Java Peer-to-Peer networking application - homework

Question

I'm creating a p2p application in Java for file sharing. Each peer node will be running on my machine on a different port and listen for a request. but the problem I'm running into is when an instance of PeerNode is created my code runs into an infinite loop. Following is my code for PeerNode. Is this how I should create each node and have them listen for incoming requests?

Following code represents one peer node:

public class PeerNode
{
    private int port;
    private ArrayList<PeerNode> contacts;
    PeerNode preNode;
    PeerNode postNode;
    private String directoryLocation = "";

    PeerNode(int port)
    {
        this.port = port;
        this.setDirectoryLocation( port+"");
        startClientServer( port );
    }

    private void sendRequest(String fileName, String host, int port) throws UnknownHostException, IOException
    {
        Socket socket = new Socket(host, port);//machine name, port number
        PrintWriter out = new PrintWriter( socket.getOutputStream(), true );
        out.println(fileName);

        out.close();
        socket.close();

    }

    private void startClientServer( int portNum )
    {
        try 
        {
            // Establish the listen socket.
            ServerSocket server = new ServerSocket( 0 );
            System.out.println("listening on port " + server.getLocalPort());

            while( true )
            {
                // Listen for a TCP connection request.
                Socket connection = server.accept();

                // Construct an object to process the HTTP request message.
                HttpRequestHandler request = new HttpRequestHandler( connection );

                // Create a new thread to process the request.
                Thread thread = new Thread(request);

                // Start the thread.
                thread.start();

                System.out.println("Thread started for "+ portNum);
            }

        } 
        catch (Exception e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

And following class creates all the nodes and connects them:

public class MasterClientServer 
{
    public static void main( String [] args )
    {
        int count = 10;
        ArrayList<PeerNode> arrayOfNodes = createNodes( count );
    }

    public static ArrayList<PeerNode> createNodes( int count)
    {
        System.out.println("Creating a network of "+ count + " nodes...");
        ArrayList< PeerNode > arrayOfNodes = new ArrayList<PeerNode>();

        for( int i =1 ; i<=count; i++)
        {
            arrayOfNodes.add( new PeerNode( 0 ) ); //providing 0, will take any free node
        }
        return arrayOfNodes;
    }
}



public class HttpRequestHandler implements Runnable 
{
    final static String CRLF = "\r\n";
    Socket socket;

    public HttpRequestHandler(Socket socket) throws Exception 
    {
        this.socket = socket;
    }

    @Override
    public void run() 
    {
        try 
        {
            processRequest();
        } 
        catch (Exception e) 
        {
            System.out.println(e);
        }

    }   

    /*
     * Gets a request from another node. 
     * Sends the file to the node if available.
     */
    private void processRequest() throws Exception 
    {
        /*DataOutputStream os = new DataOutputStream(socket.getOutputStream());

        InputStream is = socket.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(is));

        // Get the request line of the HTTP request message.
        String requestLine = br.readLine();

        // Extract the filename from the request line.
        // In Get request, the second token is the fie name
        String[] tokens = requestLine.split(" ");
        String fileName = tokens[1];

        // Prepend a "." so that file request is within the current directory.
        fileName = "." + fileName;

        // Open the requested file.
        FileInputStream fis = null;
        boolean fileExists = true;

        try 
        {
            fis = new FileInputStream(fileName);
        } 
        catch (FileNotFoundException e) 
        {
            fileExists = false;
        }

        // construct the response Message
        // Construct the response message.
        String statusLine = null;
        String contentTypeLine = null;
        String entityBody = null;
        if (fileExists) 
        {
            statusLine = "HTTP/1.1 200 OK" + CRLF;
            contentTypeLine = "Content-Type: " + contentType(fileName) + CRLF;
        } 
        else 
        {
            statusLine = "HTTP/1.1 404 Not Found" + CRLF;
            contentTypeLine = "Content-Type: text/html" + CRLF;
            entityBody = "<HTML><HEAD><TITLE>404 Not Found</TITLE></HEAD><BODY>Error 404: Page Not Found</BODY></HTML>";
        }

        // Send the status line.
        os.writeBytes(statusLine);

        // Send the content type line.
        os.writeBytes(contentTypeLine);

        // Send a blank line to indicate the end of the header lines.
        os.writeBytes(CRLF);

        // Send the entity body.
        if (fileExists) {
            sendBytes(fis, os);
            fis.close();
        } else {
            os.writeBytes(entityBody);
        }
        // Close streams and socket.
        os.close();
        br.close();
        socket.close();

    }

    private static void sendBytes(FileInputStream fis, OutputStream os)
            throws Exception 
            {
        // Construct a 1K buffer to hold bytes on their way to the socket.
        byte[] buffer = new byte[1024];
        int bytes = 0;

        // Copy requested file into the socket's output stream.
        while ((bytes = fis.read(buffer)) != -1) {
            os.write(buffer, 0, bytes);
        }*/
    }

    private static String contentType(String fileName) 
    {
        if (fileName.endsWith(".htm") || fileName.endsWith(".html")) 
        {
            return "text/html";
        }
        if (fileName.endsWith(".jpg") || fileName.endsWith(".jpeg")) 
        {
            return "image/jpeg";
        }
        if (fileName.endsWith(".gif")) {
            return "image/gif";
        }
        if (fileName.endsWith(".ram") || fileName.endsWith(".ra")) 
        {
            return "audio/x-pn-realaudio";
        }
        return "application/octet-stream";
    }
 }

Answer 1

Your PeerNode constructor never returns since it is busy accepting new connections. Hence your loop in createNodes only creates the first PeerNode instance. You can solve this by calling startClientServer in a new thread:

new Thread(new Runnable() {
   public void run() {
       startClientServer( port );
   }
}.start();