java - 请使用Java中的多线程

Question

我是一个新的java程序员，我有一个文件共享程序，我试图让它在多线程的while(true)循环中连续工作。我的服务器运行正常，但我可以使客户端连续运行，例如服务器建立连接，然后我运行客户端，但我必须手动运行它，因为文件传输后，客户端停止。下面是代码，你能帮我纠正错误吗？

import java.net.*;
import java.io.*;
public class TCPServer
{
private static ServerSocket myServer;
private static Socket myClient = null;

public static void main(String[] args) throws IOException
{

    try
    {
        myServer = new ServerSocket(6789);
        System.out.println("Server is now available...");
    }
    catch(Exception e)
    {
        System.err.println("This port is unavailable.");
        System.exit(1);
    }

    while(true)
    {
        try
        {
            myClient = myServer.accept();
            System.out.println("Connection established to : " + myClient);
            Thread t = new Thread(new ConnectionThread(myClient));
            t.start();
        }catch(Exception e)
        {
            System.err.println("Connection failed...!");
        }
    }
}
}

import java.net.*;
import java.io.*;
public class TCPClient
{
private static BufferedReader myReader;
private static PrintStream myOut;
private static String fileName;
private static Socket mySocket;

public static void main(String[] args) throws IOException
{
    try
    {
        mySocket = new Socket("localhost", 6789);
        myReader = new BufferedReader(new InputStreamReader(System.in));
    }
    catch(Exception e)
    {
        System.err.println("Couldn't establish a connection with server.");
        System.exit(1);
    }
    try
    {

        myOut = new PrintStream(mySocket.getOutputStream());
        switch (Integer.parseInt(sendOrReceive()))
        {
            case 1:
                    myOut.println("1");
                    sendFile();
                    break;
            case 2:
                    myOut.println("2");
                    System.err.print("Enter file name: ");
                    fileName = myReader.readLine();
                    myOut.println(fileName);
                    receiveFile(fileName);
                    break;
        }
        mySocket.close();
    }
    catch(Exception e)
    {
        System.err.println("not valid input");
    }
}

public static String sendOrReceive() throws IOException
{
    System.out.println("1. Send file.");
    System.out.println("2. Recieve file.");
    System.out.print("\nMake selection: ");

    return myReader.readLine();
}

public static void sendFile()
{
    try
    {
        System.err.print("Enter file name: ");
        fileName = myReader.readLine();
        File myFile = new File("F:/" + fileName);
        byte[] myArray = new byte[(int) myFile.length()];

        FileInputStream myInFileStream = new FileInputStream(myFile);
        BufferedInputStream myBufferStream = new BufferedInputStream(myInFileStream);

        DataInputStream myDataIn = new DataInputStream(myBufferStream);
        myDataIn.readFully(myArray, 0, myArray.length);

        OutputStream myOutStream = mySocket.getOutputStream();

        //Sending file name and file size to the server
        DataOutputStream myDataOut = new DataOutputStream(myOutStream);
        myDataOut.writeUTF(myFile.getName());
        myDataOut.writeLong(myArray.length);
        myDataOut.write(myArray, 0, myArray.length);
        myDataOut.flush();
        System.out.println("The file " + fileName + " was sent to the server.");
    }
    catch (Exception e)
    {
        System.err.println("The file " + fileName + " was not found!");
    }
}

public static void receiveFile(String fileName)
{
    try
    {
        InputStream myIn = mySocket.getInputStream();
        DataInputStream myDataOut = new DataInputStream(myIn);
        fileName = myDataOut.readUTF();
        OutputStream myOut = new FileOutputStream(("F:/" + fileName));
        long file =  myDataOut.readLong();
        byte[] buffer = new byte[1024];
        int num = 0;
        while (file  > 0 && num != -1)
        {
            num =  myDataOut.read(buffer, 0, (int) Math.min(buffer.length, file));
            myOut.write(buffer, 0, num);
            file  -= num;
        }
        myOut.close();
        myIn.close();
        myDataOut.close();
        System.out.println("The file " + fileName + " was received from the server.");
    }
    catch(IOException ex)
    {
        System.err.println("Connection closed.");
    }
}
}

public class ConnectionThread implements Runnable
{
private Socket clientSocket;
private BufferedReader myBuffer = null;

public ConnectionThread(Socket aSocket)
{
    this.clientSocket = aSocket;
}

@Override
public void run()
{
    try
    {

        myBuffer = new BufferedReader(new InputStreamReader(
                clientSocket.getInputStream()));
        String choice = "";
        while((choice = myBuffer.readLine()) != null)
        {
            switch (choice)
            {
                case "1":
                            receiveFile();
                            break;
                case "2":
                            String fileName;
                            while ((fileName = myBuffer.readLine()) != null)
                            {
                                sendFile(fileName);
                            }
                            break;
                 default:
                            System.out.println("Not a valid choice. Choice must be '1' or '2'.");
                            break;
            }
            myBuffer.close();
            clientSocket.close();
            break;
        }
    }
    catch(IOException e)
    {
         e.printStackTrace();
    }
}

public void receiveFile()
{
    try
    {
        DataInputStream myDataOut = new DataInputStream(clientSocket.getInputStream());
        String fileName = myDataOut.readUTF();
        FileOutputStream myOut = new FileOutputStream(("C:/SHARED/" + fileName));
        long file = myDataOut.readLong();
        byte[] buffer = new byte[1024];
        int num = 0;
        while (file  > 0 && num != -1)
        {
            num = myDataOut.read(buffer, 0, (int) Math.min(buffer.length, file));
            myOut.write(buffer, 0, num);
            file -= num;
        }
        myOut.close();
        myDataOut.close();
        System.out.println("The file " + fileName + " was received from the client.");
    }catch (IOException e)
    {
        System.err.println("Connection closed.");
    }
}

public void sendFile(String fileName)
{
    try
    {
        //handle file read
        File myFile = new File("C:/Users/" + fileName);
        byte[] myArray = new byte[(int) myFile.length()];

        FileInputStream myInFileStream = new FileInputStream(myFile);
        BufferedInputStream myInBufferStream = new BufferedInputStream(myInFileStream);

        DataInputStream myDataIn = new DataInputStream(myInBufferStream);
        myDataIn.readFully(myArray, 0, myArray.length);

        //handle file send over socket
        OutputStream myOutStream = clientSocket.getOutputStream();

        //Sending file name and file size to the server
        DataOutputStream myDataOut = new DataOutputStream(myOutStream);
        myDataOut.writeUTF(myFile.getName());
        myDataOut.writeLong(myArray.length);
        myDataOut.write(myArray, 0, myArray.length);
        myDataOut.flush();
        System.out.println("The file " + fileName + " was sent to the client.");
    }
    catch(Exception e)
    {
        System.err.println("The file " + fileName + " was not found!");
    } 
}
}

Answer 1

我认为你可以在客户端的 main 中添加一个循环，正如 Saket 在评论中所说:

public static void main(String[] args) throws IOException
{
    while(true) {
        try
        {
            mySocket = new Socket("localhost", 6789);
            myReader = new BufferedReader(new InputStreamReader(System.in));
        }
        ...
        ...
    }
}

您可以添加选项“3”来结束循环和客户端程序:

case 3:
    System.exit(0);

如果您想使用单个客户端一次下载多个文件，则需要线程。