Java 对等网络应用程序 - 作业

Java Peer-to-Peer networking application - homework

提问by user1998719

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 PeerNodeis 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?

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

Following code represents one peer node:

以下代码代表一个对等节点：

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();
        }

    }
}

And following class creates all the nodes and connects them:

以下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";
    }
 }

回答by uldall

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

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，您的循环createNodes仅创建第一个 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();