser(User newUser) {
        allTheUsers.add(newUser);
    public static void showAndStoreTheListOfUsers() throws FileNotFoundException, IOException {
        BufferedWriter out = new BufferedWriter(new FileWriter("List Of Users.txt"));
        for (int i = 0; i < allTheUsers.size(); i++) {
                System.out.println(allTheUsers.get(i));
                out.write(allTheUsers.get(i).toString());
                out.newLine();
        out.close();
}Request For File
package ToJeTo;
import java.util.*;
public class RequestForFile {
    static ArrayList<String> listOfUsersWithFile = new ArrayList<String>();
    Scanner input;
    String fileName;
    public RequestForFile() {
        System.out.println("Type the wanted filename here: ");
        input = new Scanner(System.in);
        fileName = input.nextLine();
        for (User u : UserManager.allTheUsers) {
            for (String str : User.listOfFiles) {
                if (str.equalsIgnoreCase(fileName))
                    listOfUsersWithFile.add(u.nickname);
    public RequestForFile(String fileName) {
        for (User u : UserManager.allTheUsers) {
            for (String str : User.listOfFiles) {
                if (str.equalsIgnoreCase(fileName))
                    listOfUsersWithFile.add(u.nickname);
    public static List<String> getAll() {
        for (int i = 0; i < listOfUsersWithFile.size(); i++) {
            //System.out.println("User that has the file: " + listOfUsersWithFile.get(i));
        return listOfUsersWithFile;
}Now this is the general idea.
The user logs in with his nickname and ip address. He defines his own shared folder and makes it available for other users that log on to server.
Now each user has their own list of files from a shared folder. It's an ArrayList.
User manager class is there to store another list, a list of users that are connected with server.
When the user is searching for a particular file, he is searching through all the users and their respective files lists. Therefore for each loop inside a for each loop.
Now the problem is how to connect all that with Client and Server class and put it into one piece.
GUI should look somewhat like this: