public class Server_app {

    private final int port = 12345;
    private ServerSocket serverSocket;
    private Socket socket;
    private InputStream in;
    private OutputStream out;
    private FileInputStream fileReader;
    private DataInputStream inData;
    private DataOutputStream outData;
    private String[] fileList;
    private final Map<String, Integer> downloadStats = new TreeMap<>();
    private final File serverFolder = new File("C:\\testdir");
    private File[] serverFiles;
    private String command;
    private String fileContent;
    private List<String> log = new ArrayList<>();
    private int n;
    private FileWriter logWriter;
    private FileWriter statsWriter;

    public static void main(String[] args) {
        Server_app s = new Server_app();
        s.runServer();
        s.fillFileList();
        s.setDownloadCounters();
        s.recieveCommands();
    }

    public void runServer() {
        try {
            serverSocket = new ServerSocket(port);
            message("Server started");
            message("to stop the server you can use -exit command \n");
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }

    public void fillFileList() {
        if (serverFolder.exists() && serverFolder.isDirectory() && serverFolder.canRead()) {
            fileList = serverFolder.list();
        }
    }

    public void setDownloadCounters() {
        for (String fileName : fileList) {
            downloadStats.put(fileName, 0);
        }
    }

    public void increaseDownloadCounters(String fileName) {
        for (Map.Entry<String, Integer> entry : downloadStats.entrySet()) {
            if (entry.getKey().equals(fileName)) {
                int tmp = entry.getValue();
                entry.setValue(++tmp);
            }
        }
    }

    public void recieveCommands() {
        try {
            while (true) {
                socket = serverSocket.accept();
                in = socket.getInputStream();
                out = socket.getOutputStream();
                inData = new DataInputStream(in);
                outData = new DataOutputStream(out);
                message("Got a connection from " + socket.getInetAddress() + ":" + socket.getPort());
                command = inData.readUTF();
                if (command.equals("-getFilesList")) {
                    message("Recieved command: " + command + " from: " + socket.getInetAddress() + ":" + socket.getPort());
                    sendFileList();
                    message("FileList was sended to " + socket.getInetAddress() + ":" + socket.getPort());
                }
                if (command.contains("-download ")) {
                    boolean b = false;
                    for (String fileName : fileList) {                       
                        if (command.contains(fileName)) {
                            b = true;
                            message("Recieved command: " + command + " from: " + socket.getInetAddress() + ":" + socket.getPort());
                            sendFile();
                            message("File was sended to " + socket.getInetAddress() + ":" + socket.getPort());
                        }
                    }
                    if (b==false){
                      outData.writeUTF("File not found on server, check filelist");
                      outData.writeUTF("File not found on server, check filelist");
                      message("File not found on server, check filelist");
                    }
                }
                if (!command.equals("-getFilesList") && !command.contains("-download ")) {
                    outData.writeUTF("Unknown command \"" + command + "\"");
                    outData.writeUTF("Unknown command \"" + command + "\"");
                    message("Unknown command \"" + command + "\"" + " from " + socket.getInetAddress() + ":" + socket.getPort());
                }
            }
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }

    public void sendFileList() throws IOException {
        StringBuilder sb = new StringBuilder();
        sb.append("FileList:").append("\n");
        for (String fileName : fileList) {
            sb.append(fileName).append("\n");
        }
        outData.writeUTF(sb.toString());
    }

    public void sendFile() throws IOException {
        writeLogFile();
        serverFiles = serverFolder.listFiles();
        for (File serverFile : serverFiles) {
            if (command.contains(serverFile.getName())) {
                outData.writeUTF(command);
                fileReader = new FileInputStream(new File(serverFile.getAbsolutePath()));
                byte[] buffer = new byte[fileReader.available()];
                while (fileReader.available() > 0) {
                    n = fileReader.read(buffer);
                }
                fileContent = new String(buffer, 0, n);
                outData.writeUTF(fileContent);
                increaseDownloadCounters(serverFile.getName());
                writeStatistics();
            } 
        }
    }

    public void writeLogFile() {
        try {
            int x = 0;
            logWriter = new FileWriter(serverFolder + "\\server_log.txt", true);
            for (String logMessage : log) {
                logWriter.write(logMessage);
                logWriter.write(System.getProperty("line.separator"));
                ++x;
                if (x == 2) {
                    logWriter.write(System.getProperty("line.separator"));
                }
            }
            logWriter.close();
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }

    public void writeStatistics() {
        try {
            statsWriter = new FileWriter(serverFolder + "\\download_stats.txt");
            for (Map.Entry<String, Integer> entry : downloadStats.entrySet()) {
                statsWriter.write(entry.getKey() + " downloads: " + entry.getValue());
                statsWriter.write(System.getProperty("line.separator"));
            }
            statsWriter.close();
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }

    public void serverShutdown() {
        BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
        while (true) {
            try {
                String s = r.readLine();
                if (s.equals("-exit")) {
                    in.close();
                    out.close();
                    inData.close();
                    outData.close();
                    socket.close();
                    serverSocket.close();
                    message("Server shutdown");
                }
            } catch (IOException ex) {
                message(ex.getMessage());
            }
        }
    }

    public void message(String msg) {
        System.out.println(msg);
        log.add(msg);
    }
}

public class Client_App {

    private String strAddress = "127.0.0.1";
    private int port = 12345;
    private InputStream in;
    private OutputStream out;
    private DataInputStream inData;
    private DataOutputStream outData;
    private DataOutputStream fileData;
    private InetAddress ipAddress;
    private Socket socket;
    private String response;
    private String fileContent;
    private FileOutputStream fileWriter;
    private final File outputDir = new File("C:\\downloads");
    private String[] recievedFileName;
    private List<String> log = new ArrayList<>();
    private FileWriter logWriter;

    public static void main(String[] args) {
        Client_App client_App = new Client_App();
        client_App.runClient();
        client_App.sendCommands();
    }

    public void runClient() {
        try {
            ipAddress = InetAddress.getByName(strAddress);
            socket = new Socket(ipAddress, port);
            in = socket.getInputStream();
            out = socket.getOutputStream();
            inData = new DataInputStream(in);
            outData = new DataOutputStream(out);
            message("Client started");
            message("You can enter the following commands: ");
            message("-getFilesList");
            message("-download %file_name.file_extension%");
            message("-exit \n ");
        } catch (UnknownHostException ex) {
            message(ex.getMessage());
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }

    public void sendCommands() {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        while (true) {
            try {
                String s = reader.readLine();
                if (s.equals("-exit")) {
                    in.close();
                    out.close();
                    inData.close();
                    outData.close();
                    socket.close();
                    message("Client shutdown");
                    break;
                }
                if (s.equals("-getFilesList")) {
                    outData.writeUTF(s);
                    response = inData.readUTF();
                    recieveResponse(response);
                } else {
                    outData.writeUTF(s);
                    response = inData.readUTF();
                    fileContent = inData.readUTF();
                    if (response.equals(fileContent)) {
                        message(response);
                    } else {
                        recieveResponse(response, fileContent);
                    }
                }
            } catch (IOException ex) {
                message(ex.getMessage());
            }
        }
    }

    public void recieveResponse(String fileName) {
        if (response.contains("FileList:")) {
            recieveFileList();
        } else {
            message(response);
        }
    }

    public void recieveResponse(String fileName, String fileContent) {
        recievedFileName = response.split("-download ");
        recieveFile(recievedFileName[1]);
    }

    public void recieveFileList() {
        message(response);
    }

    public void recieveFile(String recievedfileName) {
        if (outputDir.exists() && outputDir.isDirectory() && outputDir.canWrite()) {
            writeDownloadedFile(recievedfileName);
            message(recievedfileName + " was downloaded in existing directory");
            writeLogFile();
        } else if (!outputDir.exists()) {
            outputDir.mkdir();
            writeDownloadedFile(recievedfileName);
            message(recievedfileName + " was downloaded in new directory");
        }
    }

    public void writeDownloadedFile(String recievedfileName) {
        try {
            fileWriter = new FileOutputStream(new File(outputDir + "\\" + recievedfileName));
            fileData = new DataOutputStream(fileWriter);
            fileData.writeUTF(fileContent);
            fileWriter.close();
            fileData.close();
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }

    public void message(String msg) {
        System.out.println(msg);
        log.add(msg);
    }

    public void writeLogFile() {
        try {
            int x = 0;
            logWriter = new FileWriter(outputDir + "\\client_log.txt");
            for (String logMessage : log) {
                logWriter.write(logMessage);
                logWriter.write(System.getProperty("line.separator"));
                ++x;
                if (x == 5) {
                    logWriter.write(System.getProperty("line.separator"));
                }
            }
            logWriter.close();
        } catch (IOException ex) {
            message(ex.getMessage());
        }
    }
}

fileReader = new FileInputStream(new File(serverFile.getAbsolutePath()));
                byte[] buffer = new byte[fileReader.available()];
                while (fileReader.available() > 0) {
                    fileReader.read(buffer);                   
                }

outData.write(buffer);

      buffer = new byte[inData.available()];
                    inData.readFully(buffer);