Java 对等网络应用程序 - 作业

Question

我正在用 Java 创建一个用于文件共享的 p2p 应用程序。每个对等节点都将在我的机器上的不同端口上运行并监听请求。但我遇到的问题是，当创建 PeerNode 实例时，我的代码会进入无限循环。以下是我的 PeerNode 代码。这是我应该如何创建每个节点并让它们监听传入请求吗？

以下代码表示一个对等节点:

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();
        }

    }
}

下面的类创建所有节点并连接它们:

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

您的 PeerNode 构造函数永远不会返回，因为它正忙于接受新连接。因此，您在 createNodes 中的循环只会创建第一个 PeerNode 实例。您可以通过在新线程中调用 startClientServer 来解决此问题:

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